Credits for the schematic to beavis audio research
My son is playing the electric guitar, and I wanted to build an effect pedal for him rather than buy one. Many schematics are using inductors and are threfore harder to build because of this but I found a schematic that doesn’t need an inductor, the Optochopto: Fun with the Colorsound Inductorless Wah.
To be able to use it I searched for a “blank” pedal with nothing but the potentiometer and in/out jacks. I got the Bespeco VM12 but there are a lot of other models out there. I needed one that had the 100KΩ potentiometer. The good thing about this pedal is that it has plenty of space inside to fit a PCB and it even has a screw hole that you can use to mount the board. Probably for other pedal models that have electronics in them. I screwed on the side a 9V battery holder with an on/off switch.
The schematic is pretty simple, with a single transistor, 2N5088. I didn’t have 2N5088 and I used a 2N2222 which is lower gain and higher noise; it works, but I plan to replace it with a 2N5088 on my next order. I’ll let you know the difference.
I tried the schematic on a perfboard and added the tremolo using the Trigger Schmitt and the optocoupler but got a lot of switching noise from the CMOS oscilator. I should have handled the decoupling of the power supply better and probably the ground design, but excluded the tremolo part eventually.
The components are not very demanding. You can use film capacitors.
The etched PCB didn’t look very well because I had a non-OEM toner in my printer and the ferric chloride went through it and attacked the copper.
You can find the the complete KiCAD project at the end of the post.
Here’s the board mounted in the pedal:
KiCAD project: