what obvious perceived sound quality segments found in Class A compared to AB? - diyAudio
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Old 22nd December 2012, 06:44 PM   #1
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Default what obvious perceived sound quality segments found in Class A compared to AB?

I just once listened to the Plinius Class A SA-100 amp and was blown away by its dynamics but it was almost a dacade ago never had a chance to listen to class A. I am in the process of building a 25W class A push pull amp but after reading the passgroup I was so curious that what actually is the perceived quality in class A.. Its said to be pure but what are the obvious sonic differences either in mid or High can anybody put a comparision in some listening instrument wise or whatever to describe in simple statements...
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Old 22nd December 2012, 08:40 PM   #2
Zen Mod is offline Zen Mod  Serbia
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imagine Steve McQuin , in his Bullitt Mustang , cruising at 30mph
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Old 22nd December 2012, 09:05 PM   #3
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Zen Mod View Post
imagine Steve McQuin , in his Bullitt Mustang , cruising at 30mph
Hi,

Not a bad analogy. A sense of effortless power, but unfortunately only
at low power. I tried a class A in my system, sublime at low volume,
but it simply couldn't cut the mustard at reasonable levels with bass.

Pity, as it was oustandingly good otherwise. Kelvin Labs I recall.
God awful phono MC/MM stages though, very nice power amplifier.

rgds, sreten.
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Old 22nd December 2012, 09:30 PM   #4
jcx is offline jcx  United States
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well you can get Class A amps at higher power level too, some that stay Class A for lower Z loads - gets noticed on your power bill

Class AB can have low level crossover artifacts - like a sticky clutch
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Old 22nd December 2012, 09:36 PM   #5
Pano is offline Pano  United States
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I've heard Class-A at very high levels and they had no problem at all, quiet the contrary.
Depends on the amp - and the power supply.

Since a Class-A is burning up at least at much power at idle as it will supply to the speakers, the power supply doesn't see much variation in draw. That, IMO, is much of what adds to the sense of stability and power that Class-A amps tend to have. As Zen said about Steve and his Mustang.

There are other advantages, of course. Such as the lack of crossover distortion - you can read about that in many articles across the web.
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Old 22nd December 2012, 09:48 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

The amp I tried was 20W proper push pull class A, of course you can go bigger.
At low power it sounded immense, like it had unlimited power, but it doesn't.

rgds, sreten.
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Last edited by sreten; 22nd December 2012 at 09:50 PM.
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Old 22nd December 2012, 09:50 PM   #7
Pano is offline Pano  United States
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At the expense of heat, of course!
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Old 22nd December 2012, 10:44 PM   #8
Zen Mod is offline Zen Mod  Serbia
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obvious problem in Sreten's system is usage of wrong speakers

whatever - when one can say that A class amp is really good , usually amp in question is simple in construction , having pleasant THD spectra.
that , besides lack of xover distortion , almost constant PSU loading/modulation ..... is resulting in nice sounding amp

I had opportunity to listen PL SR1 , driven with pair of PL XA60.5 ; SR1 aren't in league of efficient spks , even if having benign impedance module ; sound was flawless - maybe not exactly my cup of tea , but certainly sound which I want for one of my rooms



something to read : http://www.firstwatt.com/pdf/art_leave_classa.pdf
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Old 22nd December 2012, 11:55 PM   #9
max426 is offline max426  United States
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Quote:
Originally Posted by jcx View Post
......
Class AB can have low level crossover artifacts - like a sticky clutch
aha, thats where the "klunk" comes from
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Old 23rd December 2012, 01:20 PM   #10
Telstar is offline Telstar  Italy
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Funny thing that the OP talked about Plinius. I once heard a model which could switch between class A and class AB... short story, the AB had correct timbre, while in class A mode it was colored. Really strange behaviour.

For a general purpose amp, a heavily biased AB push-pull is probably the most "sound" (pun intended) option. With a bias as high to reach the crossover point only on the strongest music transients. The PSU would be a real challenge, especially if we want to regulate it or use chokes.
For a fixed class A operation psu while expensive is much easier to make, and we have several good examples in this very forum.

I have no idea what Plinius did wrong in its class A mode, but it's definitely not my reference.

Note that I find some coloration in all mosfet class A amps I heard, included PL and my little F3. My tastes are more for paralleled BJTs with very high current and a more neutral sound. YMMV.
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