Brightening up a Tone Pump

[inertian]

So this is where everyone went?! Glad to finally find this place!

Brought this up on the old forum, don't recall the specfics of the responses.

I have an old Tone Pump (three knob, black box, yellow labels, pictures below) whose Tone control doesn't do much. Not sure if its a bad pot, shot component, or what. The pedal has a great sound except it is too compressed, muddy, indistinct, not bright, etc., unless the Tone control is turned all the way up. In fact, the Tone control only seems to have any effect in the last quarter of its range. If I could add some treble to the range of the Tone control it would be perfect. I have played with the internal trim pot (Bass control I believe), doesn't fix the problem. Every Barber pedal I've played has excellent articulation at all settings - this one does not.

Meanwhile, I swapped out the stock op amp (the lettering on it is illegible) and installed an old Fairchild MC4558CP I had laying around. Surprisingly, the pedal now sounds warmer, rounder, sweeter and more tube-like, with lotsa crunch on tap and no harshness. The Tone control is still not full range, but I can cut it back one quarter to half way and still get good articulation. Could I have had a bad chip?

All suggestions welcome.

[David Barber]

You could clip the diodes on the PCB (one in each direction), and insert a diode string (2 series 1n4148 in each direction),across the outside legs of the gain pot. Back off on the bass pot a little get some clarity. I can't remember what the small value cap is in the feedback loop, 47p?

[inertian]

Thanks for the detailed response.

I was hoping for something simple, like decrease the value of a tone section cap or resistor. Don't want to change the sound of the overdrive, just want to be able to "take the blanket off" the the Tone control so it has a usable range.