"tony sayer" wrote in message
news
In article m, Mike
Rivers writes

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.

Anyone ever made a good commercially viable class D amp?...

**Sinclair Radionics.

Snicker

Seriously, though, there are *lots* of them. Subwoofer amps are particularly
popular.


--
Trevor Wilson
www.rageaudio.com.au



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

In article , Trevor Wilson
writes

"tony sayer" wrote in message
news
In article m, Mike
Rivers writes

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.

Anyone ever made a good commercially viable class D amp?...

**Sinclair Radionics.

Snicker

Gawd!, remember them when they were in Fitzroy street not far from where
I went to Skool

Bloody thing packed up when you tried to use it when it was going seemed
OK but I wonder if it was a good idea but limited by the available
semiconductors in those days circa 1966 ish!...


Seriously, though, there are *lots* of them. Subwoofer amps are particularly
popular.


--
Trevor Wilson
www.rageaudio.com.au




--
Tony Sayer

In article ,
Trevor Wilson wrote:
In the terms of the question and accepted meaning it was a Class A amp.

**Nope. They only built high bias Class A/B amps. The first Sugden I ever
saw was about 40 Watts/channel.

This one was 25 watts a channel. IIRC, their original design.

It ran bloody hot and people all said it was Class A. I didn't believe
it, so I tested one at 5 Watts Class A. Substantial, but not Class A.
About 100 times more Class A than most amps of the time. It was still
Class A/B though.

My mate reckoned he had measured it and it consumed slightly more current
in a quiescent state than at full output. But I can't check up with him as
he's no longer with us.

--
*Preserve wildlife - Go pickle a squirrel*

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

"Eeyore" wrote in
message

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

I've worked with power amps that had bias pots, and listened to them and
tested them at various bias settings. While the amps lacked heat sinks that
could run class A for any amount of time, I have listened to and tested amps
at power levels where the amp was running in true class A. IOW both halves
of the output stage were conducting all of the time.

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

I never did any DBTs, so my comments about listening aren't all that
authoritative. However, there was no perceptible difference that was IMO
anything like dramatic or even noticable. OTOH class A made the the subtle
hum of the power transfomer louder, the heat sinks needed fans, and it was
quite obvious that lot of heat was being dissipated in the room. Some might
find all that to be exciting.

There also wasn't very much of a measurable difference and the differences
weren't all positive for class A. For example, running an output stage in
class A can increase distortion, because the output devices have to run at
higher current levels, where the output transistors might be far less
linear. For the same reason, running an output stage in class A can
dramatically reduce SOA, leading to a far less durable amplifier. Throwing
output devices at an amplifier is not an exercise that can be continued
indefinately without introducing other problems than just economics.

As my distortion measuring gear progressed to residuals in below 0.01% there
was always a mixed bag of measurable differences. But they were arguably
quite small, given that its often darn hard to hear distortion below 0.1%
or so. Class AB amps with 0.02% or less distortion at typical power levels
are pretty common, these days. For example, the QSC amps that some despise
so much have to be clipping a bit to have nonlinear distortion as high as
0.02%.

In the early days of SS there were problems with biasing SS output stages,
and running class A might have made more of a difference. Simply clamping
the bias regulation diodes and having the right number of them could make a
significant difference. Another fairly strong issue is the fact that the
effective current gain of the output stage is approximately doubled in the
region where both outputs are conducting. (see "gm-doubling" at
http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm#2 ). When output devices
were far slower than they are today, what Self calls "switchoff distortion"
was also an issue.

"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.



** Oh - that job Doug got with Soundcraft ?

He did the power amp stage of their "PowerStation".




....... Phil

"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 ?

Yes, there are two problems with class A - both related to the fact that
with class A, the output stage always has far more current flowing in it.

(1) Power transistors tend to be less linear at high currents - the beta
falls off. Running an output stage class A approximately doubles the
current that the output stage has to handle. So, you move the operating
point way out on the output devices.

(2) Less SOA from the perspective of the load, because the output devices
are pulling so hard against each other.

"Trevor Wilson" wrote in
message
"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.

Agreed.

I would hope that this paper would be required reading for any
self-appointed power amp guru:

http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm

"Trevor Wilson" wrote in
message
"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.

Agreed again. Building a truely Class A power amp that can deliver
significant amounts of power output is really a pretty awesome thing. The
OPT stage quiescent current has to be equal to the *peak* current that is
delivered to the load.

We all know that speakers can be capacitive-reactive and can jack the load
current to unexpectedly high levels. A common power amp will have +/- 80
volt DC rails and may need to deliver up to 15 amps peak to the load. So,
now the OPT is dissipating 2400 watts per channel just sitting there, not
counting internal losses.

Considering that heavy duty electrical room heaters usually top out around
1600 watts, the problem should be self-evident. We're basically talking a
power amp that duplicates the heating function of 3 room heaters and has to
be hooked up to a clothes dryer circuit.

"Eeyore" wrote in
message
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 )

Here's another one of my so-called *evasive* answers:

http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm

"Eeyore" wrote in
message
Don Pearce wrote:

"Bret Ludwig" wrote:
Trevor Wilson wrote:
"Dave Plowman (News)" wrote in
message
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.

Do you mean nonexistent in the region of class B
operation? It is class A that provides the
transconductance doubling because there are two active
devices operating in parallel.

Agreed. It's a real problem, and one that is thus far generally dealt with
indirectly.

I'm concerned about the transconductance 'modulation'
with signal level since this introduces non-linearity.

Again, covered in http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm