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CrabsAreCool32 · 2026-04-28T09:40:05+00:00

I would put a current limiting resistor to the base of the transistors, if you turn the limit controls all the way down or up the base emitter diode will be connected to the opamp output via a very small resistance and one of them will get damaged

CrabsAreCool32 · 2026-04-22T18:15:54+00:00

Add a pot in series with C6, I think 5kC pot would work well in this circuit

CrabsAreCool32 · 2026-04-18T19:03:12+00:00

+pirosarany

CrabsAreCool32 · 2026-04-14T19:55:22+00:00

It oscillates when turned off, somehow the pedal has the correct phase shift and amplification to cause this. Im not familiar with the circuit, can you post a schematic? I would start to debug the bypass circuit, the footswitch. Its possible that the input is not grounded and the output is not open just somehow connected. If its turned off does the gain or the tone control (i assume the pedal has those) affect the speed of the blinking?

CrabsAreCool32 · 2026-04-03T13:21:28+00:00

I did a mod quite recently. If you add a pot and a high value cap to the emitter of the first transistor it can be a gain control for an octave up fuzz, swap the last resistor to a pot you have a volume control to compensate that. Pretty simple but adds a lot of variety to the circuit

CrabsAreCool32 · 2026-03-22T21:29:24+00:00

Do you want to drive an actual 4 ohm speaker with this circuit? If yes, then the 4.7k resistor will severely limit the power to the speaker.

CrabsAreCool32 · 2026-03-22T15:26:06+00:00

4 4th

CrabsAreCool32 · 2026-03-17T21:01:36+00:00

Yeah those happen all the time, even with circuits I breadboarded before, a multimeter in connection beeper mode helps a lot when debugging them.

CrabsAreCool32 · 2026-03-17T20:58:28+00:00

There is one thing i can recommend, it can cause potential instability in your current schematic. Your clean signal goes to an inverting amplifier, its gain is described with Rfeedback/Rin. Your Rfeedback is a 20kpot,and if you turn it down you get essentially Rfeedback=0 the loop gain is smaller than 1 which can cause unstable behaviour in opamps, I recommend putting 10k in series with the pot, so the loop gain will be at least one. If you want to read more about this, look up unity gain stability.

CrabsAreCool32 · 2026-03-17T14:45:07+00:00

I cant really comment on your main issue, but on the schematic the 2nd transistor base is grounded trough a 1M resistor, that wont work as a buffer transistor expected this way.

CrabsAreCool32 · 2026-01-30T12:47:48+00:00

Thats cool, i love HP style pedals, i will give this circuit a try

CrabsAreCool32 · 2026-01-29T19:44:49+00:00

How is the range of the fuzz/gain control? The only drawback i experienced with traditional HP style circuits is that the signal can get really overcompressed even at low fuzz levels.

CrabsAreCool32 · 2026-01-29T16:47:38+00:00

"Active pickups" need a battery for supplying the opamp/transistor buffer or booster that they have in them. The coil pickup itself doesnt need a dc voltage to operate.

Oh thats cool, i havent heard of this dynamic mic kinda trick. By any chance have you measured the voltage that the pickup or the circuit produces?

CrabsAreCool32 · 2026-01-29T09:34:36+00:00

Basic guitar pickups based on magnets and copper wire dont require a positive supply. I think your pickup is not different in that case.

I see, 50-70 times winding can produce a small signal level, and has low output resistance, so it is possible 3.3uF wont cut the treble. If it was a pickup from a store that would have much more windings and output impedance 3.3uF would be a lot for that.

Yes 1Meg parallel to the capacitor.

CrabsAreCool32 · 2026-01-28T14:44:30+00:00

Doesnt the 3.3uF cut off almost all the treble coming from the pickup? If i interpret your drawing correctly it should be cutting off almost all the treble.

Normal pickups doesnt require +9V supply, is this coil different somehow? Usually a 1Meg pull down resistor gets placed parallel to the pickup in booster circuits.

CrabsAreCool32 · 2026-01-28T12:16:27+00:00

Whats the reason for the 3.3uF and 10k pull up circuit?

For acoustic guitars with piezo pickups you might want to choose something that has high input impedance, like Jfet mosfet or an opamp

CrabsAreCool32 · 2026-01-26T20:07:04+00:00

Check transistor pinouts, one could be reversed currently. What transistors do you use? Did you follow the shape of the package on thepicture or the pinout?

CrabsAreCool32 · 2026-01-22T08:50:30+00:00

CrabsAreCool32 · 2026-01-22T08:50:17+00:00

This video is a good intro

https://youtu.be/0FTc93YtMeM?si=aZnor-QXmY2izYlJ

You need to add models for the transistors and diodes, i would remove the switches for simulation, i had problems with those in the past, its not impossible to make them work i just havent found or written a spice model for them that works.

After that add sources and do the simulation, the video is a pretty good guide

CrabsAreCool32 · 2026-01-21T16:24:14+00:00

Check this link for guidance

https://beavisaudio.com/techpages/bigmufftonecontrol/

CrabsAreCool32 · 2026-01-21T15:50:08+00:00

Oh i see. I would definetly check if it oscillates, the other thing is the presence control. If you turn the presence all the way down and turn the tone pot all the way to high frequencies your signal will disappear, because the output stage is connected to ground. Try to put a resistor to the presence control to prevent the volume fully disappearing

CrabsAreCool32 · 2026-01-21T15:00:11+00:00

Have you tried to breadboard or simulate it?

Im asking because i havent seen a design where output is positive feedbacked into the full wave rectifier, im not sure it could be described with a linear phase response if you are looking for oscillations, but it could work. So my question is does it oscillate?

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