M800 - Hum

[seangarland123]

Hello - I’ve just finished the M800 pedal, and am experiencing hum when engaged.

I get a clean signal when bypassed, LED comes on when engaged, but no guitar signal and just a loud hum. I’m thinking maybe a ground issue, as when I touch the top of the Q1 transistor the hum is much louder.

 

[KR Sound]

Make sure all of your transistors are fully seated in those sockets! Sometimes it’s hard to tell, especially with 6 of them.

 

[seangarland123]

Make sure all of your transistors are fully seated in those sockets! Sometimes it’s hard to tell, especially with 6 of them.

Thanks. I checked that, and was able to bias all of them (except Q4) to around 4.5v. Still just hum.

When I touch the pots on the top side (the posts), it definitely changes the hum as well.

 

[seangarland123]

Did a little debugging. Reflowed some joints, and am able to get some sounds through, but still lots of hum. Will keep working, but open to any suggestions on areas to focus on.

 

[fig]

Have you gone through the biasing?

Well...read it through first Fig...sorry

 

[Laundryroom David]

Where’d you get your J201s?

 

[seangarland123]

Where’d you get your J201s?

From GuitarPCB. Used some in another build and they worked.

 

[seangarland123]

So I went through and removed all the sockets and soldered the J201’s directly to the board. Eliminated the hum, but also eliminated any sound whatsoever. I’m trying to get voltages on the J201’s, and not having any luck, so I’m wondering if I fried something when removing the sockets.

I’ll try an audio probe later tonight, although that’ll be a fishing expedition for me.

 

[Laundryroom David]

Did a little debugging. Reflowed some joints, and am able to get some sounds through, but still lots of hum. Will keep working, but open to any suggestions on areas to focus on.

Could you post some pics of the other side of the board? Maybe fresh eyes might spot something.