Which small class A P-P design to build?


2008-06-09 6:34 pm

I'm wondering if I should try out the benefits of class A operation. The thing is, if I decide to keep what I build, it needs to be medium powered and moderately efficient, which implies P-P operation.

One special case is Douglas Self's class G design, of which I have heard that it's possible to run the lower supply voltage in class A.

So basically I have two and a half questions:
1. Are there any nice and small passively cooled class A P-P designs with +/-16 to 25 V power supplies?
2. Has anyone built the Self's class G amplifier, and then run the smaller supply in class A?


2008-06-09 6:34 pm
Pass A40, my shop winter amp.


Preferably something less powerful, because I'd use it also during our moderately hot summers and I have no air conditioning. The A40 has +/-32 V rails. Even getting down to +/-25V would be nice.

I've heard that the Self's class G amplifier has the advantage that one can switch easily between A and AB classes for the lower supply.

The A40's peak output is calculated as 25.3 V into 8 Ω, which is 3.16 A (the bias times two), also 80 W (for 100 W dissipation per channel). Now 25 V rails would maybe give 18 V peak output, which is 2.25 A into 8 Ω and therefore 40 W. Requiring a 1.2 A bias, resulting in 60 W dissipation per channel.

With Self's class G amplifier I could use +/-21 V from a +/-15 V transformer and have the other rail for peak needs.


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2003-07-25 10:44 pm