Tone Stacks and J201 distortion pedals

Frequent asked about building blocks: gain stages, buffers, clipping configurations, ...
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Post by richard44 »

This question is about Marshall or Fender style tone stacks in JFET distortion pedals, specifically those which have sequential J201 stages.

The J201 gain stages are always in the common source configuration designed to give amplification and clipping. In some designs one of the later stages is a common drain (source follower) which is designed not to boost, but to buffer and have a high impedance in and a low impedance out.

I've read that:
a) a common source JFET stage has a higher output impedance (less optimal), while the common drain has a lower impedance output; and that,
b) tone stacks can load down and suck the life out a signal.

Furthermore, I have either seen it written, or seen schematics which imply that:
a) tone stacks should be preceded by a common drain stage (a la Dr Boogie),
b) tone stacks should be followed by a common drain stage (a la 5150 inspired design),
c) tone stacks should be followed by another common source gain stage (a la Wampler Pinnacle).

So if I were to think of designing an "optimal" distortion pedal using J201 stages, where should the tone stack be placed with respect to the two types of J201 stages?

Another consideration might be to end the chain (i.e., effect's circuitboard) in a common drain stage to ensure the effect has a low Z out and signal does not get lost down the chain to the next effect or amp.

Thanks for any insights.

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