Thinking about a modified Zoom PD-01 Power Drive

[Rodgre]

Hello all!

I have been using a Zoom PD-01 Power Drive on my pedalboard for many years. I use it as a solo boost and a clean enhancer. I never turn the GAIN control up at all. It's a unique pedal in that when GAIN is all the way counter-clockwise, it is a fantastic clean boost with EQ. As soon as you leave the "off" position of that pot, the whole tonality changes and it becomes a midrangey overdrive. I never use that sound and I get irritated sometimes when the knob gets jostled in the flight case or during a show and I start to wonder why my tone sounds so bad!

Anyway, looking at the schematic just now, it's looking like there is a buffer and an overdrive in parallel in the early stage of the pedal. The GAIN control sort of pans between them so when it is fully counter-clockwise, it is only getting signal from the buffer. Does this seem correct?

That being the case, if I were to build a smaller clone of this pedal but omit the lower overdrive circuit on the schematic, will it just be the clean boost that I want to use (with the EQ section)?




Thank you!

Roger

[11-90-an]

I think that the overdrive section still has some part in the boost, as when you turn the gain knob up there still is some "processed overdrive" signal present and if you build a solo boost circuit, you probably won't like it that much... (maybe)

Sooo... the easiest thing to do is actually find some way to stick that pot in place, like put some foam under to make it hard to turn...

[Rob Strand]

Anyway, looking at the schematic just now, it's looking like there is a buffer and an overdrive in parallel in the early stage of the pedal. The GAIN control sort of pans between them so when it is fully counter-clockwise, it is only getting signal from the buffer. Does this seem correct

That being the case, if I were to build a smaller clone of this pedal but omit the lower overdrive circuit on the schematic, will it just be the clean boost that I want to use (with the EQ section)?

?

Yes, once you go fully ccw on the gain it's only buffers.

I suspect there is another buffer to the left of the schematic.  Probably the other half of IC3.  Maybe with 470k  + 100n input and the 470k going to the Vref supply.

C29 and C37 provide a very small amount of high-pass filtering (~25Hz and 16Hz)

C36, R18, R14 might have a very small effect.  That detail would need to be checked.

If you wired the output of IC2 pin 7 directly to R4 and dumped C36 through to IC5 pin 7 you pretty much have it.  Presumably Q4 is to stop buzz getting into the clean path.   With the simple clean boost only set-up you *might* be able to ditch it.

[11-90-an]

Anyway, looking at the schematic just now, it's looking like there is a buffer and an overdrive in parallel in the early stage of the pedal. The GAIN control sort of pans between them so when it is fully counter-clockwise, it is only getting signal from the buffer. Does this seem correct

That being the case, if I were to build a smaller clone of this pedal but omit the lower overdrive circuit on the schematic, will it just be the clean boost that I want to use (with the EQ section)?

?

Yes, once you go fully ccw on the gain it's only buffers.

I suspect there is another buffer to the left of the schematic.  Probably the other half of IC3.  Maybe with 470k  + 100n input and the 470k going to the Vref supply.

C29 and C37 provide a very small amount of high-pass filtering (~25Hz and 16Hz)

C36, R18, R14 might have a very small effect.  That detail would need to be checked.

If you wired the output of IC2 pin 7 directly to R4 and dumped C36 through to IC5 pin 7 you pretty much have it.  Presumably Q4 is to stop buzz getting into the clean path.   With the simple clean boost only set-up you *might* be able to ditch it.

That R21 though... it limits the full turn of the gain pot to 16k... and the other gang of the gain pot works pretty much like again pot... surely there would be a reason of this... right?

[Rob Strand]

That R21 though... it limits the full turn of the gain pot to 16k... and the other gang of the gain pot works pretty much like again pot... surely there would be a reason of this... right?

That's usually done to tune the way the control behaves from one end to another, making it seem more natural.   Sometimes people tweak the 12 O clock setting to match some pre-conceived sound.