Hot cake presence control

[BurntFingers]

I'm searching for a minimal tone control (treble cut/boost) and this caught my eye. If I'm reading the right schematic it looks like it's a 22k pot into a 56n cap, working as a variable low pass filter before it goes to the output.

Is that the essence of it? I see the other rc network beforehand coming off the 741 but don't know if they're controlling the presence or not.

 

[benny_profane]

That 56n cap also interacts with the level pot at the output. Additionally, the presence pot connects to an 82n cap / 1k resistor to ground and the feedback loop of the non-inverting op amp gain stage.

If you’re looking for a passive, first-order low pass filter, use a series cap and a pot configured as a variable resistor to ground. Keep in mind that you might need a gain recovery stage depending on what else is going on in the circuit.

EDIT: I didn’t notice you had said boost as well. Anything that involves boosting frequencies will have to be active. That might be happening with this circuit, but I’m not exactly sure how the presence control is interacting with the gain stage. In any case, a passive R-C network won’t get you what you’re looking for here.

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