Class AB with Regulated Power Supply...Class A-like? - Page 2 - diyAudio
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Old 20th January 2013, 08:55 PM   #11
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Quote:
Originally Posted by djoffe View Post
Sreten...You're absolutely right...the high current drain of the class A amp will produce more AC mains based ripple all the time. To clarify my point, it is that the the class A amp produces no signal-based ripple on the supply rails.
Actually most class A amps do draw a signal-dependent current from the supply. Unlike a class (A)B amp, they do not draw a half-wave rectified signal current from the supply, but a more or less undistorted signal current superimposed on a big DC current.
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Old 20th January 2013, 09:04 PM   #12
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Originally Posted by Boscoe View Post
I really don't know why everyone raves on about class A and it's linearity, I've never seen a class A amp good in distortion they are usually terrible. Class AB is superior in every way unless you want a heater.
If you bias your amplifier into class A, away from an optimally biased class AB and you don't see a reduction in distortion, then you need to go back and redesign your amplifier. I agree with you however that most class A amps, when measured, don't even come close to blameless performance. Providing this is intentional, ie circuit/design choices, rather than unintentional, ie bad layout, then I don't see a problem.
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Old 20th January 2013, 09:09 PM   #13
DF96 is offline DF96  England
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Marcel (post 11) is right. Class A does not have constant current draw. It has constant average current draw (averaged over a complete cycle), provided that there is no even-mode distortion. The difference between A and AB relates to how the average current draw varies with signal envelope; both take instantaneous currents which contain signal components.
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Old 20th January 2013, 09:13 PM   #14
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A single ended class A would have a constant current draw though right?
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Old 20th January 2013, 09:20 PM   #15
DF96 is offline DF96  England
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SE Class A with a choke or CCS load could have constant current. I hadn't thought of that.

Given that most decent power supplies can cope with varying currents, and may even work better at low currents, there seems little point in aiming for constant current draw.
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Old 20th January 2013, 09:40 PM   #16
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Quote:
Originally Posted by djoffe View Post
Sreten...You're absolutely right...the high current drain of the class A amp will produce more AC mains based ripple all the time. To clarify my point, it is that the the class A amp produces no signal-based ripple on the supply rails.
Also a classA amp produces signal based ripple on the supply rails, it is just that as a proportion of total current drawn it is less than classAB.

edit: Sorry, missed page two of the thread, see point has already been made in abundance

Last edited by vacuphile; 20th January 2013 at 09:42 PM.
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Old 20th January 2013, 10:40 PM   #17
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Boscoe View Post
I really don't know why everyone raves on about class A and it's linearity,
I've never seen a class A amp good in distortion they are usually terrible.
Class AB is superior in every way unless you want a heater.
Hi,

Well perhaps you need to look harder. Well designed class A is better
than class aB but hideously inefficient. Class AB has a lot going for it.
(In my book aB is optimum bias, AB is high bias partial class A).

An interesting approach is designing for class aB but manipulating
the circuit such that the optimum bias current is relatively very high.
Multiple output devices and low Re's (or no Re's) are needed.

rgds, sreten.
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Last edited by sreten; 20th January 2013 at 10:43 PM.
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Old 21st January 2013, 01:05 AM   #18
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Boscoe View Post
Class AB is superior in every way
Yes, except in sound quality

BTW, there is no class-AB in this context. It's A or B.
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Old 21st January 2013, 01:46 AM   #19
chicks is offline chicks  United States
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Dynaco used a regulated supply in their class AB Stereo 120 amp. Did they just not know at the time how to get good enough PSRR, requiring the regulation?
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Old 21st January 2013, 09:59 AM   #20
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Originally Posted by 6L6 View Post
One of the challenges is that as the amp gets bigger, the regulator for the PSU is almost as big (or sometimes bigger!) than the amp itself.
I know the above is done but...Dosent the benefit come from regulating the supply for the driver stage back? i.e there is no benefit from a regulated supply for the output stage unless the amp is run into clipping?

EDIT: For an AB amp.
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