Why do class A amps gennerat so much heat ?
That's the question
Pishanto Specialist & Super-Daftee
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I'm Allen.
Class A amps ?
Why do class A amps gennerat so much heat ?
That's the question
[
Moderator & Terminator!
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I'm Geoff.
'Cos they operate at near full power at all times.
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Captain Insightful
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I'm Dennis.
They have a very high quiescent current and only approach 45% efficiency, and their superiority, which was once evident, is now becoming much less so as other configurations have improved.
Audio Engineer; Moderator
Location: South Wales
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I'm NotTakingLifeTooSeriouslyTheseDays.
As Geoff stated they draw all the current they need for full output all of the time, whether you are modulating them with signal, or not, Conventional Single ended is inherently Class A, as its using one device [or a few in parrallel] to conduct both halves of the cycle, hence its fully switched on, all of the time. With push-pull output stages, where they share the full cycle between them, they can be biased anywhere between class A, and class B, eg; A, AB1, AB2, etc, etc.
A...
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I'm Lawrence.
The advantages of this being that the moment they need the power on a transient it's there ready and waiting, whereas with a class AB it's got to draw that current on demand. I've often wondered whether that "asking" for the current, with an inherent tiny delay and build up to the required current, causes a loss of attack in the transient, a slight delay and hence possible phase issues, or just distortion in some way (I'm not talking about the distortion in a push-pull configuration here which is a different kettle of fish, though maybe related).Originally Posted by walpurgis
The other thing I've thought about is that, given that delay is presumably rather short, the benefits of class A will probably be felt more at the higher frequencies like cymbals and maybe voices as any timing "delay" will have more impact there. It's more like to sound "natural".
I should stress this is all the result of thinking logically about it with little knowledge and no training in electronics and circuits.
The reason why they run hot is that when there is no/low volume the energy drawn has to go somewhere so it is dissipated as heat. I once read it will run cooler the louder you play it, which makes sense.
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Pishanto Specialist & Super-Daftee
Location: Dagenham Essex
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I'm Allen.
OK thanks , so I assume they are built with components that can stand the constant considerable heat all the time ?
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Super Moderator
Location: W Lothian
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I'm Grant.
they can be seen by their enormous heat sinks usually... well the ones that do a lot of class A have big uns
mf a1000 does 50w and has huge uns... they get very toasty
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I'm inthescottishmafia.
Usually yes, consider all the vintage Krells and the like still in use, though most have been recapped at least, but that's due to age more than any other reason.
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Hunter S Thompson
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I'm Shaun.
One would hope so. My present amp is heavily biased into Class A and gets very warm but not what I would refer to as hot. Lovely sound though. Just need a comparable preamp now.
Senior Member
Location: Bristol
Posts: 6,843
I'm Justin.
Well my Luxman certainly doesn't get cooler the louder you play it. It's good for 120 Watts class A into my 4 Ohm speakers. That's quite a lot of class A.
Hearing both my Luxman and the large class A Sugden amps they appear to share a sense of relaxed ease in the way they deliver music that evades class A/B designs.
BTW while the Luxman gets hot it's noting compared to my 211 monoblocks.
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