Debugging Rullywow Queen of Tone (KoT clone)

[eskimoquinn]

Hey I am having some trouble figuring out why the second side of my KoT clone is emitting white noise. Side one works exactly as expected. But side two emits white noise any time it is engaged. What is strange is that when I was using an audio debugger, I could hear the white noise at the 3pdt switch. I have uploaded a video of what I mean, any suggestions?

https://www.youtube.com/watch?v=2rG35E7qBoo

Here is the schematic: https://www.rullywow.com/wp-content/uploads/2018/02/Queen-of-Bone-v2-Build-Doc-REVISED-v2.pdf

Things I have already done:
Switched the IC chip to the other side. It works fine.
Audio probed to find the start of the problem.
Checked the chargepump, same results with a different charge pump.

[eskimoquinn]

Ok after some sleep, re did my audio probe and R15 does not have the hiss. It appears after IC 2. Since I socketed the IC chip, I replaced that chip with another 4558 chip and the result is the same.

[eskimoquinn]

Went through all the components and checked all the solders, nothing bad to my eyes. Uploading a pic in case anyone sees something I missed.

[blackieNYC]

This hiss - is it in addition to your guitar sound or along with the guitar?  If there is no guitar audio, there may be a gap in the audio path that turns the op amp into a noisemaker.

[eskimoquinn]

Well I have removed the hiss!

It seems like perhaps the socket is not seated properly or something. Because pressing down on the op amp removed it. It occasionally comes back but pressing it back down removes it. So clearly something is not seated properly. I am going to replace that socket.

[eskimoquinn]

This hiss - is it in addition to your guitar sound or along with the guitar?  If there is no guitar audio, there may be a gap in the audio path that turns the op amp into a noisemaker.

The hiss is there whether I play or not. But when I play, its mostly bass frequencies that make it through and its a faint signal.

[ElectricDruid]

Well I have removed the hiss!

It seems like perhaps the socket is not seated properly or something. Because pressing down on the op amp removed it. It occasionally comes back but pressing it back down removes it. So clearly something is not seated properly. I am going to replace that socket.

Before you try to remove a IC socket from a manufacturer PCB, I'd try resoldering the joints on that socket. A bad joint might make a decent contact when you press on it, and then go open when you let go. Resoldering is a lot easier than trying to pry the socket out, so it's worth a shot first.

Alternatively, pull the op-amp out of the socket and put it back in. Check the legs are straight and none got bend under the chip. Do it a few times. On sockets that have been around a while, you sometimes get a layer of oxidisation that prevents a good contact being made, and re-inserting the chip a few times often helps scrape it off.

Good luck!

HTH,
Tom