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Class A vs Class AB

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Analog Kid View Drop Down
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    Posted: 19 Nov 2008 at 5:43pm
As a guitar player I greatly prefer the sound of class A valve guitar amplifiers. The guitar valve amplifier I had to sell to buy my Reflex, had a switchable class A mode. In class A it sounded warmer, sweeter and more organic than in class AB. It was a much nicer and more pleasant sound.

What about for HiFi amplifiers, is there a significant audible difference between class A and AB amps? Does class A also sound better in HiFi?

And why don't HiFi amps have a switchable class mode like some guitar amps? Is this not possible to implement?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mrarroyo Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 2008 at 11:10pm
The one feature from guitar amps that I wished was available in home stereo tube amps is the "standby switch". I have not seen one in home tube amps, yet.
Miguel
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Analog Kid Quote  Post ReplyReply Direct Link To This Post Posted: 15 Mar 2009 at 10:00pm
Originally posted by Analog Kid Analog Kid wrote:

What about for HiFi amplifiers, is there a significant audible difference between class A and AB amps? Does class A also sound better in HiFi?

And why don't HiFi amps have a switchable class mode like some guitar amps? Is this not possible to implement?



Do any of the amplification experts on the forum want to offer their answers for the above questions? I am still curious to learn more.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 15 Mar 2009 at 11:44pm
Forcing Hi-Fi amps to get hot by moving the bias into class A quarters can help get rid of the "transistor sound", but I think sometimes it is a crutch.

The transistor sound is usually because of instability - messing about with increased bandwidth can take a design to the edge of high frequency instability - and that should also answer why things sound bright.

What made matters worse was the RoHS - many components lost much of their warm character with the removal of alleged hazardous substances.

From my point of view, rather than pushing bandwidth (taking pole splitting techniques to extremes), with RoHS it's about bringing bandwidth down very slightly to buy a bigger stability margin. In my opinion this gives better results than class A bias.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Analog Kid Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2009 at 8:19pm
Maybe the best way to get rid of the "transistor sound" is to replace the transistors with valves. Tongue
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2009 at 11:49pm
Originally posted by Analog Kid Analog Kid wrote:

Maybe the best way to get rid of the "transistor sound" is to replace the transistors with valves. Tongue


I guess they'll all have to do that eventually...

...then I'll get ALL their sales! Evil%20Smile

(who dares wins)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Analog Kid Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2009 at 6:40pm
This question still remains, so I will try again: is it not possible to design a HiFi power amplifier, either valve or solid-state, that can be switched between Class A and Class AB at the flick of a switch? Never seen this in a HiFi amplifier before, but in guitar amplifiers it is a quite common feature.
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