noise from volume pot after adding spc to blackouts

jeremy

jeremy

LoveMachineologist
Staff member
i have a hamer daytona which i love and a few years ago i put a set of blackout singles in there. they are great sounding pups and being able to put the two output levels on a switch is great for a little boost when you need it. but of course, i wasnt satisfied so found an old emg spc control to wire in and a push/pull 25k pot to keep the switchable output. got it all wired up and it works great! other than the fact that the volume control makes horrible noise when turning it. it works normally, reducing output as its turned down, but makes nasty popping noise when you turn it. not a dirty pot crackle, but something different. its only the volume control, the tone and spc both work fine with no noise. what the heck could be going on?
 
That's the sound of DC riding on the pot. You can probably measure it with a meter. Generally, it means there may be a bad cap in the circuit, or possibly, two incompatible circuits. It can be a tough one to figure out.

A low value cap on the input to the volume pot may fix it. Say, in the 1 to 10 uf range. At the minimum, it will verify that that's the problem.
 
Step one is a cap in series with the input of the pot. I'd probably try 1 uf first. That will verify the problem and may fix it altogether.
 
Jeremy: What order do you have everything connected? BO's > 5-way > SPC > Vol? Or something else?
 
with passives, i know what im doing so seldom ask other than to get other peoples perspectives for curiosity's sake. ive been n here since the late 90s and have been an admin since rodney handed me the keys forever ago so learned a lot over the years. actives... i can wire them but when something goes weird, i need people like artie to save me :D

its wired pups to 5 way to volume to spc. like this:

https://images.thomann.de/pics/prod/171889.pdf

im sure i have a 1uf cap downstairs some where. put it between the spc and the volume pot or ?
 
I'd put it between the 5-way and volume input. That will rule out, or confirm, the BO's putting out DC. If that doesn't work, then between the volume output and the SPC. The SPC might be back-feeding DC into the pot.

Edit: Here's one more thing to try. I assume you have a meter. Can you check to see if you have any DC voltage across the outside lugs of the volume pot. With the meter attached, roll the volume back and forth. If the voltage stays constant, it's probably coming from the pups. If it drops to zero, it's probably back feeding from the SPC. That will let you know where to put the cap.

The voltage should be tiny. Maybe just a few millivolts.

Edit 2: Also, move the 5-way through it's positions. The voltage may only be coming from one pup.
 
Last edited:
ok, cool. thank you! should i expect it to sound different or is that value is big enough it shouldnt effect anything. i totally have a tone boner to have the blackouts with a mid boost so hope i can get this workin.

everything was fine with the blackouts till i put the spc in
 
That value shouldn't affect anything. But if does, try 10 uf. Or just use 10 uf to start with. Step one would be to see if you can actually measure the DC. That will steer us better to the cap value.
 
ok. ill pull the (brand new :17: ) strings off this weekend and poke around and see what i find with a meter then put a cap in there and see what i get. i probably have a 10 uf cap so ill try that first

edit: yes, thats how its wired

thanks for your help with this!
 
And don't forget, if you're going to try to measure the voltage, make sure you've got a cable plugged in. ;)
 
And, if this started with the SPC control, I might start with the cap between the vol wiper and SPC. But again, an actual voltage measurement, with volume up, then down, would be better.
 
ill start with readings for sure. when i heard it, i thought aww crap something is leaking dc, even though i had no idea what that sounds like.

once i open it up i can check for dc on the pot, then put the cap in both places to see if it helps. dont need strings on it for any of that
 
jeremy said:
ill start with readings for sure. when i heard it, i thought aww crap something is leaking dc, even though i had no idea what that sounds like.

once i open it up i can check for dc on the pot, then put the cap in both places to see if it helps. dont need strings on it for any of that
Click to expand...

Just remember, (to make things easier), if the voltage drops to zero when you roll the volume down, then the cap should definitely go between vol pot and SPC. Or, you may even have a faulty SPC and maybe want to return it. If it's new. They shouldn't backfeed voltage.

P.S. When you aren't actually turning the pot, how does she sound?
 
everything sounds awesome when im not turning the pot. between the two switchable levels of output of the blackouts (at least for neck and bridge, middle is low output only since im using a p/p 25k pot) and the mid boost its everything i hoped.

the spc is old. the new ones have the quick connects which im sure i could make work, but ive had this one for years and its easier to work with wires
 
Yup. I like wires too. Now I'm GAS'ing for an SPC.

I wish Duncan would make more stuff like this. I have the ABC control for my bass, but haven't installed it yet.
 
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