[beat]

hey all,
is it true that by running amps in class A there is always extra heat produced? if so, why? Just curious.
thanks, beat

[Andrikos]

Oh yeah,
Class A = HEAT!
Not only that but class A in idle (i.e. no music) is MAXIMUM heat!!

The maximum efficiency of Class A topology is 25% but that's just theoretical, practical efficiency is much lower than that, say 10%.
That means for a 100W amp, about 900W of power have to be dissipated as heat through the heatsinks to cool the output transitors down.
So, if you live in the arctic circle and would like to use a space heater, by all means get a class A amp.
If you live in AZ like I do, fuggetaboutit!

[JohnR]

beat, the reason *why* all the heat is because in class A, the output devices are always "on." This means that the "idle" current through them must be greater than the maximum possible current that each device can deliver into the load (ie the speaker). Which means a lot of heat.

In contrast, in class B the output devices are basically "off" with no signal. No current = no heat. When the signal level increases, they source more current and hence dissipate heat.

Not a very good explanation I'm afraid, you sorta need a diagram  

[beat]

Thanks guys,
 I think I get the jist of it. Basically they are acting more efficient when cranking out the tunes..i.e. less heat given off because the power is going into the speakers not just getting sucked into heat sinks because the output devices are on 100% always. Is that the deal?

[markC]

Thanks guys,
 I think I get the jist of it. Basically they are acting more efficient when cranking out the tunes..i.e. less heat given off because the power is going into the speakers not just getting sucked into heat sinks because the output devices are on 100% always. Is that the deal?

I do believe you've got it!