Building the Christine oscillating fuzz PCB

[Taylor]

Hum could be a couple things: a lot of times a hum has to do with bad grounding. Make sure the ground lug from your power jack, the sleeves of the 1/4" jacks, and the G pad on the PCB all connect to each other at a central point. Make sure that the enclosure itself is grounded (sometimes with powder coated boxes, the powder coating on the inside keeps the 1/4" jacks from grounding the enclosure). Also, any high gain distortion will amplify hum if it's coming from your guitar (e.g. single coils).

Now, feedback, yes that's normal. This is a crazy feedbacking oscillating weirdo fuzz.

[telebiker]

Trying to build this (my first build). The LED is working, but instead of sound there is only noise. Volume pot is reducing the noise level.

Going to disassemble this and debug where the problem is. I know that the design is not the best. Have to learn a lot of things.

[Taylor]

I would start by making an audio probe and seeing if your guitar signal is getting to the In on the PCB, just to eliminate issues with the bypass board wiring. This circuit will oscillate and making all kinds of noise depending on the settings of the power and OSC pots, but especially if there is no input. Also make sure all your ground points from your jacks and both PCBs are connected together.

[telebiker]

I have built an audioprobe. The thing is that some points have audio signal, some not. I have recorded a video where I'm testing all the contacts:

Unfortunately, I have not figured out where the problem could be. Would be grateful for any ideas.

[patrick398]

I have built an audioprobe. The thing is that some points have audio signal, some not. I have recorded a video where I'm testing all the contacts:

https://www.youtube.com/watch?v=VoCZTxqnzMc

Unfortunately, I have not figured out where the problem could be. Would be grateful for any ideas.

There's not much sense in just probing randomly around the board, you need to get the schematic and follow where the signal enters and travels through the board. In the video it sounds like you've got no clean signal on the board input. Do you have a bypass switch wired up? I'd recommend wiring input and output jacks direct to the board for now, confirm the effect is working and then tackle the true bypass wiring.

[telebiker]

There's not much sense in just probing randomly around the board, you need to get the schematic and follow where the signal enters and travels through the board. In the video it sounds like you've got no clean signal on the board input. Do you have a bypass switch wired up? I'd recommend wiring input and output jacks direct to the board for now, confirm the effect is working and then tackle the true bypass wiring.

I agree. I'm using an "Effect tester" PCB (https://www.delykpcb.com/product/effects-tester-mk-ii-pcb/) to debug the issue. As stated in the manual, I have connected 4 wires (9V, in, out, GND) and switched 3pdt which this Effect tester board has.

>  In the video it sounds like you've got no clean signal on the board input.

Does this mean that I should hear something while touching the board input with an audioprobe?

Also, am I right that "power starve" part from the schematics is not used in the pcb?

[Taylor]

Yes, you should hear your clean signal at the board input.

The power starve part is included on the PCB. It's the top left pot on the board. Rather than working on the power input pin of the chip, it inserts a variable resistance between the chip's ground pin and actual ground.

[telebiker]

If I hear distorted signal on the board input, what this could mean?

[telebiker]

It turned out that there was a mistake: I soldered one electrolitic capacitor wrong swapping polarity. I replaced it, soldered properly, and the circuit started to work as expected.

That would be interesting though to find out how it can be possible to investigate such issues with audioprobe? It gave me some weird results. What should I expect soldering the circuit in a wrong way? 

Tried the effect on a bass, sounds pretty interesting. Will post some pictures later.

[Taylor]

This particular circuit is probably more difficult to troubleshoot that way, because by design it's so chaotic and depends on the impedance of the source feeding it, etc. But in general, audio probing is useful for narrowing down the area where the issue lies. You can probe at the output of each active stage (opamp, transistor, or in this case inverter) to find where the signal isn't getting through.

[telebiker]

Thanks everyone for helping with the build. My first pedal with a lot of errors during making.

[soggybag]

What does that lower oscillator section do in this circuit?