A Audio and hi-fi forum. AudioBanter

Go Back   Home » AudioBanter forum » rec.audio » Tech
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Any blind listening tests on Class A vs Class B amps?



 
 
Thread Tools Display Modes
  #1  
Old September 3rd 05, 07:11 AM
Don Pearce
external usenet poster
 
Posts: n/a
Default Any blind listening tests on Class A vs Class B amps?

On Fri, 02 Sep 2005 22:38:33 -0700, hoarse with no name wrote:

> Class A amps seem to be universally considered to provide better sound
> than Class B amps. Has this ever been put to a real test?


As far as I am aware, there are no class B amps around these days. Anybody
know of any?

d
Ads
  #2  
Old September 3rd 05, 08:16 AM
Stewart Pinkerton
external usenet poster
 
Posts: n/a
Default

On Fri, 02 Sep 2005 22:38:33 -0700, hoarse with no name >
wrote:

>Class A amps seem to be universally considered to provide better sound
>than Class B amps.


Not in this Universe! :-)

>Has this ever been put to a real test?


Yes, and even into a very tough but highly transparent load (Apogee
Duetta Signatures), my pure Class A Krell KSA-50 mkII sounds identical
to my low-bias Class AB Audiolab 8000P.

The only significant difference for the DIY enthusiast is that it's
quite difficult to make a traditional Class A amplifier that sounds
bad, this is not so true of Class AB, where many pitfalls await the
unwary constructor. Ultimately, there are many more important things
about amplifier design than mere class of operation.

--

Stewart Pinkerton | Music is Art - Audio is Engineering
  #3  
Old September 3rd 05, 08:17 AM
Stewart Pinkerton
external usenet poster
 
Posts: n/a
Default

On Sat, 3 Sep 2005 07:11:16 +0100, Don Pearce >
wrote:

>On Fri, 02 Sep 2005 22:38:33 -0700, hoarse with no name wrote:
>
>> Class A amps seem to be universally considered to provide better sound
>> than Class B amps. Has this ever been put to a real test?

>
>As far as I am aware, there are no class B amps around these days. Anybody
>know of any?


No, but most amateurs describe Class AB amps as Class B. There's no
real confusion here, I think.
--

Stewart Pinkerton | Music is Art - Audio is Engineering
  #4  
Old September 3rd 05, 09:11 AM
Don Pearce
external usenet poster
 
Posts: n/a
Default

On Sat, 3 Sep 2005 07:16:14 +0000 (UTC), Stewart Pinkerton wrote:

> On Fri, 02 Sep 2005 22:38:33 -0700, hoarse with no name >
> wrote:
>
>>Class A amps seem to be universally considered to provide better sound
>>than Class B amps.

>
> Not in this Universe! :-)
>
>>Has this ever been put to a real test?

>
> Yes, and even into a very tough but highly transparent load (Apogee
> Duetta Signatures), my pure Class A Krell KSA-50 mkII sounds identical
> to my low-bias Class AB Audiolab 8000P.
>
> The only significant difference for the DIY enthusiast is that it's
> quite difficult to make a traditional Class A amplifier that sounds
> bad, this is not so true of Class AB, where many pitfalls await the
> unwary constructor. Ultimately, there are many more important things
> about amplifier design than mere class of operation.


True enough. Provided both amplifiers are competently designed, there is no
audible difference. The big difference between A and B (or AB) is that I
really don't want to be using a Class A amp during the summer.

I've just had a quick read through Doug Self's book on this subject, and
his view (which he supports very persuasively) is that Class A is not the
panacaea to linearity that many believe it to be.

d
  #5  
Old September 3rd 05, 10:14 AM
Stewart Pinkerton
external usenet poster
 
Posts: n/a
Default

On Sat, 3 Sep 2005 09:11:53 +0100, Don Pearce >
wrote:

>On Sat, 3 Sep 2005 07:16:14 +0000 (UTC), Stewart Pinkerton wrote:
>
>> On Fri, 02 Sep 2005 22:38:33 -0700, hoarse with no name >
>> wrote:
>>
>>>Class A amps seem to be universally considered to provide better sound
>>>than Class B amps.

>>
>> Not in this Universe! :-)
>>
>>>Has this ever been put to a real test?

>>
>> Yes, and even into a very tough but highly transparent load (Apogee
>> Duetta Signatures), my pure Class A Krell KSA-50 mkII sounds identical
>> to my low-bias Class AB Audiolab 8000P.
>>
>> The only significant difference for the DIY enthusiast is that it's
>> quite difficult to make a traditional Class A amplifier that sounds
>> bad, this is not so true of Class AB, where many pitfalls await the
>> unwary constructor. Ultimately, there are many more important things
>> about amplifier design than mere class of operation.

>
>True enough. Provided both amplifiers are competently designed, there is no
>audible difference. The big difference between A and B (or AB) is that I
>really don't want to be using a Class A amp during the summer.
>
>I've just had a quick read through Doug Self's book on this subject, and
>his view (which he supports very persuasively) is that Class A is not the
>panacaea to linearity that many believe it to be.


Yes, I swithered as to including Self's 'blameless' Class AB designs
in my post, but erred on the side of brevity - for a change! :-)

While a Class A PP design has no switching discontinuity, it certainly
can have 'crossover distortion' in the sense of nonlinearity of
transfer function. As Self points out, a *carefully* designed Class AB
output stage can have an optimised bias point which makes it even more
linear than an equivalent Class A design. I have designed and built
several amps on this principle, using Hitachi MOSFETs biased at 120mA
per device.
--

Stewart Pinkerton | Music is Art - Audio is Engineering
  #6  
Old September 4th 05, 10:25 AM
Tim Martin
external usenet poster
 
Posts: n/a
Default


"Don Pearce" > wrote in message
...

> As far as I am aware, there are no class B amps around these days. Anybody
> know of any?


Presumably this "high end audio manufacturer" makes Class B amplifiers:

http://www.norh.com/docs/amps/

"... 99% of all audio amplifiers today are Class B. Class B amplifier can be
built today so that its distortions are well below what the human ear can
detect and nearly to the point where it is unmeasurable.
Many amplifiers call themselves Class A/B. In reality, very few are. Early
Class B amplifiers had a problem known as switching delay. In a class B
design, a transistor works 50% of the cycle while another transistor works
50% of the cycle. In early class B amplifiers, there was a distortion
created between the time the devices were switching back and forth. Some
people referred to this distortion as notch distortion because there was a
notch appearance on an oscilloscope between the two waveforms.

Class A/B was created to leave the transistor conducting while the second
transistor was conducting. This created an overlap between the two signals.
The problem with this approach is that it created its own distortion called
gumming. This means that the signal would get a little fatter where the two
devices were both conduction.

Today, if you look at a properly designed Class B amplifier on a scope, you
will see no switching distortion."




  #7  
Old September 4th 05, 10:44 AM
Don Pearce
external usenet poster
 
Posts: n/a
Default

On Sun, 04 Sep 2005 09:25:27 GMT, Tim Martin wrote:

> "Don Pearce" > wrote in message
> ...
>
>> As far as I am aware, there are no class B amps around these days. Anybody
>> know of any?

>
> Presumably this "high end audio manufacturer" makes Class B amplifiers:
>
> http://www.norh.com/docs/amps/
>
> "... 99% of all audio amplifiers today are Class B. Class B amplifier can be
> built today so that its distortions are well below what the human ear can
> detect and nearly to the point where it is unmeasurable.
> Many amplifiers call themselves Class A/B. In reality, very few are. Early
> Class B amplifiers had a problem known as switching delay. In a class B
> design, a transistor works 50% of the cycle while another transistor works
> 50% of the cycle. In early class B amplifiers, there was a distortion
> created between the time the devices were switching back and forth. Some
> people referred to this distortion as notch distortion because there was a
> notch appearance on an oscilloscope between the two waveforms.
>
> Class A/B was created to leave the transistor conducting while the second
> transistor was conducting. This created an overlap between the two signals.
> The problem with this approach is that it created its own distortion called
> gumming. This means that the signal would get a little fatter where the two
> devices were both conduction.
>
> Today, if you look at a properly designed Class B amplifier on a scope, you
> will see no switching distortion."


I don't put too much store by that article. In fact I believe it is
entirely backwards in that many amplifiers that call themselves class B are
in fact class AB. Even a milliamp of bias current in the output devices is
enough to make this true, and holding an output pair at exactly zero bias (
no reverse bias or forward bias) is really hard - far easier to allow just
a little forward bias to ensure that the true horror of both transistors
turning off at the mid point can be avoided.

As for seeing switching distortion on a scope - well, if you could do that
you would have an amplifier of unimaginable horror. This statemenrt also
leads me to believe that this article is not written with great technical
expertise. Bujt then you say that this is a high-end audio manufacturer, so
this is no great surprise.

d
  #8  
Old September 4th 05, 12:03 PM
Geoff Wood
external usenet poster
 
Posts: n/a
Default


"Tim Martin" > wrote in message
...
>
> "Don Pearce" > wrote in message
> ...
>
>> As far as I am aware, there are no class B amps around these days.
>> Anybody
>> know of any?

>
> Presumably this "high end audio manufacturer" makes Class B amplifiers:
>
> http://www.norh.com/docs/amps/
>
> "... 99% of all audio amplifiers today are Class B. Class B amplifier can
> be
> built today so that its distortions are well below what the human ear can
> detect and nearly to the point where it is unmeasurable.



I would not buy anything of a "high end audio manufacturer" who does not
evidently understand what most spotty electronic geek students learn in
their first semester (if they didn't know already).

geoff


  #9  
Old September 4th 05, 11:38 PM
Arny Krueger
external usenet poster
 
Posts: n/a
Default

"Tim Martin" > wrote in message

> "Don Pearce" > wrote in message
> ...
>
>> As far as I am aware, there are no class B amps around
>> these days. Anybody know of any?

>
> Presumably this "high end audio manufacturer" makes Class
> B amplifiers:
>
> http://www.norh.com/docs/amps/



> "... 99% of all audio amplifiers today are Class B.


Absolutely totally and completely false.

Here is a true statement:

99.99% of all audio amplifiers today are Class AB

> Class B amplifier can be built today so that its
> distortions
> are well below what the human ear can detect and nearly
> to the point where it is unmeasurable.


Nope, a true class B amplifier is rare thing because it
depends on precise biasing that cannot be controlled well
enough.

> Many amplifiers call themselves Class A/B.


Yes, and there's nothing wrong with that.

> In reality, very few are.


The author is living in an alternative universe.

> Early Class B amplifiers had a problem
> known as switching delay.


Some did.


>In a class B design, a
> transistor works 50% of the cycle while another
> transistor works 50% of the cycle. In early class B
> amplifiers, there was a distortion created between the
> time the devices were switching back and forth. Some
> people referred to this distortion as notch distortion
> because there was a notch appearance on an oscilloscope
> between the two waveforms.


This would be true except that almost zero SS amps have been
built this way.

> Class A/B was created to leave the transistor conducting
> while the second transistor was conducting. This created
> an overlap between the two signals.


So far so good.

>The problem with this
> approach is that it created its own distortion called
> gumming.


I've heard of a lot of weird stuff, but I've never heard of
gumming distortion.

> This means that the signal would get a little
> fatter where the two devices were both conduction.


Spare me!



> Today, if you look at a properly designed Class B
> amplifier on a scope, you will see no switching
> distortion."


Probably, you will because true class B is a single, very
exact point and its hard to hold.


  #10  
Old September 5th 05, 06:05 AM
Don Pearce
external usenet poster
 
Posts: n/a
Default

On Sun, 4 Sep 2005 18:38:51 -0400, Arny Krueger wrote:

>>The problem with this
>> approach is that it created its own distortion called
>> gumming.

>
> I've heard of a lot of weird stuff, but I've never heard of
> gumming distortion.


Hee hee! I think he is perhaps referring to Gm doubling during the phase
when both output trannies are conducting.

d
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
phase splitter NGS Vacuum Tubes 40 May 22nd 05 03:17 AM
Sub Amps - a Follow up Question T Tech 26 April 29th 05 05:26 PM
science vs. pseudo-science ludovic mirabel High End Audio 91 October 3rd 03 09:56 PM
Why DBTs in audio do not deliver (was: Finally ... The Furutech CD-do-something) Bob Marcus High End Audio 313 September 9th 03 01:17 AM


All times are GMT +1. The time now is 12:30 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright 2004-2020 AudioBanter.
The comments are property of their posters.