Attached are schematics from the Audio Research LS7 and LS22. I'm trying to determine to what extent the LS22 is simply a balanced version of the LS7. The circuit looks similar to me, but I don't understand it well enough to grok the implications of the changed values/sections.
The LS22 is a straightforward cascade of stages with local feedback: differential pair, cathode followers, common-cathode stages without cathode resistor decoupling, cathode followers.
The LS7 has local as well as overall feedback, and positive feedback over the second and third stages, and has a most peculiar feedforward from the input differential pair to the other stages. I have no idea what it is for.
The LS7 has local as well as overall feedback, and positive feedback over the second and third stages, and has a most peculiar feedforward from the input differential pair to the other stages. I have no idea what it is for.
In the LS22, what’s driving the differential amplification? Is each channel 4 tubes, and each triode does the + or - half of the differential signal?
Almost. The first stage is a differential pair with some common-mode rejection. The rest is just two single-ended circuits, one driven by the positive and the other by the negative signal.