About Push Pull
Push Pull is a program equalizer: a passive filter network that can only take away, a push-pull tube amplifier that makes the loss back, and an output transformer that gives the low end its weight. That order is the whole character. Because the network is passive, boosting and attenuating the same low frequency at once doesn't cancel — the two curves have different corners, so you get a lift with a dip just above it, and a bottom end that reads as bigger without turning muddy.
None of it is approximated with digital filters. The potentiometers, the switched capacitors, the tapped inductor and the bandwidth resistor are entered as a circuit and solved as a circuit every time you move a control — twelve unknowns, re-solved and re-discretised on the fly. Every interaction of a real passive network falls out for free: the low-end trick, the high boost and cut sharing a node, the bandwidth control changing the height of the peak as it changes the width. Component values were fitted to swept measurements to within 0.13 dB across 63 settings.
The amplifier and the iron are modelled with the same care. The tube stage's harmonic levels are calibrated too, and the transformer saturates on flux rather than voltage — which is why it distorts in the bass and stays clean on top, exactly as a real push-pull stage does.
