Interesting info boogiebabies, and nice thread.
Boogiebabies said:
There are a couple of different mods I have noticed and theorized about on JP's amps. The first is a really simple way to add more gain, and different textures of gain.
I've increased the gain in the MkIVB circuit by increasing the value of the plate resistors on V1a+b and V2a (upto 330k!) and now I'm trying different combinations of cathode resistors and bypass caps. It's difficult to have the plate resistor mod switchable due to the high voltages involved (you don't wanna run 400v through a small switch etc). The increase in gain from using different cathode components is marginal but still usable.
Is your high gain mod also on the cathode/anode resistors (or caps? since you a mention different gain structure, and lower cathode bypass cap = more pronounced mids+highs = more sonic impression of gain etc)
I can't work out anything else to do to this circuit, save another cascading gain stage to squeeze more gain out of it
Boogiebabies said:
The second is the second Volume 1 which is a mini MK IV pot that is switched in when the lead channel is engaged, thus allowing him to run a clean channel Vol. 1 at 5 and a Lead channel Vol. 1 at whatever he wants.
So basically this would need a pot to be inserted into the return path from the lead channel, placed before LDR4 to make it switchable when the Lead channel is engaged, right?