AMZ presence controls on proco rat?

[innovine]

I'm looking at my spare parts box and think I probably have enough to try the proco rat distortion. But since I don't have the FET, I'm wondering if it'd be possible to use a Big Muff style tone stack, or the AMZ presence control for the tone, and also the Big Muff final transistor to regain volume towards the end?

Can anyone comment on this? Will it work? Will it sound ok? I'll try breadboarding this anway, but if there's some obvious problem, could you please stop me now?

[GGBB]

I'm looking at my spare parts box and think I probably have enough to try the proco rat distortion. But since I don't have the FET, I'm wondering if it'd be possible to use a Big Muff style tone stack, or the AMZ presence control for the tone, and also the Big Muff final transistor to regain volume towards the end?

Can anyone comment on this? Will it work? Will it sound ok? I'll try breadboarding this anway, but if there's some obvious problem, could you please stop me now?

I believe the FET is there as an output buffer, not to provide gain.  As such, any alternative buffer (unity gain) should work fine.  The only thing you might need to worry about is keeping the buffer's 1M input impedance.  Since transistor buffers typically have lower input impedance than JFET, it *may* affect the sound.  But it might not in this circuit since the signal is coming out of an op-amp which have very low output impedance - I'm not sure but I think it will be fine.

[Mark Hammer]

The Rat has a pretty hot output, which is why the FET on the output is a buffer and not a gain stage.  Couldn't tell you just how much passive loss the BMP tone control has, relative to the simple LP filter in a stock Rat, but it's not so much that inserting it would leave you unable to achieve a level noticeably greater than bypass.

If you are cramped for panel space, consider replacing the AMZ presence "control" with a simple 3-position voicing switch.  So, for example, a 24k or 27k resistor to ground, in the same spot as the suggested pot.  Use the 3-position SPDT toggle to either leave the added resistor as is (middle position), shunt it by connecting the 3k3 directly to ground (side position 1) or putting an 18k resistor in parallel with the 24k (or 27k) added resistor for a mild scoop.

Note that reducing the extent of the scoop will also increase apparent level.

[Chugs]

I would suggest looking at the schematic of the Proco Solo which is a Rat with a Muff style tone control with scoop/mids control added.