motterpaul wrote
Thank you Frank. The circuit DOES need to be brighter and that looks like a good solution.
I tried changing the 4.6n to 1n, but in my case it caused the FET design to underpower one of the gain stages, so the notes didn't have enough attack. It also didn't really make the tone knob work, it just changed the frequency response of the circuit. It did stop the switch from making the amp die out, though.
I ended up just removing (and jumpering) the tone control pot and now it sounds decent but it could be brighter.
The 'tone' control in this circuit comes before the last gain stage, which means it's more likely to control the character of the distortion rather than the frequency response of the circuit as a whole (which is what it would do if it came after all of the clipping stages). Cutting out high-end before a clipping stage is a common way to shape the distortion to sound more 'vintage', but I'm not surprised it kills the attack. That's pretty much what I'd assume it's supposed to do from the circuit topology.
If you just want the circuit to be brighter, I agree, a BMP tone stack will get you there (at the expense of losing some bass). But I'd tack it on the end of the circuit, after all of the existing gain stages. The BMP tone stack is pretty lossy, though. So you may need a make-up gain stage after it (I think there's a daughter-board vero for this very purpose on the forum somewhere?). Try it on the breadboard and see how it works for you. You can adjust the components to customize the response of the tone control with the Duncan Tone Stack Calculator, which is a free download, assuming you don't already have it.
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