sdrsdrsdr, not only is your analysis of these amps incorrect but now that I look at it, North Audio's analysis is also severely flawed.
BTW, I read the manual and he never claims it is not push-pull.
Their amps can only be used with a fully balanced pre amp. They take the + and - and amplify individually
This has nothing to do with being push-pull or not. Push-pull amps that can accept a single ended signal must do the inversion inside the amp. His amp simply omits the inverter and thus can only accept a preamp that has done it already or passed through a balanced signal from a source.
They take the + and - and amplify individually. They come together at the output transformerwhere and the noise cancelling happens. This is not push-pull. Any tech nuts out there that might have better understanding of this.
I have been involved with electronics for about 30 years including teaching it at the AAS degree level for 10 years which included amplifier circuit theory. This is as push-pull as you can get.
It is a bit unusual in that it appears the output tubes are biased class A where-as most use class AB, but VAC uses a similar scheme with 300Bs and I assume others do too.
His analysis is way off.
He talks about it takes 4 times as much power to be twice as loud because power is a squared relationship, and then tries to use the P = (V squared) divided by R formula to prove it. That makes no practical sense. The formula is correct, doubling voltage does quadruple power, but this does not prove in any way that it takes four times as much power to be twice as loud.
These statements from his manual are also wrong
The distortion from each single-ended power amplifier is identical in shape, magnitude and in phase in relation to each single-ended amplifier AND the distortion and noise which are kept on the same phase because the two amplifiers are identical AND Everything got cancelled out!
This is simply not true.
The only thing that cancels is noise that is picked up identically by the + and - input signals, and even this can only happen if everthing in both phases is EXACTLY the same as everything in the other phase. It will cancel the majority of this noise but not everything.
The noise generated by a particular tube or other component is completely random in nature, so the noise from the two output tubes cannot be equal amplitude and in phase and therefore will not cancel.
The output tubes are also being fed music signals of opposite polarity. The distortion components will have a phase relationship determined by the polarity of the input signal so the distortion will be out of phase just like the music signals are and will not cancel.
In other words, this guy is either a BS artist or doesn't understand his own circuit. It may sound fine but it doesn't do what he claims.
