Dual supply boost with ground loop hum issue

Locrian99

Locrian99

Well-known member
So I started working on this project a while back. And I’m now on my 3rd pcb revision all with the same problem so I’m leaning towards it not being a layout issue. Wondering if anyone sees an issue with my schematic here. Basically its just the frequency interchanger I wanted to run with a dual supply.

Carbon-Boost-page-0001.jpg

I can post my actual layout later as I’m not at my computer. The hum appears at c5, and you can completely filter it out with the hpf pot.

If anyone sees a glaring issue id’d appreciate it.
 
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Bummer that my suggestions didn't fix it. Another probably really easy thing to try in terms of ruling things out -- what happens if you power it with a 9V battery (or depending on the state of your workbench, a fancy lab supply?) That can help narrow down whether or not you're fighting against injected hum from your power supply vs something that your charge pump is doing.

Another easy test, is with the pedal at maximum-noisy settings, what happens when you short the input to ground right at the jack - does it stay noisy? (That helps to rule out where the noise is coming from - you might not hear much hum leaving IC1 but it could be amplified by the next stage). This might help you figure out if you've got some noisy stuff routed right next to your inputs (which are the most susceptible places for noise pickups, since they're high impedance and everything after that gets amplified by the gain stages).

Also, the fact that it starts at 52hz rather than 60hz is awfully weird but maybe is a measurement issue, I guess a scope could also get an accurate measurement of that.

Your ground plane does look awfully cut up, and it might be that the shortest path for ~everything all goes through something with a lot of noise. That's harder to bench test, though.
 
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z2amiller said:
Bummer that my suggestions didn't fix it. Another probably really easy thing to try in terms of ruling things out -- what happens if you power it with a 9V battery (or depending on the state of your workbench, a fancy lab supply?) That can help narrow down whether or not you're fighting against injected hum from your power supply vs something that your charge pump is doing.

Another easy test, is with the pedal at maximum-noisy settings, what happens when you short the input to ground right at the jack - does it stay noisy? (That helps to rule out where the noise is coming from - you might not hear much hum leaving IC1 but it could be amplified by the next stage). This might help you figure out if you've got some noisy stuff routed right next to your inputs (which are the most susceptible places for noise pickups, since they're high impedance and everything after that gets amplified by the gain stages).

Also, the fact that it starts at 52hz rather than 60hz is awfully weird but maybe is a measurement issue, I guess a scope could also get an accurate measurement of that.

Your ground plane does look awfully cut up, and it might be that the shortest path for ~everything all goes through something with a lot of noise. That's harder to bench test, though.
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This is the start of my weekend so tomorrow I will try and get the scope out which I'm not the greatest with but I can usually manage to get what I need done done. I'll try the try shorting the ij to ground as well tomorrow probably do that through the scope as well. Last night I feared for my speaker a bit when I didn't realize how loud I had it and that hum came through lol. Not to mention the wife yelling from downstairs wtf was that

Edit: maybe this is my sign to switch to kicad and just make this an easy 4 layer board, that should be a cake walk to get the perfect ground plane and keep the ins and outs well seperated.
 
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