[Eeyore]

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?

Graham

[Geoff]

Eeyore wrote:
Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?

Hotter ?

I can't remember the models - it was a while ago. Only audible difference
to me was that the AB one sounded harsher when louder. But the Class A
ampcouldn't actually get that loud anyway, so not fair comparison I guess.

geoff

[Eeyore]

Geoff wrote:

Eeyore wrote:
Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?

Hotter ?

I can't remember the models - it was a while ago. Only audible difference
to me was that the AB one sounded harsher when louder.

Not too surprising.

But the Class A
ampcouldn't actually get that loud anyway, so not fair comparison I guess.

Did you notice any differences at lower levels ?

Graham

[Sander deWaal]

Eeyore said:


Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?


I have extensive listening (and building) experience with hybrid amps,
a tube driving (one or more) complementary pairs of MOSFETs biased in
A.

Because they're my own designs, I don't know how to compare them to
commercial amps, since it's been a long time since I listened
extensively to a commercial amplifier at home.

From recent demos I did with them, the most comments I heard were
"effortless sound, somewhat restricted, but detailed and powerful when
necessary".
Also, the terms "forgiving" and "smooth" were uttered.
Some people preferred them above a pair of modified Hypex UcD400AD,
though. And of course, others did not.

I guess that means they do color the sound a bit.
In fact I know they do, I *intended* them to sound like that ;-)

I still think my KT88 monsters that came ready recently, beat them
wrt. placing and detail, but they're rather sensitive to the kind of
speaker attached, and do deliver less power because they're wired in
triode.
The hybrids are more "forgiving", they easily drive 2 Maggies in
parallel per channel.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Bertie the Bunyip]

Eeyore wrote in
:

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?

Graham


netkkkopin gfjukkkkwit




bertie

[Bertie the Bunyip]

Eeyore wrote in
:



Geoff wrote:

Eeyore wrote:
Have you ever spent any time listening to a true Class A solid
state amplifiers ?

Any comments on how it sounded compared to any other types ?

Hotter ?

I can't remember the models - it was a while ago. Only audible
difference to me was that the AB one sounded harsher when louder.

Not too surprising.

But the Class A
ampcouldn't actually get that loud anyway, so not fair comparison I
guess.

Did you notice any differences at lower levels ?


Wannnabe luser boi


bdertie

[Frank Stearns]

Eeyore writes:

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?

5-6 years ago I went through a rather extensive amp eval period, trying
serveral different solid state and tube amps, the most expensive being a
$6K Levinson and the cheapest a $400 Parasound. Power outputs ranged from
20 wpc to 200. Load was a pair of soffit-mounted Tannoy SGM10Bs with
Mastering Lab crossovers. The room is treated, and has few problems
and reveals much.

Most of the amps sounded pretty good. The tube amp, a Bel, I believe, had
some nice qualities in the mid range but was otherwise dull or muffled
sounding. All were AB, with one exception.

The winner was the 30 wpc class-A Pass Labs Aleph 3 -- not because it was
"oooh" this and "ahhh" that, it simply was the least colored. Once you
"heard" its transparancy, it was the other amps that started to sound
colored.

Its failing, however, had to do (apparently) with less than ideal LF
damping and/or lower power. This, as well as some LF IM problems attached
to the Tannoys, disappeared once I added subs and biamped (had to mod the
active xover -- good design, crappy parts), crossing over just above the
Tannoy port frequency at 60 Hz. (This is a hybrid 3-way system -- active
LF xover, but passive for the mid and top.)

It's a hell of a system for the money, and nice to mix on.

Class A has it merits if you can get into it for a reasonable price and
know some of the negatives (such as heat and weight).

Frank Stearns
Mobile Audio


--

[Sander deWaal]

Frank Stearns said:


Class A has it merits if you can get into it for a reasonable price and
know some of the negatives (such as heat and weight).



Just as with tubes, I think class A is best suited to the DIY-ers who
know what they are doing.

Oh, that would rule me out. Sorry folks ;-)

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Dave Plowman (News)]

In article ,
Eeyore wrote:
Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Yes. A mate drove his ESLs with a Sugden. One of the cleanest sounding
systems I've ever heard. Wouldn't shake the windows, though. ;-)

--
*Hard work has a future payoff. Laziness pays off NOW.

Dave Plowman London SW
To e-mail, change noise into sound.

[Trevor Wilson]

"Eeyore" wrote in message
...
Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few tens of
milliwatts. Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud. For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference. Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high for
regular US outlets, without losing mains Voltage. At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'. Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to design
an amplifier properly. Once bias current is set above the 'knee' of the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more Class A bias
is superfluous.

Think of it this way: A badly designed Class A/B amplifier will probably
sound better when operating in Class A. A well designed Class A/B amplifier
will probably sound slightly worse when operating in Class A.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[William Sommerwerck]

I used to own Krells. My gut reaction (totally unsubtantiated by any sort of
comparative listening tests) was that they had a "tight", "controlled",
effortless sound.

[William Sommerwerck]

We all have. Pretty much every amplifier operates class A to
a few tens of milliwatts. Plenty loud enough for quiet listening.
Some high bias class AB designs operate to a couple of watts
in class A.

The Parasound A21, for example, is class A up to 8 watts (not Watts) per
channel into an 8-ohm load. That's fairly loud, unless you have rather
insensitive speakers.

[Trevor Wilson]

"Dave Plowman (News)" wrote in message
...
In article ,
Eeyore wrote:
Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Yes. A mate drove his ESLs with a Sugden. One of the cleanest sounding
systems I've ever heard. Wouldn't shake the windows, though. ;-)

**Sugdens have never built pure Class A amps (whatever that means). They
have only ever built high bias Class A/B designs. And, of course, Class A is
only Class A when specified into a particular load impedance. Usually 8
Ohms. Given the fact that ESLs vary all over the map, impedance-wise,
suggesting that the amp is Class A is even less likely.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Bertie the Bunyip]

"Bret Ludwig" wrote in
ups.com:


William Sommerwerck wrote:
I used to own Krells. My gut reaction (totally unsubtantiated by any
sort of comparative listening tests) was that they had a "tight",
"controlled", effortless sound.


Really, if you build a tube amp that sounds like a Krell, you have a
pretty good amplifier.

I detest Krell's attitude, think their prices are ridiculous, and the
weight and heat and power consumption are ridiculous. But the sound is
without flaw, really

[Bertie the Bunyip]

"Bret Ludwig" wrote in
oups.com:


Trevor Wilson wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
Eeyore wrote:
Have you ever spent any time listening to a true Class A solid
state amplifiers ?

Yes. A mate drove his ESLs with a Sugden. One of the cleanest
sounding systems I've ever heard. Wouldn't shake the windows,
though. ;-)

**Sugdens have never built pure Class A amps (whatever that means).
They have only ever built high bias Class A/B designs. And, of
course, Class A is only Class A when specified into a particular load
impedance. Usually 8 Ohms. Given the fact that ESLs vary all over the
map, impedance-wise, suggesting that the amp is Class A is even less
likely.

This is actually true.

High bias AB amps operate in class A through most of the power range
they spend all their time in, giving the advantage of Calss A
operation where it is needed, and rather than running out of power
when this is exceeded they simply transition into Class B.

So-called experts, and their toadies and asskissers (such as
Jeboo-selling Randy Slone) have pounded on the idea that Class AB is a
poor design methodology because of "transconductance doubling".
Obviously this is nonexistant in the region of Class A operation

[Scott Dorsey]

Bret Ludwig wrote:
High bias AB amps operate in class A through most of the power range
they spend all their time in, giving the advantage of Calss A operation
where it is needed, and rather than running out of power when this is
exceeded they simply transition into Class B.

This is true. The problem, however, is that although the distortion may
be much lower in class AB than in class B, the distortion spectrum is often
less pleasant, at least to my ear. I often find a given output stage sounds
better biased into class B than up higher into class AB.

For low power studio-grade applications, though, there's no reason not to
just go whole-hog and run everything Class A. Electricity is cheap.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Trevor Wilson]

"Scott Dorsey" wrote in message
...
Bret Ludwig wrote:
High bias AB amps operate in class A through most of the power range
they spend all their time in, giving the advantage of Calss A operation
where it is needed, and rather than running out of power when this is
exceeded they simply transition into Class B.

This is true. The problem, however, is that although the distortion may
be much lower in class AB than in class B, the distortion spectrum is
often
less pleasant, at least to my ear. I often find a given output stage
sounds
better biased into class B than up higher into class AB.

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my words:
"Otherwise identical".


For low power studio-grade applications, though, there's no reason not to
just go whole-hog and run everything Class A. Electricity is cheap.

**There are plenty of reasons NOT to go pure Class A and very few to do so.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Eeyore]

Trevor Wilson wrote:

"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few tens of
milliwatts.

That's not what I meant by true Class A though.


Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the crossover
region the output device transconductance is varying widely and putting
non-linearity into the transfer characteristic


For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has less overall
effect as a percentage of signal level. It doesn't totally go away though.


Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high for
regular US outlets, without losing mains Voltage.

Really ?


At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.


Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to design
an amplifier properly. Once bias current is set above the 'knee' of the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more Class A bias
is superfluous.

There are still some advantages in not turning the devices hard off though.


Think of it this way: A badly designed Class A/B amplifier will probably
sound better when operating in Class A. A well designed Class A/B amplifier
will probably sound slightly worse when operating in Class A.

I can't understand the rationale for your 2nd idea there.

Graham

[Mike Rivers]

Eeyore wrote:
Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?

Amplifiers are amplifiers. Some sound better than others. There's
nothing magic about a Class A amplifier, but it sure sounds good on the
marketing literature. Most people have the good sense to not use a
Class C amplifier for high quality audio.

[Trevor Wilson]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few tens
of
milliwatts.

That's not what I meant by true Class A though.

**'True Class A' is a very rubbery definition. A 'True Class A' amplifier
rated at (say) 50 Watts @ 8 Ohms, will only be 25 Watts Class A, when
driving 4 Ohms, 12.5 Watts @ 2 Ohms, and so on. Given the fact that a
typical 8 Ohms speaker can easily exhibit impedance minima down to 3 Ohms,
you'll see the problem.



Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the
crossover
region the output device transconductance is varying widely and putting
non-linearity into the transfer characteristic

**Well, you've managed to narrow your choice of devices down, significantly,
since the amplification factor of BJTs is expressed as hFE. Current gain.
The variation in current gain of modern BJTs is spectacularly low, over very
wide Collector currents. You need to examine the curves on this page:

http://www.futurlec.com/Transistors/2SC5200.shtml

Pay close attention to the hFE/Ic curves. You'll note that the device is
linear from 10ma all the way through to 3 Amps.




For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has less
overall
effect as a percentage of signal level. It doesn't totally go away though.

**More bull****. If one goes to the trouble to match output devices, then,
combined with the excellent linearity I previously mentioned, crossover
distortion does not exist. It will be swamped by other forms of distortion
and noise.



Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high for
regular US outlets, without losing mains Voltage.

Really ?

**Yes, really. US 117VAC receptacles are rated for 1,500 Watts. In reality,
I have measured significant Voltage drops with as little as 1,000 Watt
loads. IMO, it is for this reasona that manufacturers such as Krell stopped
building Class A amplifiers for domestic consumption.



At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.

**After you try it, get back to me. US 117VAC power receptacles and
associated wiring is pretty ordinary, compared to almost anywhere else on
the planet.



Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to
design
an amplifier properly. Once bias current is set above the 'knee' of the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more Class A
bias
is superfluous.

There are still some advantages in not turning the devices hard off
though.

**No. However, you can name those alleged advantages, if you wish.



Think of it this way: A badly designed Class A/B amplifier will probably
sound better when operating in Class A. A well designed Class A/B
amplifier
will probably sound slightly worse when operating in Class A.

I can't understand the rationale for your 2nd idea there.

**Douglas Self explains it very nicely.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Eeyore]

Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few tens
of milliwatts.

That's not what I meant by true Class A though.

**'True Class A' is a very rubbery definition. A 'True Class A' amplifier
rated at (say) 50 Watts @ 8 Ohms, will only be 25 Watts Class A, when
driving 4 Ohms, 12.5 Watts @ 2 Ohms, and so on. Given the fact that a
typical 8 Ohms speaker can easily exhibit impedance minima down to 3 Ohms,
you'll see the problem.

My understanding of the textbook definition is that the device(s) are always
conducting for the entire cycle i.e. never switch off at all output power
levels.


Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the
crossover
region the output device transconductance is varying widely and putting
non-linearity into the transfer characteristic

**Well, you've managed to narrow your choice of devices down, significantly,
since the amplification factor of BJTs is expressed as hFE. Current gain.
The variation in current gain of modern BJTs is spectacularly low, over very
wide Collector currents. You need to examine the curves on this page:

http://www.futurlec.com/Transistors/2SC5200.shtml

Pay close attention to the hFE/Ic curves. You'll note that the device is
linear from 10ma all the way through to 3 Amps.

Current gain doesn't much bother me. It'll be coming from a very low impedance
stage.


For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has less
overall effect as a percentage of signal level. It doesn't totally go away
though.

**More bull****. If one goes to the trouble to match output devices, then,
combined with the excellent linearity I previously mentioned, crossover
distortion does not exist. It will be swamped by other forms of distortion
and noise.

You can do all this without matched devices. I simply can't conceive that the
change in gm won't ever have an effect.


Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high for
regular US outlets, without losing mains Voltage.

Really ?

**Yes, really. US 117VAC receptacles are rated for 1,500 Watts. In reality,
I have measured significant Voltage drops with as little as 1,000 Watt
loads. IMO, it is for this reasona that manufacturers such as Krell stopped
building Class A amplifiers for domestic consumption.

At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.

**After you try it, get back to me. US 117VAC power receptacles and
associated wiring is pretty ordinary, compared to almost anywhere else on
the planet.

How would ac power voltage sag cause a compressed sound ?


Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to
design an amplifier properly. Once bias current is set above the 'knee' of
the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more
Class A bias is superfluous.

There are still some advantages in not turning the devices hard off
though.

**No. However, you can name those alleged advantages, if you wish.

Elimination of switching effects.


Think of it this way: A badly designed Class A/B amplifier will probably
sound better when operating in Class A. A well designed Class A/B
amplifier will probably sound slightly worse when operating in Class A.

I can't understand the rationale for your 2nd idea there.

**Douglas Self explains it very nicely.

Call me a sceptic then !


Graham

[Trevor Wilson]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few
tens
of milliwatts.

That's not what I meant by true Class A though.

**'True Class A' is a very rubbery definition. A 'True Class A' amplifier
rated at (say) 50 Watts @ 8 Ohms, will only be 25 Watts Class A, when
driving 4 Ohms, 12.5 Watts @ 2 Ohms, and so on. Given the fact that a
typical 8 Ohms speaker can easily exhibit impedance minima down to 3
Ohms,
you'll see the problem.

My understanding of the textbook definition is that the device(s) are
always
conducting for the entire cycle i.e. never switch off at all output power
levels.

**And, unless the precise load is specified, then the definition of Class A
is meaningless.



Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the
crossover
region the output device transconductance is varying widely and putting
non-linearity into the transfer characteristic

**Well, you've managed to narrow your choice of devices down,
significantly,
since the amplification factor of BJTs is expressed as hFE. Current
gain.
The variation in current gain of modern BJTs is spectacularly low, over
very
wide Collector currents. You need to examine the curves on this page:

http://www.futurlec.com/Transistors/2SC5200.shtml

Pay close attention to the hFE/Ic curves. You'll note that the device is
linear from 10ma all the way through to 3 Amps.

Current gain doesn't much bother me. It'll be coming from a very low
impedance
stage.

**Current gain SHOULD bother you, since that is what we're discussing. The
linearity of the devices is exemplary, over a very wide current range and
down to quite low currents.



For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since
the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has less
overall effect as a percentage of signal level. It doesn't totally go
away
though.

**More bull****. If one goes to the trouble to match output devices,
then,
combined with the excellent linearity I previously mentioned, crossover
distortion does not exist. It will be swamped by other forms of
distortion
and noise.

You can do all this without matched devices.

**Using matched devices eliminates all possiblity of problems.

I simply can't conceive that the
change in gm won't ever have an effect.

**It probably would. However, I am suggesting that modern BJTs have such
excellent current linearity, that no problems will occur when using in Class
A/B.



Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high
for
regular US outlets, without losing mains Voltage.

Really ?

**Yes, really. US 117VAC receptacles are rated for 1,500 Watts. In
reality,
I have measured significant Voltage drops with as little as 1,000 Watt
loads. IMO, it is for this reasona that manufacturers such as Krell
stopped
building Class A amplifiers for domestic consumption.

At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.

**After you try it, get back to me. US 117VAC power receptacles and
associated wiring is pretty ordinary, compared to almost anywhere else on
the planet.

How would ac power voltage sag cause a compressed sound ?

**Think about it. Think about it in the context that few power amplifiers
use a regulated power supply.



Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to
design an amplifier properly. Once bias current is set above the
'knee' of
the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more
Class A bias is superfluous.

There are still some advantages in not turning the devices hard off
though.

**No. However, you can name those alleged advantages, if you wish.

Elimination of switching effects.

**Those effects can be elimintated through the use of matched linear
devices, constant operating temperatures and modest amounts of Class A bias
current. No full Class A operation is required.



Think of it this way: A badly designed Class A/B amplifier will
probably
sound better when operating in Class A. A well designed Class A/B
amplifier will probably sound slightly worse when operating in Class
A.

I can't understand the rationale for your 2nd idea there.

**Douglas Self explains it very nicely.

Call me a sceptic then !

**Read Self's work.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Scott Dorsey]

Trevor Wilson wrote:
"Scott Dorsey" wrote in message
...
Bret Ludwig wrote:
High bias AB amps operate in class A through most of the power range
they spend all their time in, giving the advantage of Calss A operation
where it is needed, and rather than running out of power when this is
exceeded they simply transition into Class B.

This is true. The problem, however, is that although the distortion may
be much lower in class AB than in class B, the distortion spectrum is
often
less pleasant, at least to my ear. I often find a given output stage
sounds
better biased into class B than up higher into class AB.

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my words:
"Otherwise identical".

That's not what I said. That is not at ALL what I said.

For low power studio-grade applications, though, there's no reason not to
just go whole-hog and run everything Class A. Electricity is cheap.

**There are plenty of reasons NOT to go pure Class A and very few to do so.

Other than size and heat?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Eeyore]

Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a few
tens of milliwatts.

That's not what I meant by true Class A though.

**'True Class A' is a very rubbery definition. A 'True Class A' amplifier
rated at (say) 50 Watts @ 8 Ohms, will only be 25 Watts Class A, when
driving 4 Ohms, 12.5 Watts @ 2 Ohms, and so on. Given the fact that a
typical 8 Ohms speaker can easily exhibit impedance minima down to 3
Ohms, you'll see the problem.

My understanding of the textbook definition is that the device(s) are
always conducting for the entire cycle i.e. never switch off at all output
power levels.

**And, unless the precise load is specified, then the definition of Class A
is meaningless.

It can be specified as a minimum load impedance.


Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the
crossover
region the output device transconductance is varying widely and putting
non-linearity into the transfer characteristic

**Well, you've managed to narrow your choice of devices down,
significantly,
since the amplification factor of BJTs is expressed as hFE. Current
gain.
The variation in current gain of modern BJTs is spectacularly low, over
very
wide Collector currents. You need to examine the curves on this page:

http://www.futurlec.com/Transistors/2SC5200.shtml

Pay close attention to the hFE/Ic curves. You'll note that the device is
linear from 10ma all the way through to 3 Amps.

Current gain doesn't much bother me. It'll be coming from a very low
impedance
stage.

**Current gain SHOULD bother you, since that is what we're discussing.

It's not what I'm discussing. I've had excellent results with 'super beta'
output stages. Commercial ( pro ) amplifiers simply can't used matched devices
for practical production and servicing reasons so you design the issue out.


The
linearity of the devices is exemplary, over a very wide current range and
down to quite low currents.

For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since
the
design eschews the use of Global NFB, it is far more sensitive to bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has less
overall effect as a percentage of signal level. It doesn't totally go
away though.

**More bull****. If one goes to the trouble to match output devices,
then,
combined with the excellent linearity I previously mentioned, crossover
distortion does not exist. It will be swamped by other forms of
distortion and noise.

You can do all this without matched devices.

**Using matched devices eliminates all possiblity of problems.

I don't want to used matched devices. In any case the gm still varies hugely at
small currents.


I simply can't conceive that the
change in gm won't ever have an effect.

**It probably would. However, I am suggesting that modern BJTs have such
excellent current linearity, that no problems will occur when using in Class
A/B.

That's not my experience. I should point out that I am targeting *ultra-low*
distortion figures.


Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high
for regular US outlets, without losing mains Voltage.

Really ?

**Yes, really. US 117VAC receptacles are rated for 1,500 Watts. In
reality,
I have measured significant Voltage drops with as little as 1,000 Watt
loads. IMO, it is for this reasona that manufacturers such as Krell
stopped building Class A amplifiers for domestic consumption.

At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.

**After you try it, get back to me. US 117VAC power receptacles and
associated wiring is pretty ordinary, compared to almost anywhere else on
the planet.

How would ac power voltage sag cause a compressed sound ?

**Think about it. Think about it in the context that few power amplifiers
use a regulated power supply.

It's a crappy design that's supply rail sensitive !


Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how to
design an amplifier properly. Once bias current is set above the
'knee' of the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more
Class A bias is superfluous.

There are still some advantages in not turning the devices hard off
though.

**No. However, you can name those alleged advantages, if you wish.

Elimination of switching effects.

**Those effects can be elimintated through the use of matched linear
devices, constant operating temperatures and modest amounts of Class A bias
current. No full Class A operation is required.

I'm talking about *switching effects* - carrier storage and stuff.


Think of it this way: A badly designed Class A/B amplifier will
probably
sound better when operating in Class A. A well designed Class A/B
amplifier will probably sound slightly worse when operating in Class
A.

I can't understand the rationale for your 2nd idea there.

**Douglas Self explains it very nicely.

Call me a sceptic then !

**Read Self's work.

I've browsed it occasionally I don't consider him to be especially any guru
though. In fact I've a sort of grudge to bear in fact.

Graham

[Scott Dorsey]

Mike Rivers wrote:
Amplifiers are amplifiers. Some sound better than others. There's
nothing magic about a Class A amplifier, but it sure sounds good on the
marketing literature. Most people have the good sense to not use a
Class C amplifier for high quality audio.

You'll find most of the fancy "Class D" amplifiers do in fact have an
ordinary class C output stage before the integrator.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Phil Allison]

"Eeyore"

In fact I've a sort of grudge to bear in fact.


** So THAT is what " Eeyore " really is -

a bear with some sort of grudge ??






........ Phil

[Trevor Wilson]

"Scott Dorsey" wrote in message
...
Trevor Wilson wrote:
"Scott Dorsey" wrote in message
...
Bret Ludwig wrote:
High bias AB amps operate in class A through most of the power range
they spend all their time in, giving the advantage of Calss A operation
where it is needed, and rather than running out of power when this is
exceeded they simply transition into Class B.

This is true. The problem, however, is that although the distortion may
be much lower in class AB than in class B, the distortion spectrum is
often
less pleasant, at least to my ear. I often find a given output stage
sounds
better biased into class B than up higher into class AB.

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my
words:
"Otherwise identical".

That's not what I said. That is not at ALL what I said.

For low power studio-grade applications, though, there's no reason not
to
just go whole-hog and run everything Class A. Electricity is cheap.

**There are plenty of reasons NOT to go pure Class A and very few to do
so.

Other than size and heat?

**Cost, reliability and the fact that high bias Class A/B is lower in
distortion.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Trevor Wilson]

"Scott Dorsey" wrote in message
...
Trevor Wilson wrote:
"Scott Dorsey" wrote in message
...
Bret Ludwig wrote:
High bias AB amps operate in class A through most of the power range
they spend all their time in, giving the advantage of Calss A operation
where it is needed, and rather than running out of power when this is
exceeded they simply transition into Class B.

This is true. The problem, however, is that although the distortion may
be much lower in class AB than in class B, the distortion spectrum is
often
less pleasant, at least to my ear. I often find a given output stage
sounds
better biased into class B than up higher into class AB.

**Bull****. Only poorly deisgned Class A/B amps sound significantly worse
than an otherwise identical Class A amp. Pay careful attention to my
words:
"Otherwise identical".

That's not what I said. That is not at ALL what I said.

**True. What you said was bull****. Now, pay attention to my words. Focus
on: "Otherwise identical". Also focus on: "Poorly designed". If you, like I
have, taken a well designed Class A/B amp and cranked the bias current up to
100 Watts Class A, you will have noted no sonic differences between the
Class A/B operation and the Class A operation. OTOH, I have taken crappily
designed Class A/B amps and cranked the bias up to high levels of Class A
and found significant sonic improvements from doing so.

IOW: The design is more important than the Class of operation. Class A will
help a bad design and, at best, do nothing to a good design.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Eeyore]

Scott Dorsey wrote:

Trevor Wilson wrote:

**There are plenty of reasons NOT to go pure Class A and very few to do so.

Other than size and heat?

That's what I'm working on you see !

Graham

[Eeyore]

Phil Allison wrote:

"Eeyore"

In fact I've a sort of grudge to bear in fact.

** So THAT is what " Eeyore " really is -

a bear with some sort of grudge ??

Long story. Only a small grudge really. I must learn to lie in job
interviews too.

Graham

[Eeyore]

Trevor Wilson wrote:

"Scott Dorsey" wrote
Trevor Wilson wrote:

**There are plenty of reasons NOT to go pure Class A and very few to do
so.

Other than size and heat?

**Cost, reliability and the fact that high bias Class A/B is lower in
distortion.

Lower ?

Graham

[Eeyore]

Trevor Wilson wrote:

IOW: The design is more important than the Class of operation. Class A will
help a bad design and, at best, do nothing to a good design.

You're assuming they all start as Class AB output stages there.

Graham

[Trevor Wilson]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

"Scott Dorsey" wrote
Trevor Wilson wrote:

**There are plenty of reasons NOT to go pure Class A and very few to do
so.

Other than size and heat?

**Cost, reliability and the fact that high bias Class A/B is lower in
distortion.

Lower ?

**Yup. Self has provided convincing proof of this.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Trevor Wilson]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

IOW: The design is more important than the Class of operation. Class A
will
help a bad design and, at best, do nothing to a good design.

You're assuming they all start as Class AB output stages there.

**That's because there are essentially no Class A push pull designs
(anymore). They're all Class A/B with different bias currents.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Trevor Wilson]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message

Have you ever spent any time listening to a true Class A solid
state
amplifiers ?

**We all have. Pretty much every amplifier operates Class A to a
few
tens of milliwatts.

That's not what I meant by true Class A though.

**'True Class A' is a very rubbery definition. A 'True Class A'
amplifier
rated at (say) 50 Watts @ 8 Ohms, will only be 25 Watts Class A, when
driving 4 Ohms, 12.5 Watts @ 2 Ohms, and so on. Given the fact that a
typical 8 Ohms speaker can easily exhibit impedance minima down to 3
Ohms, you'll see the problem.

My understanding of the textbook definition is that the device(s) are
always conducting for the entire cycle i.e. never switch off at all
output
power levels.

**And, unless the precise load is specified, then the definition of Class
A
is meaningless.

It can be specified as a minimum load impedance.

**It can but, IME, never is.



Plenty loud enough for quiet listening. Some high bias Class A/B
designs operate to a couple of Watts in Class A. Even with 90dB/W/M
speakers, this is pretty loud.

Sure enough but what you need to be aware of is that working in the
crossover
region the output device transconductance is varying widely and
putting
non-linearity into the transfer characteristic

**Well, you've managed to narrow your choice of devices down,
significantly,
since the amplification factor of BJTs is expressed as hFE. Current
gain.
The variation in current gain of modern BJTs is spectacularly low,
over
very
wide Collector currents. You need to examine the curves on this page:

http://www.futurlec.com/Transistors/2SC5200.shtml

Pay close attention to the hFE/Ic curves. You'll note that the device
is
linear from 10ma all the way through to 3 Amps.

Current gain doesn't much bother me. It'll be coming from a very low
impedance
stage.

**Current gain SHOULD bother you, since that is what we're discussing.

It's not what I'm discussing.

**It is when discussing what happens to BJTs in an output stage and why
modern BJTs are so linear from a handful of ma up to several Amps.

I've had excellent results with 'super beta'
output stages. Commercial ( pro ) amplifiers simply can't used matched
devices
for practical production and servicing reasons so you design the issue
out.

**Again, not under discussion. For several reasons:
* Pro amps do not operate in Class A.
* Matching output devices is MUCH cheaper than building a pure Class A
amplifier.



The
linearity of the devices is exemplary, over a very wide current range and
down to quite low currents.

For my own part, I am very familiar with an
amplifier which has user switchable Class A operating points. Since
the
design eschews the use of Global NFB, it is far more sensitive to
bais
current changes than most high Global NFB designs. Once the Class A
operating point goes beyond 10 Watts Class A, there is bugger all
difference.

In this case the crossover point has 'moved up the scale' and has
less
overall effect as a percentage of signal level. It doesn't totally
go
away though.

**More bull****. If one goes to the trouble to match output devices,
then,
combined with the excellent linearity I previously mentioned,
crossover
distortion does not exist. It will be swamped by other forms of
distortion and noise.

You can do all this without matched devices.

**Using matched devices eliminates all possiblity of problems.

I don't want to used matched devices. In any case the gm still varies
hugely at
small currents.

**Modern output devices have excellent current linearity over a wide current
range. Design the amp to take that advantage into account.



I simply can't conceive that the
change in gm won't ever have an effect.

**It probably would. However, I am suggesting that modern BJTs have such
excellent current linearity, that no problems will occur when using in
Class
A/B.

That's not my experience. I should point out that I am targeting
*ultra-low*
distortion figures.

**How low? I cannot measure crossover distrotion in any decently designed
amp. All I can see is noise.



Except, when using the thing on a US power receptacle. At 100
Watts Class A, the power consumed from the mains supply is too high
for regular US outlets, without losing mains Voltage.

Really ?

**Yes, really. US 117VAC receptacles are rated for 1,500 Watts. In
reality,
I have measured significant Voltage drops with as little as 1,000 Watt
loads. IMO, it is for this reasona that manufacturers such as Krell
stopped building Class A amplifiers for domestic consumption.

At 100 Watts Class A, in
the US, the sound becomes slightly 'compressed'.

I find some difficulty believing that.

**After you try it, get back to me. US 117VAC power receptacles and
associated wiring is pretty ordinary, compared to almost anywhere else
on
the planet.

How would ac power voltage sag cause a compressed sound ?

**Think about it. Think about it in the context that few power amplifiers
use a regulated power supply.

It's a crappy design that's supply rail sensitive !

**ALL amplifiers which do not use regulated power supplies are rail
sensitive. Which is 99.99% of them.



Pretty much anywhere else
on the planet is fine.


Any comments on how it sounded compared to any other types ?

**IMO, Class A is used by so-so designers who can't figure out how
to
design an amplifier properly. Once bias current is set above the
'knee' of the
device (around 100mA for BJTs and 1 Amp for MOSFETs) any more
Class A bias is superfluous.

There are still some advantages in not turning the devices hard off
though.

**No. However, you can name those alleged advantages, if you wish.

Elimination of switching effects.

**Those effects can be elimintated through the use of matched linear
devices, constant operating temperatures and modest amounts of Class A
bias
current. No full Class A operation is required.

I'm talking about *switching effects* - carrier storage and stuff.

**And again: Matched devices, modest bias current and the problem is solved.



Think of it this way: A badly designed Class A/B amplifier will
probably
sound better when operating in Class A. A well designed Class A/B
amplifier will probably sound slightly worse when operating in
Class
A.

I can't understand the rationale for your 2nd idea there.

**Douglas Self explains it very nicely.

Call me a sceptic then !

**Read Self's work.

I've browsed it occasionally I don't consider him to be especially any
guru
though. In fact I've a sort of grudge to bear in fact.

**Self's description and mathematics are difficult to refute in this area.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Eeyore]

Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:

IOW: The design is more important than the Class of operation. Class A
will
help a bad design and, at best, do nothing to a good design.

You're assuming they all start as Class AB output stages there.

**That's because there are essentially no Class A push pull designs
(anymore). They're all Class A/B with different bias currents.

That's where I plan to differ.

Now. To get back to the original question.... Have you heard a noticeable
difference between Class A and A/B ?

Graham

[Phil Allison]

"Eeyore"

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?



** Transistor car radios made in the 1960s were class A.

They had a 2N301 or similar TO3 pack Germanium PNP power transistor for
output, fed with 12 volts via an iron cored choke.

The speaker connected directly across the choke - it made a small click
when you did.





........ Phil

[Trevor Wilson]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:

IOW: The design is more important than the Class of operation. Class A
will
help a bad design and, at best, do nothing to a good design.

You're assuming they all start as Class AB output stages there.

**That's because there are essentially no Class A push pull designs
(anymore). They're all Class A/B with different bias currents.

That's where I plan to differ.

Now. To get back to the original question.... Have you heard a noticeable
difference between Class A and A/B ?

**Not in a properly designed Class A/B amp. In a poorly designed Class A/B
amp, increasing bias will make it better.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

[Eeyore]

Trevor Wilson wrote:

"Eeyore" wrote in message
Trevor Wilson wrote:
"Eeyore" wrote in message
Trevor Wilson wrote:

IOW: The design is more important than the Class of operation. Class A
will help a bad design and, at best, do nothing to a good design.

You're assuming they all start as Class AB output stages there.

**That's because there are essentially no Class A push pull designs
(anymore). They're all Class A/B with different bias currents.

That's where I plan to differ.

Now. To get back to the original question.... Have you heard a noticeable
difference between Class A and A/B ?

**Not in a properly designed Class A/B amp. In a poorly designed Class A/B
amp, increasing bias will make it better.

So do tell me, what happens to the delta Vbe in an A/B output stage ? ( note its
relationship to current )

Graham

[Eeyore]

Phil Allison wrote:

"Eeyore"

Have you ever spent any time listening to a true Class A solid state
amplifiers ?

Any comments on how it sounded compared to any other types ?


** Transistor car radios made in the 1960s were class A.

They had a 2N301 or similar TO3 pack Germanium PNP power transistor for
output, fed with 12 volts via an iron cored choke.

The speaker connected directly across the choke - it made a small click
when you did.

It *could* have been capacitively coupled had it been a problem of course.

I just discovered in r.a.t that this has been done for SET outputs.

I had something more modern in mind though.

Graham