Technical curiosity about push-pull amps...

[ytse_jam]

in these days i took the time to read the article by randall smith about class A amplifiers. There's a point in which he says in a class AB push-pull poweramps the second distortion harmonic is cancelled due to the fact it is symmetrical even in the two signals of opposite phase (so it's cancelled in the same way of noise)... so what's the waveform of this harmonic, since it must be the same even if 180 degrees out of phase from itself? does it happens in Class A push-pull too? if not, why? I'm sure many things i said are wrong and i have got a big confusion in my mind, so could anyone explain to me this? thanks!

 

[blindsirens]

He's just trying to explain why there are tonal and distortion differences between a single ended power section and a push-pull power section. This noise/distortion cancellation effect happens in any push-pull set up whether its class A or class AB. When your signal goes into clipping it generates notes octaves above the fundamental note and I believe the second harmonic is one octave up. He goes on to say the third harmonics are more dominant in push-pull when driving into clipping distortion. I've heard single ended and its a sound only certain folks would be into and some might not notice a difference at all.

 

[ytse_jam]

btw, am i wrong, or the fundamental note is a half sinus waveform? so the second harmonic, being an octave up and so twice the frequency of the fundamental, should be a complete waveform, right? or is it this second one that is the fundamental since it's the first complete waveform???


so, in a push-pull poweramp you'll have two opposite-phase signals. One is then recounducted in phase with the other and noise is cancelled because it is in phase in the two branches of the circuit and when you invert the phase it ends up being out of phase, right? So, if this second harmonic produced during clipping is cancelled in push pull amps, could the reason be that, even if the two fundamental waveforms are out of phase in the two branches, they produce an in-phase second harmonic during clipping? it seems strange to me, but i'm definitely not an expert and i would like to know how the real thing works!

 

[ytse_jam]

and, btw... what are the frequencies in the voltage output signal coming from a guitar when you play a single note? i believe they are already many more than just the fundamental... how could the fourier transform of that signal look (intensities of the various frequency components)?

 

[oyster]

yes :?

 

[ytse_jam]

yes :?

really? :shock:

 

[Elpelotero]

i highly recommend everyone reads this manual. you may have to read it twice, and a lot will go over your head at first, but it is very interesting stuff. i learned a lot.