I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

wrote in message
ups.com

I just bought a clean Macintosh MA 6100 integrated amp at
a bricks and motar auction. I haven't done anything with
the 6100 other than plugging it in (all the lights work
and it didn't blow a breaker) and it will be a few days
before I can put it in my system and make an evaluation.

Seems like it could have signficant cash value if these MA 5100 prices are
any indication:

http://www.audioclassics.com/detail....MA5100&nav=cat


I currently have a Hafler 220 amp and Hafler 110 preamp.
I know that the Mac was built to the highest standards of
the mid 70s, but even my Hafler, a modest piece of
equipment, has poly caps, metal resistors, better pots
etc. If I like the way the Mac sounds, would it be
worthwhile or even desirable to upgrade individual
components? My system is two channel, music only and I
listen to FM, CDs and records.

Is sound quality *really* the most important thing to you?

I can't see how the MA 6100 would be much of an upgrade, other than neat
looks and bragging rights.

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

Don't assume that the Mac can be made to sound better. The Hafler has newer
semiconductors. Rapid progress was made in those years.

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

Don't assume that the Mac can be made to sound better. The Hafler has
newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright speakers.

The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would be a
much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They cannot
be recommended for any use.

"Robert Morein" said:


Don't assume that the Mac can be made to sound better. The Hafler has newer
semiconductors. Rapid progress was made in those years.


About the MOSFETs:
It was said that 2SK135/2SJ50 paired combos could be replaced with
BUZ900/BUZ905.
Physically, that's entirely true.
Soundwise, however, it's not.

Where IMO the 135/50 sounds best at 700....1000 mA idling current, I
have not been able to find such a sweet spot with the BUZ
replacements.

I only dared to push them up to 2.5A, still no match.
I feared launching them into orbit, so I stopped there.

Maybe our resident solid state experts know something about the
unknown territory beyond the 2.5A per device barrier, but I won't hold
my breath ;-)


Hitachis still rule, note.

--

- Never argue with idiots, they drag you down their level and beat you with experience. -

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

Don't assume that the Mac can be made to sound better. The Hafler has
newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all MOSFET
amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin
time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would be a
much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They
cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up in
smoke. Late model PLs did not suffer this problem. In any case, there are
better choices, but I was trying to make a point about how bad both amps
mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not to your
taste, but "bad" ?

"Sander deWaal" wrote in message
...
"Robert Morein" said:


Don't assume that the Mac can be made to sound better. The Hafler has
newer
semiconductors. Rapid progress was made in those years.


About the MOSFETs:
It was said that 2SK135/2SJ50 paired combos could be replaced with
BUZ900/BUZ905.
Physically, that's entirely true.
Soundwise, however, it's not.

Where IMO the 135/50 sounds best at 700....1000 mA idling current, I
have not been able to find such a sweet spot with the BUZ
replacements.

I only dared to push them up to 2.5A, still no match.
I feared launching them into orbit, so I stopped there.

Why? There's no thermal runaway. As long as they don't get too hot, they'll
be OK.

Maybe our resident solid state experts know something about the
unknown territory beyond the 2.5A per device barrier, but I won't hold
my breath ;-)


Hitachis still rule, note.

--

- Never argue with idiots, they drag you down their level and beat you
with experience. -

"Robert Morein" said:


I only dared to push them up to 2.5A, still no match.
I feared launching them into orbit, so I stopped there.


Why? There's no thermal runaway. As long as they don't get too hot, they'll
be OK.


I observed a slight increase in current with temperature, and my
heatsink was only 0.6 K/W ...... ;-)

Still didn't sound like the Hitachis, though.

Please remember that this experimental amp didn't have AC loop
feedback (just a DC servo loop).

--

- Never argue with idiots, they drag you down their level and beat you with experience. -

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

Don't assume that the Mac can be made to sound better. The Hafler has
newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented. The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin time.
They're both pretty ordinary amps. A late model Phase Linear would be a much
better (and cheaper) choice.


--
Trevor Wilson
www.rageaudio.com.au

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp.
I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would
it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The Hafler has
newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all MOSFET
amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin
time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would be a
much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They
cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up in
smoke. Late model PLs did not suffer this problem. In any case, there are
better choices, but I was trying to make a point about how bad both amps
mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not to your
taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time. Compression is
distortion. Distortion is bad.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" said:


**It compresses the sound, like all MOSFET amps of it's time. Compression is
distortion. Distortion is bad.


Just put enough of them in parallel, problem solved :-)
My record up until now is 8 * K135 vs. 8 * J50 in push pull per
channel....beefy driver needed!

BTW I kicked a box over at work today.....out came 4 PCBs with 4
Hitachis each. After asking my employer about them:
"Oh, yes, we used those in the old days. Please take 'em or toss 'em!"

I tossed them....in my parts bin.

--

- Never argue with idiots, they drag you down their level and beat you with experience. -

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

Don't assume that the Mac can be made to sound better. The Hafler has
newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all MOSFET
amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would be a
much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They
cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up in
smoke. Late model PLs did not suffer this problem. In any case, there are
better choices, but I was trying to make a point about how bad both amps
mentioned actually are.


--
Trevor Wilson
www.rageaudio.com.au

"Sander deWaal" wrote in message
...
"Robert Morein" said:


I only dared to push them up to 2.5A, still no match.
I feared launching them into orbit, so I stopped there.


Why? There's no thermal runaway. As long as they don't get too hot,
they'll
be OK.


I observed a slight increase in current with temperature, and my
heatsink was only 0.6 K/W ...... ;-)

They specifically have a negative temperature coefficient. Interesting
experiment to push it

Still didn't sound like the Hitachis, though.

Please remember that this experimental amp didn't have AC loop
feedback (just a DC servo loop).

--

- Never argue with idiots, they drag you down their level and beat you
with experience. -

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks
and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker)
and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp.
I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps,
metal
resistors, better pots etc. If I like the way the Mac sounds, would
it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The Hafler has
newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all
MOSFET amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin
time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would be
a much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They
cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up in
smoke. Late model PLs did not suffer this problem. In any case, there
are better choices, but I was trying to make a point about how bad both
amps mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not to
your taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time. Compression
is distortion. Distortion is bad.

I don't know of any quantifiable distortion, except for that which occurs as
the output voltage approaches the rails. That's pretty high up.

BTW, the Acoustat TNT-200,with "transnova" circuitry, came out about the
same time, and drives cleanly to the rails.

"François Yves Le Gal" wrote in message
...
On Mon, 27 Mar 2006 17:19:05 -0500, "Robert Morein"
wrote:

They specifically have a negative temperature coefficient. Interesting
experiment to push it

They don't. The typical tempco is *positive* : when temperature augments,
resistance augments. Part of the working zone shows a *negative* tempco,
with possible runaway problems leading to thermal destruction.

Thank you, I reversed a sign.


Suggested reading: "Thermal Instability of Low Voltage Power-MOSFETs",
Consoli, Alfio, et al, IEEE Transactions on Power Electronics, Volume 15,
No. 3, May 2000.

I don't have easy access to the journal. However, MOSFETs have quite a
spread of characteristics. Designers who used the original Hitachi devices
boasted that the outputs could be freely shorted. These earlier MOSFETs had
much higher "on" resistance. Perhaps the negative region is less significant
to device destruction than with newer devices.

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks
and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker)
and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110
preamp. I
know that the Mac was built to the highest standards of the mid
70s,
but even my Hafler, a modest piece of equipment, has poly caps,
metal
resistors, better pots etc. If I like the way the Mac sounds, would
it
be worthwhile or even desirable to upgrade individual components?
My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The Hafler
has newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all
MOSFET amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin
time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would be
a much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They
cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up in
smoke. Late model PLs did not suffer this problem. In any case, there
are better choices, but I was trying to make a point about how bad both
amps mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not to
your taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time. Compression
is distortion. Distortion is bad.

I don't know of any quantifiable distortion, except for that which occurs
as the output voltage approaches the rails. That's pretty high up.

**You said it yourself: "It sounds soft, perhaps not to your taste, but
"bad" ?" The "softness" you notice, is compression. Halfers possess an
exemplary frequency response, so that is not an issue. It is compression
distortion which is the problem. It can be heard on Perreaux amps, Haflers
and a whole host of others of the time.


BTW, the Acoustat TNT-200,with "transnova" circuitry, came out about the
same time, and drives cleanly to the rails.

**The Acoustat used MOSFETs? If they used them in a conventional fashion,
you could expect to see around 15 Volts dropped across the output devices.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a bricks
and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker)
and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110
preamp. I
know that the Mac was built to the highest standards of the mid
70s,
but even my Hafler, a modest piece of equipment, has poly caps,
metal
resistors, better pots etc. If I like the way the Mac sounds,
would it
be worthwhile or even desirable to upgrade individual components?
My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The Hafler
has newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all
MOSFET amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the coin
time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would
be a much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly. They
cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up
in smoke. Late model PLs did not suffer this problem. In any case,
there are better choices, but I was trying to make a point about how
bad both amps mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not to
your taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time.
Compression is distortion. Distortion is bad.

I don't know of any quantifiable distortion, except for that which occurs
as the output voltage approaches the rails. That's pretty high up.

**You said it yourself: "It sounds soft, perhaps not to your taste, but
"bad" ?" The "softness" you notice, is compression. Halfers possess an
exemplary frequency response, so that is not an issue. It is compression
distortion which is the problem. It can be heard on Perreaux amps, Haflers
and a whole host of others of the time.

It compresses as the voltage reaches the rails. The result is an ideal
clipping characteristic. I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful characteristic.
I can drive one of the classic Hafler amps with a source that has a very
high peak-to-crest ratio, such as certain piano music. At high volumes, any
other amp exhibits some audible clipping. The Hafler, never.

BTW, the Acoustat TNT-200,with "transnova" circuitry, came out about the
same time, and drives cleanly to the rails.

**The Acoustat used MOSFETs? If they used them in a conventional fashion,
you could expect to see around 15 Volts dropped across the output devices.

Where do you get 15 volts? It depends upon exactly what the load is.

Outputs are 2SK135 & 2SJ50, three each per channel. I have five of them;
they are my all-time favorite amp. None of the "MOSFET mist"; half power to
400 kHz, slew rate 165 volts/us, damping factor 1000 at 20kHz. The
circuit is like no other; the output sources are grounded, while the drains
swing the entire rectifier bridge for DC, while AC is coupled by the power
supply electrolytics and a bypass network. According to Strickland, the
output stage has both voltage gain of 10 and current gain of 500. It is a
difficult circuit to comprehend; Rich Hollis, who fixed one of mine, had to
input the entire circuit into SPICE in order to determine how it should
behave.

The amp is built on a chassis made of 300 stainless, spot-welded together.

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a
bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a
breaker) and
it will be a few days before I can put it in my system and make
an
evaluation. I currently have a Hafler 220 amp and Hafler 110
preamp. I
know that the Mac was built to the highest standards of the mid
70s,
but even my Hafler, a modest piece of equipment, has poly caps,
metal
resistors, better pots etc. If I like the way the Mac sounds,
would it
be worthwhile or even desirable to upgrade individual
components? My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The Hafler
has newer semiconductors. Rapid progress was made in those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all
MOSFET amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the
coin time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear would
be a much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly.
They cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had stability
problems, if retro-fitted with fast(er) output devices. They went up
in smoke. Late model PLs did not suffer this problem. In any case,
there are better choices, but I was trying to make a point about how
bad both amps mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not to
your taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time.
Compression is distortion. Distortion is bad.

I don't know of any quantifiable distortion, except for that which
occurs as the output voltage approaches the rails. That's pretty high
up.

**You said it yourself: "It sounds soft, perhaps not to your taste, but
"bad" ?" The "softness" you notice, is compression. Halfers possess an
exemplary frequency response, so that is not an issue. It is compression
distortion which is the problem. It can be heard on Perreaux amps,
Haflers and a whole host of others of the time.

It compresses as the voltage reaches the rails.

**Perhaps, but that is not what makes it "soft" throughout the rest of the
range.

With respect to compression, I have to dispute. Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier compressed
a full power sine wave, the result would not be a sine wave. The distorted
sine wave would be decomposable into a Fourier series with higher powers.
The extreme of this form of compression results in something approximating a
square wave. Please explain how an amplifier can compress while having
excellent harmonic distortion.

Because of gate capacitance and on resistance, MOSFETS do compress, but in
order to meet rated distortion at rated power, they do this at power levels
above the rated power. This is not an egregious flaw; the amp lacks headroom
in a manner similar to Class A amplifiers. But the classic MOSFET design
also provides a benefit similar to pure Class A bipolar amps; extremely low
distortion at low power.

The result is an ideal
clipping characteristic.

**Sort of.

I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful
characteristic. I can drive one of the classic Hafler amps with a source
that has a very high peak-to-crest ratio, such as certain piano music. At
high volumes, any other amp exhibits some audible clipping.

**Nope. Haflers are no different to many other amps, WRT clipping. Clip
them hard and they sound harsh and nasty. Possibly less so than many amps,
but nasty, nevertheless. BTW: There are many other schemes which exist to
keep an amp (BJT) from exhibint unpleasant clipping characteristics. Most
involve sacrificing a few Volts of headroom. NAD is one such promoter of
"soft clipping" type systems. There are others. They cost a little more,
but can provide demonstable benefits. The best systems keep the
anti-clipping system outside the feedback loop.

The Hafler, never.

I have a NAD PE receiver, and my perception is that it does not clip as
cleanly as a Hafler. When driving Acoustat panels with a DH-200 or XL-280, a
deliberate twist of the volume knob full clockwise (which the Acoustats can
tolerate, they're rated at 117db), produces no audible clipping. The
amplifier has to clip, but does not manifest a typical clipping signature.
In mentioning Hafler, I specifically mean only those based on the original
Hafler design: the DH and XL models. When Rockford bought Hafler, and then
Acoustat, they eventually replaced the original Hafler design completely
with the Transnova circuitry. As much as I like them, these amplifiers do
clip audibly, because they do drive the MOSFETs straight to the rails.

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in
message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a
bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a
breaker) and
it will be a few days before I can put it in my system and make
an
evaluation. I currently have a Hafler 220 amp and Hafler 110
preamp. I
know that the Mac was built to the highest standards of the mid
70s,
but even my Hafler, a modest piece of equipment, has poly caps,
metal
resistors, better pots etc. If I like the way the Mac sounds,
would it
be worthwhile or even desirable to upgrade individual
components? My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The
Hafler has newer semiconductors. Rapid progress was made in
those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly
implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all
MOSFET amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the
coin time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear
would be a much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so many
amplifiers of one brand blown up or caught on fire so regularly.
They cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had
stability problems, if retro-fitted with fast(er) output devices.
They went up in smoke. Late model PLs did not suffer this problem.
In any case, there are better choices, but I was trying to make a
point about how bad both amps mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not
to your taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time.
Compression is distortion. Distortion is bad.

I don't know of any quantifiable distortion, except for that which
occurs as the output voltage approaches the rails. That's pretty high
up.

**You said it yourself: "It sounds soft, perhaps not to your taste,
but "bad" ?" The "softness" you notice, is compression. Halfers possess
an exemplary frequency response, so that is not an issue. It is
compression distortion which is the problem. It can be heard on
Perreaux amps, Haflers and a whole host of others of the time.

It compresses as the voltage reaches the rails.

**Perhaps, but that is not what makes it "soft" throughout the rest of
the range.

With respect to compression, I have to dispute.

**It's OK. Most do, when I present them with that information. However, it
is the ONLY explanation which makes sense of the "softness" associated with
Haflers, Perreaux and other early, standard MOSFET amps. Even with the level
WAY below clipping, even a crappy BJT amp (like a late model Phase Linear)
the lack of dynamics in the MOSFET amps is immediately noticable. You,
yourself, have acknowledged in your statement that they are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine wave.

**Except that I am not talking about sine waves. I am talking about fast
rise time, assymetrical transients. Just likke the stuff we get in music.
The Hafler does a fine job of reproducing sine waves, just like any other
MOSFET amp. It's music that it stuggles with.

The distorted
sine wave would be decomposable into a Fourier series with higher powers.
The extreme of this form of compression results in something approximating
a square wave. Please explain how an amplifier can compress while having
excellent harmonic distortion.

**Er, because it can.


Because of gate capacitance and on resistance, MOSFETS do compress,

**Their compression, I believe is more to do with the negative Tempco of Gm.

but in
order to meet rated distortion at rated power, they do this at power
levels above the rated power. This is not an egregious flaw; the amp lacks
headroom in a manner similar to Class A amplifiers. But the classic MOSFET
design also provides a benefit similar to pure Class A bipolar amps;
extremely low distortion at low power.

**Only because it uses massive amounts of Global NFB. Due to the high levels
of distortion at low currents, MOSFETs need to be biased on real hard, or be
used with huge amounts of NFB (usually Global). Except for very high bias
designs, there are no (to the best of my knowledge) Zero Global NFB MOSFET
amps.


The result is an ideal
clipping characteristic.

**Sort of.

I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful
characteristic. I can drive one of the classic Hafler amps with a source
that has a very high peak-to-crest ratio, such as certain piano music.
At high volumes, any other amp exhibits some audible clipping.

**Nope. Haflers are no different to many other amps, WRT clipping. Clip
them hard and they sound harsh and nasty. Possibly less so than many
amps, but nasty, nevertheless. BTW: There are many other schemes which
exist to keep an amp (BJT) from exhibint unpleasant clipping
characteristics. Most involve sacrificing a few Volts of headroom. NAD is
one such promoter of "soft clipping" type systems. There are others. They
cost a little more, but can provide demonstable benefits. The best
systems keep the anti-clipping system outside the feedback loop.

The Hafler, never.

I have a NAD PE receiver, and my perception is that it does not clip as
cleanly as a Hafler.

**Which model? ALL of the PE NADs are utter horrors. They clip badly. Soft
clipping notwithstanding. In any case, I used the NAD as an exmaple. The NAD
scheme is primitive and not all that good, but it does work. NADs clip more
gracefully than most of their competition.

When driving Acoustat panels with a DH-200 or XL-280, a
deliberate twist of the volume knob full clockwise (which the Acoustats
can tolerate, they're rated at 117db), produces no audible clipping. The
amplifier has to clip, but does not manifest a typical clipping signature.
In mentioning Hafler, I specifically mean only those based on the
original Hafler design: the DH and XL models. When Rockford bought Hafler,
and then Acoustat, they eventually replaced the original Hafler design
completely with the Transnova circuitry. As much as I like them, these
amplifiers do clip audibly, because they do drive the MOSFETs straight to
the rails.

**They use a higher Voltage rail for the drivers?


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in
message
...

"Robert Morein" wrote in message
...

wrote in message
ups.com...
I just bought a clean Macintosh MA 6100 integrated amp at a
bricks and
motar auction. I haven't done anything with the 6100 other
than
plugging it in (all the lights work and it didn't blow a
breaker) and
it will be a few days before I can put it in my system and
make an
evaluation. I currently have a Hafler 220 amp and Hafler 110
preamp. I
know that the Mac was built to the highest standards of the
mid 70s,
but even my Hafler, a modest piece of equipment, has poly
caps, metal
resistors, better pots etc. If I like the way the Mac sounds,
would it
be worthwhile or even desirable to upgrade individual
components? My
system is two channel, music only and I listen to FM, CDs and
records.

Don't assume that the Mac can be made to sound better. The
Hafler has newer semiconductors. Rapid progress was made in
those years.

**Not so much. The Hafler uses MSOFETs. Rather poorly
implemented.

I disagree. The Hafler can sound pretty good, matched with bright
speakers.

**Nope. The Hafler has the typical compressed sound quality of all
MOSFET amps of it's time. The XL280 was better.


The Mac,
however, uses BJTs, but is crippled in other ways. Toss of the
coin time.

I'd agree with that.

They're both pretty ordinary amps. A late model Phase Linear
would be a much better (and cheaper) choice.

The Phase Linears are nicknamed "Flame Linear". Never have so
many amplifiers of one brand blown up or caught on fire so
regularly. They cannot be recommended for any use.

**I did say: LATE MODEL Phase Linears. Early model PLs had
stability problems, if retro-fitted with fast(er) output devices.
They went up in smoke. Late model PLs did not suffer this problem.
In any case, there are better choices, but I was trying to make a
point about how bad both amps mentioned actually are.

What have you got against the DH-220 ? It sounds soft, perhaps not
to your taste, but "bad" ?

**It compresses the sound, like all MOSFET amps of it's time.
Compression is distortion. Distortion is bad.

I don't know of any quantifiable distortion, except for that which
occurs as the output voltage approaches the rails. That's pretty high
up.

**You said it yourself: "It sounds soft, perhaps not to your taste,
but "bad" ?" The "softness" you notice, is compression. Halfers
possess an exemplary frequency response, so that is not an issue. It
is compression distortion which is the problem. It can be heard on
Perreaux amps, Haflers and a whole host of others of the time.

It compresses as the voltage reaches the rails.

**Perhaps, but that is not what makes it "soft" throughout the rest of
the range.

With respect to compression, I have to dispute.

**It's OK. Most do, when I present them with that information. However, it
is the ONLY explanation which makes sense of the "softness" associated
with Haflers, Perreaux and other early, standard MOSFET amps. Even with
the level WAY below clipping, even a crappy BJT amp (like a late model
Phase Linear) the lack of dynamics in the MOSFET amps is immediately
noticable. You, yourself, have acknowledged in your statement that they
are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine wave.

**Except that I am not talking about sine waves. I am talking about fast
rise time, assymetrical transients. Just likke the stuff we get in music.
The Hafler does a fine job of reproducing sine waves, just like any other
MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I would
need to see a gapless explanation. Your conjecture might be right, but
there's so much of that in this backwater field. In order to explain why a
classic MOSFET design can reproduce high amplitude sine waves but not
transients, if in fact that's what happening, some more work has to be done.
A good explanation doesn't mix the various possibilities together; it
separates them out. Nelson Pass says, "
The Mosfet designs on the market are also Class AB designs. The transfer
curve of Mosfets reveals serious nonlinearities at low bias

currents, resulting in crossover nonlinearity in push-pull designs. This
design flaw makes for a sonic signature that many have referred to as

"Mosfet mist", where a loss of detail is apparent."

His explanation is different from yours; it is unlikely that both
explanations would contribute in approximately equal proportions. And he
isn't necessarily right. Here's my own personal anecdote.

The Hafler XL-280 is an improved version of the DH-200/220, but it looks
very similar. It has six output devices/channel; the bias current is the
same 100ma/device, it has JFET inputs, but it looks pretty much the same --
except that there is a small air plate varicap in the output. This is/was to
be used with a comparator bridge lent by the dealer to null the difference
between the amp input and output. I've played with it, although recently,
I've left it untouched. The amp is flat far above the audible range, with a
slewing rate of 75 v/us, but it is said to have a peak at 170 kHz, adjusted
by the cap. This amplifier does not have the liquid mist of a DH-200; at
least one review, perhaps Audio, stated that it had the greatest amount of
low level detail of any amp they had heard. Nevertheless, the amplifier does
sound a little flat, or undynamic.

But when the amps are bridged, the sound changes completely. I use a pair
with the NEAR 50m's. In bridged mode, they sound like a very, very good
amplifier. What happens when an amplifier is bridged? Does the damping
factor halve? The XL-280 has a larger cousin, the XL-600, with a similar
circuit, the same air varicap, and 8 devices/channel, run at 100ma/device.
It has a damping factor of 80, approximately half that of the XL-280. The
XL-600 has enjoyed considerable popularity in U.S. studios, as a very good
all-around amp. It sounds indistingushable from the bridged XL-280's. I have
both in my rack, but I use the 280's in the winter, because they have no
fan.

I wen through the above to show that the MOSFET mist, which still afflicts
certain modern designs, such as the ADCOM pieces, can apparently be
diminished or eliminated to the point where the result is considered highly
desirable, at least by some ears, while still maintaining the traditional
zero-voltage gain output stage.


The distorted
sine wave would be decomposable into a Fourier series with higher powers.
The extreme of this form of compression results in something
approximating a square wave. Please explain how an amplifier can compress
while having excellent harmonic distortion.

**Er, because it can.

Did I see your hands wave? Please say that again with your hands in your
pockets


Because of gate capacitance and on resistance, MOSFETS do compress,

**Their compression, I believe is more to do with the negative Tempco of
Gm.

but in
order to meet rated distortion at rated power, they do this at power
levels above the rated power. This is not an egregious flaw; the amp
lacks headroom in a manner similar to Class A amplifiers. But the classic
MOSFET design also provides a benefit similar to pure Class A bipolar
amps; extremely low distortion at low power.

**Only because it uses massive amounts of Global NFB. Due to the high
levels of distortion at low currents, MOSFETs need to be biased on real
hard, or be used with huge amounts of NFB (usually Global). Except for
very high bias designs, there are no (to the best of my knowledge) Zero
Global NFB MOSFET amps.


The result is an ideal
clipping characteristic.

**Sort of.

I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful
characteristic. I can drive one of the classic Hafler amps with a
source that has a very high peak-to-crest ratio, such as certain piano
music. At high volumes, any other amp exhibits some audible clipping.

**Nope. Haflers are no different to many other amps, WRT clipping. Clip
them hard and they sound harsh and nasty. Possibly less so than many
amps, but nasty, nevertheless. BTW: There are many other schemes which
exist to keep an amp (BJT) from exhibint unpleasant clipping
characteristics. Most involve sacrificing a few Volts of headroom. NAD
is one such promoter of "soft clipping" type systems. There are others.
They cost a little more, but can provide demonstable benefits. The best
systems keep the anti-clipping system outside the feedback loop.

The Hafler, never.

I have a NAD PE receiver, and my perception is that it does not clip as
cleanly as a Hafler.

**Which model?

7225PE

ALL of the PE NADs are utter horrors. They clip badly. Soft
clipping notwithstanding. In any case, I used the NAD as an exmaple. The
NAD scheme is primitive and not all that good, but it does work. NADs clip
more gracefully than most of their competition.

When driving Acoustat panels with a DH-200 or XL-280, a
deliberate twist of the volume knob full clockwise (which the Acoustats
can tolerate, they're rated at 117db), produces no audible clipping. The
amplifier has to clip, but does not manifest a typical clipping
signature. In mentioning Hafler, I specifically mean only those based on
the original Hafler design: the DH and XL models. When Rockford bought
Hafler, and then Acoustat, they eventually replaced the original Hafler
design completely with the Transnova circuitry. As much as I like them,
these amplifiers do clip audibly, because they do drive the MOSFETs
straight to the rails.

**They use a higher Voltage rail for the drivers?

The rail voltage in the Transnova is 72V. However, because the outputs have
voltage gain, the drivers are operated from a regulated 25V rail.

"François Yves Le Gal" wrote in message
...
On Mon, 27 Mar 2006 19:06:26 -0500, "Robert Morein"
wrote:

Designers who used the original Hitachi devices
boasted that the outputs could be freely shorted.

I doubt that engineers boasted this. Sounds more like yet another
marketing
gimmick.

You should understand that a Mosfet isn't a single transistor: it's die is
made of multiple elementary cells connected in parallel (hence the highish
input capacitance among other characteristics).

Yes, I know this.

If you go outside the SOA,
thermal regulation won't be instantaneous - temperature has to rise on the
whole die, which displays a non negligible thermal inertia - and some or
all
cells can thus be destroyed.

I understand this; your references are very informative, but I do not yet
reach the conclusion that all MOSFETs are practically susceptible to this
effect with respect to audio applications. Your references do make it clear
that they should not be deliberately shorted.

Perhaps the negative region is less significant
to device destruction than with newer devices.

It's nearly the same.
Your reference contradicts that. Quoting, "Use of a very?low?on?resistance
device offers low losses for steady?state operation but may cause the device
to fail during a short circuit or an overload."
This remark suggests that the older devices are, indeed, more resistant.

When the operating point is set at low currents, negative tempco is very
real. See for instance fig. 4 in
http://www.eetasia.com/ARTICLES/2005...N23_EMD_AN.PDF, which
deals
with Mosfets used in hot-swap controllers, but the underlying theory also
applies to an audio context.

It's a good reference, but it was obviously authored with reference to
current devices, not antiques. Also, Sander was trying to bias a MOSFET,
which, presumably had a standard audio load, or open circuit output. The
paper specifically states that the sign of the temperature coefficient is
dependent on the gate to source voltage. I do not see an obvious answer to
the question of whether it is possible to bias an older Hitachi device into
thermal runaway, as related to Sander's activity.

BTW, thanks for the references. They are useful, and I will take note of
them.

"Robert Morein" said:


It's a good reference, but it was obviously authored with reference to
current devices, not antiques. Also, Sander was trying to bias a MOSFET,
which, presumably had a standard audio load, or open circuit output. The
paper specifically states that the sign of the temperature coefficient is
dependent on the gate to source voltage. I do not see an obvious answer to
the question of whether it is possible to bias an older Hitachi device into
thermal runaway, as related to Sander's activity.


For the record, the experiment I wrote about was with the BUZ900/905
devices.

In the past, I determined the optimal bias current for the Hitachis
the same way, and I didn't notice the slight bias drift upwards with
rising temperature. I only went to 1 amp per device, though.

--

- Never argue with idiots, they drag you down their level and beat you with experience. -

"Robert Morein" wrote in message
news

SNIP

**It's OK. Most do, when I present them with that information. However,
it is the ONLY explanation which makes sense of the "softness" associated
with Haflers, Perreaux and other early, standard MOSFET amps. Even with
the level WAY below clipping, even a crappy BJT amp (like a late model
Phase Linear) the lack of dynamics in the MOSFET amps is immediately
noticable. You, yourself, have acknowledged in your statement that they
are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine wave.

**Except that I am not talking about sine waves. I am talking about fast
rise time, assymetrical transients. Just likke the stuff we get in music.
The Hafler does a fine job of reproducing sine waves, just like any other
MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I would
need to see a gapless explanation.

**OK. I'll try to explain later. Briefly, however, consider the effects, at
chip level, when a MOSFET is subject to the heating via a fast rising
transient (which causes lots of current to flow). The MOSFET very briefly
tends to reduce this current, via the negative tempco of Gm. The NFB loop
will tend to counteract this effect to some degree, but, IMO, not all that
successfully. Very high bias designs (ala Pass, et al) get around this
problem by operating the chip at constant high temps. Thus, the effect is
not noticable. Low bias MOSFET amps do suffer with this compression effect.
Sound reasonable?

Your conjecture might be right, but
there's so much of that in this backwater field. In order to explain why a
classic MOSFET design can reproduce high amplitude sine waves but not
transients, if in fact that's what happening, some more work has to be
done. A good explanation doesn't mix the various possibilities together;
it separates them out. Nelson Pass says, "
The Mosfet designs on the market are also Class AB designs. The transfer
curve of Mosfets reveals serious nonlinearities at low bias

**Which is exactly what I said further down the thread. The 'knee' of
MOSFETs is much higher than that of BJTs, yet MOSFETs are rarely operated
with significantly more bias current than BJTs. A critical failure IMO.


currents, resulting in crossover nonlinearity in push-pull designs. This
design flaw makes for a sonic signature that many have referred to as

"Mosfet mist", where a loss of detail is apparent."

His explanation is different from yours; it is unlikely that both
explanations would contribute in approximately equal proportions. And he
isn't necessarily right. Here's my own personal anecdote.

**Perhaps, but I happen to think he is on the money. MOSFETs operating at
elevated bias currents DO sound pretty decent. They do not have the
compression effects I note with low bias designs. They also sound notably
cleaner and more articulate. As good, in fact, as a decent BJT deisgn
operating at significantly lower bias currents.


The Hafler XL-280 is an improved version of the DH-200/220, but it looks
very similar. It has six output devices/channel; the bias current is the
same 100ma/device, it has JFET inputs, but it looks pretty much the
same -- except that there is a small air plate varicap in the output.
This is/was to be used with a comparator bridge lent by the dealer to null
the difference between the amp input and output. I've played with it,
although recently, I've left it untouched. The amp is flat far above the
audible range, with a slewing rate of 75 v/us, but it is said to have a
peak at 170 kHz, adjusted by the cap. This amplifier does not have the
liquid mist of a DH-200; at least one review, perhaps Audio, stated that
it had the greatest amount of low level detail of any amp they had heard.
Nevertheless, the amplifier does sound a little flat, or undynamic.

**Of course. It is a low bias, conventional MOSFET amp. They're all very
similar in my experience.


But when the amps are bridged, the sound changes completely. I use a pair
with the NEAR 50m's. In bridged mode, they sound like a very, very good
amplifier. What happens when an amplifier is bridged? Does the damping
factor halve?

**Yep. Along with a bunch of other problems and advantages. Personally, I
have serious issues with most bridged amps. Mainly because, at clipping, the
results are extremely unpridictable. Damping factors SEEMS to drop to zero
in many amps. Perhaps it is the fact that the amps can never be absolutely
perfectly matched and problems arise due to that. I'm not certain, but
bridging amps seems to improve the dynamic abilities, but it also seems to
introduce other problems which may be worse to many listeners.

The XL-280 has a larger cousin, the XL-600, with a similar
circuit, the same air varicap, and 8 devices/channel, run at 100ma/device.
It has a damping factor of 80, approximately half that of the XL-280. The
XL-600 has enjoyed considerable popularity in U.S. studios, as a very good
all-around amp. It sounds indistingushable from the bridged XL-280's. I
have both in my rack, but I use the 280's in the winter, because they have
no fan.

I wen through the above to show that the MOSFET mist, which still afflicts
certain modern designs, such as the ADCOM pieces, can apparently be
diminished or eliminated to the point where the result is considered
highly desirable, at least by some ears, while still maintaining the
traditional zero-voltage gain output stage.


The distorted
sine wave would be decomposable into a Fourier series with higher
powers. The extreme of this form of compression results in something
approximating a square wave. Please explain how an amplifier can
compress while having excellent harmonic distortion.

**Er, because it can.

Did I see your hands wave? Please say that again with your hands in your
pockets

**Sorry. I couldn't resist.



Because of gate capacitance and on resistance, MOSFETS do compress,

**Their compression, I believe is more to do with the negative Tempco of
Gm.

but in
order to meet rated distortion at rated power, they do this at power
levels above the rated power. This is not an egregious flaw; the amp
lacks headroom in a manner similar to Class A amplifiers. But the
classic MOSFET design also provides a benefit similar to pure Class A
bipolar amps; extremely low distortion at low power.

**Only because it uses massive amounts of Global NFB. Due to the high
levels of distortion at low currents, MOSFETs need to be biased on real
hard, or be used with huge amounts of NFB (usually Global). Except for
very high bias designs, there are no (to the best of my knowledge) Zero
Global NFB MOSFET amps.


The result is an ideal
clipping characteristic.

**Sort of.

I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful
characteristic. I can drive one of the classic Hafler amps with a
source that has a very high peak-to-crest ratio, such as certain piano
music. At high volumes, any other amp exhibits some audible clipping.

**Nope. Haflers are no different to many other amps, WRT clipping. Clip
them hard and they sound harsh and nasty. Possibly less so than many
amps, but nasty, nevertheless. BTW: There are many other schemes which
exist to keep an amp (BJT) from exhibint unpleasant clipping
characteristics. Most involve sacrificing a few Volts of headroom. NAD
is one such promoter of "soft clipping" type systems. There are others.
They cost a little more, but can provide demonstable benefits. The best
systems keep the anti-clipping system outside the feedback loop.

The Hafler, never.

I have a NAD PE receiver, and my perception is that it does not clip as
cleanly as a Hafler.

**Which model?

7225PE

**AHA! Note the PE moniker. They are sonic disasters. All of them. The
clipping characteristic can be utterly appalling in the PE designs. Try it
sometime (not connected to speakers!). Connect to a dummy load, hang a
'scope off the end and crank the volume up to clipping. When the high
Voltage power supply shuts off, the amp falls into VERY severe clipping and
the resultant sound is terrible, as is the potential for speaker damage.


ALL of the PE NADs are utter horrors. They clip badly. Soft
clipping notwithstanding. In any case, I used the NAD as an exmaple. The
NAD scheme is primitive and not all that good, but it does work. NADs
clip more gracefully than most of their competition.

When driving Acoustat panels with a DH-200 or XL-280, a
deliberate twist of the volume knob full clockwise (which the Acoustats
can tolerate, they're rated at 117db), produces no audible clipping. The
amplifier has to clip, but does not manifest a typical clipping
signature. In mentioning Hafler, I specifically mean only those based
on the original Hafler design: the DH and XL models. When Rockford
bought Hafler, and then Acoustat, they eventually replaced the original
Hafler design completely with the Transnova circuitry. As much as I like
them, these amplifiers do clip audibly, because they do drive the
MOSFETs straight to the rails.

**They use a higher Voltage rail for the drivers?

The rail voltage in the Transnova is 72V. However, because the outputs
have voltage gain, the drivers are operated from a regulated 25V rail.

**Interesting. Do you mean that the drivers are operated from a supply which
is operating 25 Volts ABOVE the 72 Volts?


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
news

SNIP

**It's OK. Most do, when I present them with that information. However,
it is the ONLY explanation which makes sense of the "softness"
associated with Haflers, Perreaux and other early, standard MOSFET amps.
Even with the level WAY below clipping, even a crappy BJT amp (like a
late model Phase Linear) the lack of dynamics in the MOSFET amps is
immediately noticable. You, yourself, have acknowledged in your
statement that they are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine wave.

**Except that I am not talking about sine waves. I am talking about fast
rise time, assymetrical transients. Just likke the stuff we get in
music. The Hafler does a fine job of reproducing sine waves, just like
any other MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I would
need to see a gapless explanation.

**OK. I'll try to explain later. Briefly, however, consider the effects,
at chip level, when a MOSFET is subject to the heating via a fast rising
transient (which causes lots of current to flow). The MOSFET very briefly
tends to reduce this current, via the negative tempco of Gm. The NFB loop
will tend to counteract this effect to some degree, but, IMO, not all that
successfully. Very high bias designs (ala Pass, et al) get around this
problem by operating the chip at constant high temps. Thus, the effect is
not noticable. Low bias MOSFET amps do suffer with this compression
effect. Sound reasonable?

Not proven, but definitely reasonable, ie., within consideration. But if we
listen to Francois, low-biased MOSFETs may be in the negative temperature
coefficient region.

Your conjecture might be right, but
there's so much of that in this backwater field. In order to explain why
a classic MOSFET design can reproduce high amplitude sine waves but not
transients, if in fact that's what happening, some more work has to be
done. A good explanation doesn't mix the various possibilities together;
it separates them out. Nelson Pass says, "
The Mosfet designs on the market are also Class AB designs. The transfer
curve of Mosfets reveals serious nonlinearities at low bias

**Which is exactly what I said further down the thread. The 'knee' of
MOSFETs is much higher than that of BJTs, yet MOSFETs are rarely operated
with significantly more bias current than BJTs. A critical failure IMO.


currents, resulting in crossover nonlinearity in push-pull designs. This
design flaw makes for a sonic signature that many have referred to as

"Mosfet mist", where a loss of detail is apparent."

His explanation is different from yours; it is unlikely that both
explanations would contribute in approximately equal proportions. And he
isn't necessarily right. Here's my own personal anecdote.

**Perhaps, but I happen to think he is on the money. MOSFETs operating at
elevated bias currents DO sound pretty decent. They do not have the
compression effects I note with low bias designs. They also sound notably
cleaner and more articulate. As good, in fact, as a decent BJT deisgn
operating at significantly lower bias currents.


The Hafler XL-280 is an improved version of the DH-200/220, but it looks
very similar. It has six output devices/channel; the bias current is the
same 100ma/device, it has JFET inputs, but it looks pretty much the
same -- except that there is a small air plate varicap in the output.
This is/was to be used with a comparator bridge lent by the dealer to
null the difference between the amp input and output. I've played with
it, although recently, I've left it untouched. The amp is flat far above
the audible range, with a slewing rate of 75 v/us, but it is said to have
a peak at 170 kHz, adjusted by the cap. This amplifier does not have the
liquid mist of a DH-200; at least one review, perhaps Audio, stated that
it had the greatest amount of low level detail of any amp they had heard.
Nevertheless, the amplifier does sound a little flat, or undynamic.

**Of course. It is a low bias, conventional MOSFET amp. They're all very
similar in my experience.


But when the amps are bridged, the sound changes completely. I use a pair
with the NEAR 50m's. In bridged mode, they sound like a very, very good
amplifier. What happens when an amplifier is bridged? Does the damping
factor halve?

**Yep. Along with a bunch of other problems and advantages. Personally, I
have serious issues with most bridged amps. Mainly because, at clipping,
the results are extremely unpridictable. Damping factors SEEMS to drop to
zero in many amps. Perhaps it is the fact that the amps can never be
absolutely perfectly matched and problems arise due to that. I'm not
certain, but bridging amps seems to improve the dynamic abilities, but it
also seems to introduce other problems which may be worse to many
listeners.

The XL-280 has a larger cousin, the XL-600, with a similar
circuit, the same air varicap, and 8 devices/channel, run at
100ma/device. It has a damping factor of 80, approximately half that of
the XL-280. The XL-600 has enjoyed considerable popularity in U.S.
studios, as a very good all-around amp. It sounds indistingushable from
the bridged XL-280's. I have both in my rack, but I use the 280's in the
winter, because they have no fan.

I wen through the above to show that the MOSFET mist, which still
afflicts certain modern designs, such as the ADCOM pieces, can apparently
be diminished or eliminated to the point where the result is considered
highly desirable, at least by some ears, while still maintaining the
traditional zero-voltage gain output stage.


The distorted
sine wave would be decomposable into a Fourier series with higher
powers. The extreme of this form of compression results in something
approximating a square wave. Please explain how an amplifier can
compress while having excellent harmonic distortion.

**Er, because it can.

Did I see your hands wave? Please say that again with your hands in your
pockets

**Sorry. I couldn't resist.



Because of gate capacitance and on resistance, MOSFETS do compress,

**Their compression, I believe is more to do with the negative Tempco of
Gm.

but in
order to meet rated distortion at rated power, they do this at power
levels above the rated power. This is not an egregious flaw; the amp
lacks headroom in a manner similar to Class A amplifiers. But the
classic MOSFET design also provides a benefit similar to pure Class A
bipolar amps; extremely low distortion at low power.

**Only because it uses massive amounts of Global NFB. Due to the high
levels of distortion at low currents, MOSFETs need to be biased on real
hard, or be used with huge amounts of NFB (usually Global). Except for
very high bias designs, there are no (to the best of my knowledge) Zero
Global NFB MOSFET amps.


The result is an ideal
clipping characteristic.

**Sort of.

I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful
characteristic. I can drive one of the classic Hafler amps with a
source that has a very high peak-to-crest ratio, such as certain
piano music. At high volumes, any other amp exhibits some audible
clipping.

**Nope. Haflers are no different to many other amps, WRT clipping.
Clip them hard and they sound harsh and nasty. Possibly less so than
many amps, but nasty, nevertheless. BTW: There are many other schemes
which exist to keep an amp (BJT) from exhibint unpleasant clipping
characteristics. Most involve sacrificing a few Volts of headroom. NAD
is one such promoter of "soft clipping" type systems. There are
others. They cost a little more, but can provide demonstable benefits.
The best systems keep the anti-clipping system outside the feedback
loop.

The Hafler, never.

I have a NAD PE receiver, and my perception is that it does not clip as
cleanly as a Hafler.

**Which model?

7225PE

**AHA! Note the PE moniker. They are sonic disasters. All of them. The
clipping characteristic can be utterly appalling in the PE designs. Try it
sometime (not connected to speakers!). Connect to a dummy load, hang a
'scope off the end and crank the volume up to clipping. When the high
Voltage power supply shuts off, the amp falls into VERY severe clipping
and the resultant sound is terrible, as is the potential for speaker
damage.


ALL of the PE NADs are utter horrors. They clip badly. Soft
clipping notwithstanding. In any case, I used the NAD as an exmaple. The
NAD scheme is primitive and not all that good, but it does work. NADs
clip more gracefully than most of their competition.

When driving Acoustat panels with a DH-200 or XL-280, a
deliberate twist of the volume knob full clockwise (which the Acoustats
can tolerate, they're rated at 117db), produces no audible clipping.
The amplifier has to clip, but does not manifest a typical clipping
signature. In mentioning Hafler, I specifically mean only those based
on the original Hafler design: the DH and XL models. When Rockford
bought Hafler, and then Acoustat, they eventually replaced the original
Hafler design completely with the Transnova circuitry. As much as I
like them, these amplifiers do clip audibly, because they do drive the
MOSFETs straight to the rails.

**They use a higher Voltage rail for the drivers?

The rail voltage in the Transnova is 72V. However, because the outputs
have voltage gain, the drivers are operated from a regulated 25V rail.

**Interesting. Do you mean that the drivers are operated from a supply
which is operating 25 Volts ABOVE the 72 Volts?

No, actually 25V referenced to zero. Since the outputs have voltage gain,
they do not have to be driven at full voltage like conventional voltage
followers.

--
Trevor Wilson
www.rageaudio.com.au
Trevor, you definitely have a point to consider.. Like everything else in
this underfunded business, there is no economic motivation to really nail
it down, like stress factors in a wide-body jet. Since I have two bridged
MOSFET amps, and an XL-600, both with conventional voltage-follower
circuitry, that don't have the characteristic MOSFET mist, I'm not
convinced, nor do I dismiss your theory. Could the Excelinear circuit be a
cheap trick that fools the ear into thinking there is no "mist" present?
Perhaps.

And the ADCOM HEXFET amps, designed by John Curl, who we have just
referenced, have a horrible case of "mist". Bad amps. Waste of iron and
silicon.

BTW, the original Transnova circuit, as implemented in the Acoustat, has
only three stages. The first two are JFETs. The reduction in number of
stages, and the speed of the devices permits an increase in the amount of
feedback. These amplifiers have remarkable clarity, even though the output
coupling is almost bizarre, and massive feedback (which Strickland claims
also incorporates positive, or complementary) may be the thing which
overcomes whatever it is in MOSFETs that has to be overcome.

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
news

SNIP

**It's OK. Most do, when I present them with that information. However,
it is the ONLY explanation which makes sense of the "softness"
associated with Haflers, Perreaux and other early, standard MOSFET
amps. Even with the level WAY below clipping, even a crappy BJT amp
(like a late model Phase Linear) the lack of dynamics in the MOSFET
amps is immediately noticable. You, yourself, have acknowledged in your
statement that they are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine
wave.

**Except that I am not talking about sine waves. I am talking about
fast rise time, assymetrical transients. Just likke the stuff we get in
music. The Hafler does a fine job of reproducing sine waves, just like
any other MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I
would need to see a gapless explanation.

**OK. I'll try to explain later. Briefly, however, consider the effects,
at chip level, when a MOSFET is subject to the heating via a fast rising
transient (which causes lots of current to flow). The MOSFET very briefly
tends to reduce this current, via the negative tempco of Gm. The NFB loop
will tend to counteract this effect to some degree, but, IMO, not all
that successfully. Very high bias designs (ala Pass, et al) get around
this problem by operating the chip at constant high temps. Thus, the
effect is not noticable. Low bias MOSFET amps do suffer with this
compression effect. Sound reasonable?

Not proven, but definitely reasonable, ie., within consideration. But if
we listen to Francois, low-biased MOSFETs may be in the negative
temperature coefficient region.

**Absolutely, which is why for MOSFETs to sound reasonable, they MUST be
biased on hard. Very hard. At least ten times harder than a BJT. And then,
all you get is a linearity which is approximately similar to a BJT.


Your conjecture might be right, but
there's so much of that in this backwater field. In order to explain why
a classic MOSFET design can reproduce high amplitude sine waves but not
transients, if in fact that's what happening, some more work has to be
done. A good explanation doesn't mix the various possibilities together;
it separates them out. Nelson Pass says, "
The Mosfet designs on the market are also Class AB designs. The transfer
curve of Mosfets reveals serious nonlinearities at low bias

**Which is exactly what I said further down the thread. The 'knee' of
MOSFETs is much higher than that of BJTs, yet MOSFETs are rarely operated
with significantly more bias current than BJTs. A critical failure IMO.


currents, resulting in crossover nonlinearity in push-pull designs. This
design flaw makes for a sonic signature that many have referred to as

"Mosfet mist", where a loss of detail is apparent."

His explanation is different from yours; it is unlikely that both
explanations would contribute in approximately equal proportions. And he
isn't necessarily right. Here's my own personal anecdote.

**Perhaps, but I happen to think he is on the money. MOSFETs operating at
elevated bias currents DO sound pretty decent. They do not have the
compression effects I note with low bias designs. They also sound notably
cleaner and more articulate. As good, in fact, as a decent BJT deisgn
operating at significantly lower bias currents.


The Hafler XL-280 is an improved version of the DH-200/220, but it looks
very similar. It has six output devices/channel; the bias current is the
same 100ma/device, it has JFET inputs, but it looks pretty much the
same -- except that there is a small air plate varicap in the output.
This is/was to be used with a comparator bridge lent by the dealer to
null the difference between the amp input and output. I've played with
it, although recently, I've left it untouched. The amp is flat far above
the audible range, with a slewing rate of 75 v/us, but it is said to
have a peak at 170 kHz, adjusted by the cap. This amplifier does not
have the liquid mist of a DH-200; at least one review, perhaps Audio,
stated that it had the greatest amount of low level detail of any amp
they had heard. Nevertheless, the amplifier does sound a little flat, or
undynamic.

**Of course. It is a low bias, conventional MOSFET amp. They're all very
similar in my experience.


But when the amps are bridged, the sound changes completely. I use a
pair with the NEAR 50m's. In bridged mode, they sound like a very, very
good amplifier. What happens when an amplifier is bridged? Does the
damping factor halve?

**Yep. Along with a bunch of other problems and advantages. Personally, I
have serious issues with most bridged amps. Mainly because, at clipping,
the results are extremely unpridictable. Damping factors SEEMS to drop to
zero in many amps. Perhaps it is the fact that the amps can never be
absolutely perfectly matched and problems arise due to that. I'm not
certain, but bridging amps seems to improve the dynamic abilities, but it
also seems to introduce other problems which may be worse to many
listeners.

The XL-280 has a larger cousin, the XL-600, with a similar
circuit, the same air varicap, and 8 devices/channel, run at
100ma/device. It has a damping factor of 80, approximately half that of
the XL-280. The XL-600 has enjoyed considerable popularity in U.S.
studios, as a very good all-around amp. It sounds indistingushable from
the bridged XL-280's. I have both in my rack, but I use the 280's in the
winter, because they have no fan.

I wen through the above to show that the MOSFET mist, which still
afflicts certain modern designs, such as the ADCOM pieces, can
apparently be diminished or eliminated to the point where the result is
considered highly desirable, at least by some ears, while still
maintaining the traditional zero-voltage gain output stage.


The distorted
sine wave would be decomposable into a Fourier series with higher
powers. The extreme of this form of compression results in something
approximating a square wave. Please explain how an amplifier can
compress while having excellent harmonic distortion.

**Er, because it can.

Did I see your hands wave? Please say that again with your hands in your
pockets

**Sorry. I couldn't resist.



Because of gate capacitance and on resistance, MOSFETS do compress,

**Their compression, I believe is more to do with the negative Tempco
of Gm.

but in
order to meet rated distortion at rated power, they do this at power
levels above the rated power. This is not an egregious flaw; the amp
lacks headroom in a manner similar to Class A amplifiers. But the
classic MOSFET design also provides a benefit similar to pure Class A
bipolar amps; extremely low distortion at low power.

**Only because it uses massive amounts of Global NFB. Due to the high
levels of distortion at low currents, MOSFETs need to be biased on real
hard, or be used with huge amounts of NFB (usually Global). Except for
very high bias designs, there are no (to the best of my knowledge) Zero
Global NFB MOSFET amps.


The result is an ideal
clipping characteristic.

**Sort of.

I'll admit it has a characteristic sound, but imho,
you come down hard on what some of us consider a very useful
characteristic. I can drive one of the classic Hafler amps with a
source that has a very high peak-to-crest ratio, such as certain
piano music. At high volumes, any other amp exhibits some audible
clipping.

**Nope. Haflers are no different to many other amps, WRT clipping.
Clip them hard and they sound harsh and nasty. Possibly less so than
many amps, but nasty, nevertheless. BTW: There are many other schemes
which exist to keep an amp (BJT) from exhibint unpleasant clipping
characteristics. Most involve sacrificing a few Volts of headroom.
NAD is one such promoter of "soft clipping" type systems. There are
others. They cost a little more, but can provide demonstable
benefits. The best systems keep the anti-clipping system outside the
feedback loop.

The Hafler, never.

I have a NAD PE receiver, and my perception is that it does not clip
as cleanly as a Hafler.

**Which model?

7225PE

**AHA! Note the PE moniker. They are sonic disasters. All of them. The
clipping characteristic can be utterly appalling in the PE designs. Try
it sometime (not connected to speakers!). Connect to a dummy load, hang a
'scope off the end and crank the volume up to clipping. When the high
Voltage power supply shuts off, the amp falls into VERY severe clipping
and the resultant sound is terrible, as is the potential for speaker
damage.


ALL of the PE NADs are utter horrors. They clip badly. Soft
clipping notwithstanding. In any case, I used the NAD as an exmaple.
The NAD scheme is primitive and not all that good, but it does work.
NADs clip more gracefully than most of their competition.

When driving Acoustat panels with a DH-200 or XL-280, a
deliberate twist of the volume knob full clockwise (which the
Acoustats can tolerate, they're rated at 117db), produces no audible
clipping. The amplifier has to clip, but does not manifest a typical
clipping signature. In mentioning Hafler, I specifically mean only
those based on the original Hafler design: the DH and XL models. When
Rockford bought Hafler, and then Acoustat, they eventually replaced
the original Hafler design completely with the Transnova circuitry. As
much as I like them, these amplifiers do clip audibly, because they do
drive the MOSFETs straight to the rails.

**They use a higher Voltage rail for the drivers?

The rail voltage in the Transnova is 72V. However, because the outputs
have voltage gain, the drivers are operated from a regulated 25V rail.

**Interesting. Do you mean that the drivers are operated from a supply
which is operating 25 Volts ABOVE the 72 Volts?

No, actually 25V referenced to zero. Since the outputs have voltage gain,
they do not have to be driven at full voltage like conventional voltage
followers.

**K.


--
Trevor Wilson
www.rageaudio.com.au
Trevor, you definitely have a point to consider.. Like everything else in
this underfunded business, there is no economic motivation to really nail
it down, like stress factors in a wide-body jet. Since I have two bridged
MOSFET amps, and an XL-600, both with conventional voltage-follower
circuitry, that don't have the characteristic MOSFET mist, I'm not
convinced, nor do I dismiss your theory. Could the Excelinear circuit be a
cheap trick that fools the ear into thinking there is no "mist" present?
Perhaps.

And the ADCOM HEXFET amps, designed by John Curl, who we have just
referenced, have a horrible case of "mist". Bad amps. Waste of iron and
silicon.

**I've never seen any Adcom MOSFET amps, but I've seen a few BJT ones.
Whilst they have some good ideas, they appear to be crippled by cost
cutting.


BTW, the original Transnova circuit, as implemented in the Acoustat, has
only three stages. The first two are JFETs. The reduction in number of
stages, and the speed of the devices permits an increase in the amount of
feedback. These amplifiers have remarkable clarity, even though the output
coupling is almost bizarre, and massive feedback (which Strickland claims
also incorporates positive, or complementary) may be the thing which
overcomes whatever it is in MOSFETs that has to be overcome.

**Cool.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
news
SNIP

**It's OK. Most do, when I present them with that information.
However, it is the ONLY explanation which makes sense of the
"softness" associated with Haflers, Perreaux and other early, standard
MOSFET amps. Even with the level WAY below clipping, even a crappy BJT
amp (like a late model Phase Linear) the lack of dynamics in the
MOSFET amps is immediately noticable. You, yourself, have acknowledged
in your statement that they are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine
wave.

**Except that I am not talking about sine waves. I am talking about
fast rise time, assymetrical transients. Just likke the stuff we get
in music. The Hafler does a fine job of reproducing sine waves, just
like any other MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I
would need to see a gapless explanation.

**OK. I'll try to explain later. Briefly, however, consider the effects,
at chip level, when a MOSFET is subject to the heating via a fast rising
transient (which causes lots of current to flow). The MOSFET very
briefly tends to reduce this current, via the negative tempco of Gm. The
NFB loop will tend to counteract this effect to some degree, but, IMO,
not all that successfully. Very high bias designs (ala Pass, et al) get
around this problem by operating the chip at constant high temps. Thus,
the effect is not noticable. Low bias MOSFET amps do suffer with this
compression effect. Sound reasonable?

Not proven, but definitely reasonable, ie., within consideration. But if
we listen to Francois, low-biased MOSFETs may be in the negative
temperature coefficient region.

**Absolutely, which is why for MOSFETs to sound reasonable, they MUST be
biased on hard. Very hard. At least ten times harder than a BJT. And then,
all you get is a linearity which is approximately similar to a BJT.

Trevor, one of us has a sign reversed. According to the stuff Francois
brought forth, a MOSFET has a negative temperature coefficient if the
gate-to-drain voltage is below a certain level, ie., which would tend to
imply that if the bias is below a certain level, a negative temperature
coefficient exists. Above some level, be it bias or signal, a positive
coefficient exists. See http://www.irf.com/technical-info/guide/device.html,
where the coefficient refers to the voltage drop. This means to me that for
bias below a certain level, the thermal effect would tend to do the reverse
of compression; the error would tend to magnify transients. For bias above a
certain level, the temperature coefficient goes positive, which means that
the thermal effect, if it is significant, does indeed compress the signal.

So compression may occur due to thermal effects, but it seems to me from the
above that one cannot draw the conclusion that high bias = good, low bias =
bad. In general, bias works by the equivalent of Taylor expansion around a
nonlinear function; the expansion is locally linear around the point
established by the bias current. The size of the linear region around the
expansion point is a neighborhood that is small in comparison to the local
rate of change of the function. High bias makes the expansion locally linear
because the scale factor of the expansion is determined by the bias current.

Physically, the reasoning is like this: High bias makes the junction hot,
and the hot junction loses heat proportional to the temperature differential
divided by the thermal resistance. The hotter the bias current makes the
junction, the less significant the variable heating caused by the signal.

The above is in support of your opinion, but with somewhat different
reasoning. At the same time, I maintain that there are enough successful
MOSFET designs out there to indicate that even if the linearity is nonlinear
in nature, feedback can make it work.

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
news
SNIP

**It's OK. Most do, when I present them with that information.
However, it is the ONLY explanation which makes sense of the
"softness" associated with Haflers, Perreaux and other early,
standard MOSFET amps. Even with the level WAY below clipping, even a
crappy BJT amp (like a late model Phase Linear) the lack of dynamics
in the MOSFET amps is immediately noticable. You, yourself, have
acknowledged in your statement that they are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine
wave.

**Except that I am not talking about sine waves. I am talking about
fast rise time, assymetrical transients. Just likke the stuff we get
in music. The Hafler does a fine job of reproducing sine waves, just
like any other MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I
would need to see a gapless explanation.

**OK. I'll try to explain later. Briefly, however, consider the
effects, at chip level, when a MOSFET is subject to the heating via a
fast rising transient (which causes lots of current to flow). The
MOSFET very briefly tends to reduce this current, via the negative
tempco of Gm. The NFB loop will tend to counteract this effect to some
degree, but, IMO, not all that successfully. Very high bias designs
(ala Pass, et al) get around this problem by operating the chip at
constant high temps. Thus, the effect is not noticable. Low bias MOSFET
amps do suffer with this compression effect. Sound reasonable?

Not proven, but definitely reasonable, ie., within consideration. But if
we listen to Francois, low-biased MOSFETs may be in the negative
temperature coefficient region.

**Absolutely, which is why for MOSFETs to sound reasonable, they MUST be
biased on hard. Very hard. At least ten times harder than a BJT. And
then, all you get is a linearity which is approximately similar to a BJT.

Trevor, one of us has a sign reversed. According to the stuff Francois
brought forth, a MOSFET has a negative temperature coefficient if the
gate-to-drain voltage is below a certain level, ie., which would tend to
imply that if the bias is below a certain level, a negative temperature
coefficient exists. Above some level, be it bias or signal, a positive
coefficient exists. See
http://www.irf.com/technical-info/guide/device.html, where the coefficient
refers to the voltage drop. This means to me that for bias below a
certain level, the thermal effect would tend to do the reverse of
compression; the error would tend to magnify transients. For bias above a
certain level, the temperature coefficient goes positive, which means that
the thermal effect, if it is significant, does indeed compress the signal.

**I assumed we were discussing the Hitachi MOSFETs. They suffer the negative
tempco of Gm more severely than the IRF devices.


So compression may occur due to thermal effects, but it seems to me from
the above that one cannot draw the conclusion that high bias = good, low
bias = bad. In general, bias works by the equivalent of Taylor expansion
around a nonlinear function; the expansion is locally linear around the
point established by the bias current. The size of the linear region
around the expansion point is a neighborhood that is small in comparison
to the local rate of change of the function. High bias makes the expansion
locally linear because the scale factor of the expansion is determined by
the bias current.

Physically, the reasoning is like this: High bias makes the junction hot,
and the hot junction loses heat proportional to the temperature
differential divided by the thermal resistance. The hotter the bias
current makes the junction, the less significant the variable heating
caused by the signal.

**I would agree with that.


The above is in support of your opinion, but with somewhat different
reasoning. At the same time, I maintain that there are enough successful
MOSFET designs out there to indicate that even if the linearity is
nonlinear in nature, feedback can make it work.

**Really? Name one, really good, low bias MOSFET amp. Not a second rate amp,
but a really good one. One which has received universally excellent praise.
The only MOSFET amps I know which have garnered really good reception are
high bias models.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

"Robert Morein" wrote in message
news
SNIP

**It's OK. Most do, when I present them with that information.
However, it is the ONLY explanation which makes sense of the
"softness" associated with Haflers, Perreaux and other early,
standard MOSFET amps. Even with the level WAY below clipping, even a
crappy BJT amp (like a late model Phase Linear) the lack of dynamics
in the MOSFET amps is immediately noticable. You, yourself, have
acknowledged in your statement that they are "soft" sounding.

Even the DH-200 was specced
at something like 0.2% distortion at full power. If the amplifier
compressed a full power sine wave, the result would not be a sine
wave.

**Except that I am not talking about sine waves. I am talking about
fast rise time, assymetrical transients. Just likke the stuff we get
in music. The Hafler does a fine job of reproducing sine waves, just
like any other MOSFET amp. It's music that it stuggles with.

I appreciate your effort to explain the characteristic sound, but I
would need to see a gapless explanation.

**OK. I'll try to explain later. Briefly, however, consider the
effects, at chip level, when a MOSFET is subject to the heating via a
fast rising transient (which causes lots of current to flow). The
MOSFET very briefly tends to reduce this current, via the negative
tempco of Gm. The NFB loop will tend to counteract this effect to some
degree, but, IMO, not all that successfully. Very high bias designs
(ala Pass, et al) get around this problem by operating the chip at
constant high temps. Thus, the effect is not noticable. Low bias
MOSFET amps do suffer with this compression effect. Sound reasonable?

Not proven, but definitely reasonable, ie., within consideration. But
if we listen to Francois, low-biased MOSFETs may be in the negative
temperature coefficient region.

**Absolutely, which is why for MOSFETs to sound reasonable, they MUST be
biased on hard. Very hard. At least ten times harder than a BJT. And
then, all you get is a linearity which is approximately similar to a
BJT.

Trevor, one of us has a sign reversed. According to the stuff Francois
brought forth, a MOSFET has a negative temperature coefficient if the
gate-to-drain voltage is below a certain level, ie., which would tend to
imply that if the bias is below a certain level, a negative temperature
coefficient exists. Above some level, be it bias or signal, a positive
coefficient exists. See
http://www.irf.com/technical-info/guide/device.html, where the
coefficient refers to the voltage drop. This means to me that for bias
below a certain level, the thermal effect would tend to do the reverse of
compression; the error would tend to magnify transients. For bias above a
certain level, the temperature coefficient goes positive, which means
that the thermal effect, if it is significant, does indeed compress the
signal.

**I assumed we were discussing the Hitachi MOSFETs. They suffer the
negative tempco of Gm more severely than the IRF devices.

I didn't know there was a difference, but I'll look.


So compression may occur due to thermal effects, but it seems to me from
the above that one cannot draw the conclusion that high bias = good, low
bias = bad. In general, bias works by the equivalent of Taylor expansion
around a nonlinear function; the expansion is locally linear around the
point established by the bias current. The size of the linear region
around the expansion point is a neighborhood that is small in comparison
to the local rate of change of the function. High bias makes the
expansion locally linear because the scale factor of the expansion is
determined by the bias current.

Physically, the reasoning is like this: High bias makes the junction
hot, and the hot junction loses heat proportional to the temperature
differential divided by the thermal resistance. The hotter the bias
current makes the junction, the less significant the variable heating
caused by the signal.

**I would agree with that.


The above is in support of your opinion, but with somewhat different
reasoning. At the same time, I maintain that there are enough successful
MOSFET designs out there to indicate that even if the linearity is
nonlinear in nature, feedback can make it work.

**Really? Name one, really good, low bias MOSFET amp. Not a second rate
amp, but a really good one. One which has received universally excellent
praise. The only MOSFET amps I know which have garnered really good
reception are high bias models.

I've never heard a low bias bipolar amp that sounded excellent to me.
Therefore, there are none that received universally excellent praise But
seriously, there is too much individual preference to make the question
valid. At best, an amplifier can have a following. Take a look at this page:
http://audioreview.com/mfr/hafler/am...6_1583CRX.ASPX Notice how
many users find qualities in these amplifiers, even the traditional "DH-"
designs, that apparently outweigh your sensitivity to their particular
artifacts. Pay particular attention to the DH-500. Considering how
obnoxiously noisy the fan of a DH-500 is, the sound must have quite an
allure to those devoted to it. That's how I feel about my XL-600(s), anyway.

"Trevor Wilson" wrote in
message

**Nope. Haflers are no different to many other amps, WRT
clipping.

Agreed.

Clip them hard and they sound harsh and nasty.

That's because they put nice flat tops on the waves when they clip them.

The idea that choice of active device type modifies clipping characteristics
is yet another audio myth. Your typical good tubed amp, produces
nicely-flat-topped waves. Your typical good BJT amp, produces similar
nicely-flat-topped waves. Your typical good FET amp, produces similar
nicely-flat-topped waves.

The flat-topping comes from the power amp's circuit design - it's a
consequence of low distortion below clipping, negative feedback, good
bandwidth and good stability.

"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote in
message

**Nope. Haflers are no different to many other amps, WRT
clipping.

Agreed.

Clip them hard and they sound harsh and nasty.

That's because they put nice flat tops on the waves when they clip them.

The idea that choice of active device type modifies clipping
characteristics is yet another audio myth. Your typical good tubed amp,
produces nicely-flat-topped waves. Your typical good BJT amp, produces
similar nicely-flat-topped waves. Your typical good FET amp, produces
similar nicely-flat-topped waves.

The flat-topping comes from the power amp's circuit design - it's a
consequence of low distortion below clipping, negative feedback, good
bandwidth and good stability.

This is contradicted by personal experience.

"Robert Morein" wrote in message

"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote
in message

**Nope. Haflers are no different to many other amps, WRT
clipping.

Agreed.

Clip them hard and they sound harsh and nasty.

That's because they put nice flat tops on the waves when
they clip them. The idea that choice of active device type modifies
clipping characteristics is yet another audio myth. Your
typical good tubed amp, produces nicely-flat-topped
waves. Your typical good BJT amp, produces similar
nicely-flat-topped waves. Your typical good FET amp, produces similar
nicely-flat-topped waves. The flat-topping comes from the power amp's
circuit
design - it's a consequence of low distortion below
clipping, negative feedback, good bandwidth and good
stability.

This is contradicted by personal experience.

The laws of physics dictate how amps clip. We can therefore conclude that
the laws of physics work different in or around Philadelphia.

"Arny Krueger" wrote in message
. ..
"Robert Morein" wrote in message

"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote
in message

**Nope. Haflers are no different to many other amps, WRT
clipping.

Agreed.

Clip them hard and they sound harsh and nasty.

That's because they put nice flat tops on the waves when
they clip them. The idea that choice of active device type modifies
clipping characteristics is yet another audio myth. Your
typical good tubed amp, produces nicely-flat-topped
waves. Your typical good BJT amp, produces similar
nicely-flat-topped waves. Your typical good FET amp, produces similar
nicely-flat-topped waves. The flat-topping comes from the power amp's
circuit
design - it's a consequence of low distortion below
clipping, negative feedback, good bandwidth and good
stability.

This is contradicted by personal experience.

The laws of physics dictate how amps clip. We can therefore conclude that
the laws of physics work different in or around Philadelphia.

Of course. Ever hear of the "Philadelphia Experiment" ?

wrote:
I just bought a clean Macintosh MA 6100 integrated amp at a bricks and
motar auction. I haven't done anything with the 6100 other than
plugging it in (all the lights work and it didn't blow a breaker) and
it will be a few days before I can put it in my system and make an
evaluation. I currently have a Hafler 220 amp and Hafler 110 preamp. I
know that the Mac was built to the highest standards of the mid 70s,
but even my Hafler, a modest piece of equipment, has poly caps, metal
resistors, better pots etc. If I like the way the Mac sounds, would it
be worthwhile or even desirable to upgrade individual components? My
system is two channel, music only and I listen to FM, CDs and records.

After giving the McIntosh a listen, I've decided to keep my Hafler amp
and preamp. The McIntosh is cool looking and the preamp controls are
more flexible than the Hafler's, but I didn't hear a significant
improvement to my system sound. After reinstalling the Haflers I did
hear the Mosfet Mist that people are always talking about. I think the
Haflers have more POOGEing potential and any mods I eventually make to
them will not affect their modest cash value. The rational economic
decision is to auction the McIntosh "you-know-where". The auction has 5
days to go as of the date of this post. Do a search and you'll find it.