"Robert Morein" wrote in message
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"Trevor Wilson" wrote in message
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"Robert Morein" wrote in message
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"Trevor Wilson" wrote in message
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"Robert Morein" wrote in message
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"Trevor Wilson" wrote in message
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"Robert Morein" wrote in message
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"Trevor Wilson" wrote in message
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"Trevor Wilson" wrote in
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"Robert Morein" wrote in message
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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