Time to look into this again.
The Vox AC10C1 has a LND 150 MOSFET as the input stage, probably "clean" "transparent", going into a bypassed Gain potentiometer, hitting the second stage too hard. Too much gain to soon.
I would like to lower the gain here.
I have no idea how to go about it, other than adjust the Source or Drain resistor values. In this amplifier, the Drain resistor (R95 - "Plate resistor") is a normal resistor, while the two at the Source end (R 62/R63 - "Cathode resistor") are teeny tiny surface mounts.
From a design point of view, will it be better to lower the Drain Resistor (R95), to say, 150 kOhm, easier to do, or up the bypassed Source resistor (R63) to a larger value? Or should I rather up R62, seeing as the gate resistor is 2.2MOhm and adding a bit to R62 should not influence that side too much? And how do I estimate gain from this stage? Drain resistor value divided by Source resistor value?
Another concern is the "fizzy" Top Boost tone, the amplifier does not have a "Tone Cut", and uses small coupling cap values to trim bass output. No lack of Bass though, I'd rather not increase it, so the solution might lie elsewhere? Yes, Tone Cut....
One internet poster says increase Source Resistor value to lower gain, or reduce bypass capacitor value. But, if it indeed biases up like a 12AX tube, working from the "plate" side should also work?
