pre65 wrote: ↑Fri Apr 28, 2017 4:51 pm
It runs hotter because one of the mosfets on each amp is a CCS.
Because of that it runs hotter (dissipates more) than if it had a inductive load, but if you do the calculations for a real 50 class A push pull amp.
To product a 50W signal into 8R that will need a 20v RMS signal.
a 20v RMS signal is a 28v peak signal voltage.
28v into 8R will pass a current of 3.5A
If its to stay in A up to full power, it needs to be passing at least 3.5A to the output devices, which it would be passing all the time.
so you need a pair of rails at +28v and -28v, and a current of 3.5A (assuming no losses). So the dissipation at idle will be (28+28)*3.5 = 196W
So a real class A push pull amp producing 50W into 8R will be dissipating 196W, so about the same as Phils amp.
Ergo. if the MF50 is not this hot, its not a 50W class A amp.
Not that it has to, my P6 mosfets are in class A up to 16W (2A idle current), I would deify anyone to hear (or for that matter measure) that point where they change into B. In reality very very few push pull amps are either just A or just B.
The CCS in Phils amp, is (one could claim) making it act just like a push pull amp.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.