grounding in independent volume controls

[danw]

This may or may not be the same problem that a guy had on this forum a week or so ago, but I checked that thread and didn't see where he resolved it.

I have my guitar wired for independent volume controls, that is, on each volume pot, the jack is wired to the leftmost lug and the pickup is wired to the center lug. The way I understand it, this makes it so the pickup is sent to ground instead of the output jack when both volumes are all the way down. But in that case is the jack totally ungrounded? When I turn down both pots all the way, I get a LOT of hum coming in, which gets much worse if I let go of the strings. Is that a flaw in this design, or do I have a different wiring problem?

 

[ggunn]

This may or may not be the same problem that a guy had on this forum a week or so ago, but I checked that thread and didn't see where he resolved it.

I have my guitar wired for independent volume controls, that is, on each volume pot, the jack is wired to the leftmost lug and the pickup is wired to the center lug. The way I understand it, this makes it so the pickup is sent to ground instead of the output jack when both volumes are all the way down. But in that case is the jack totally ungrounded? When I turn down both pots all the way, I get a LOT of hum coming in, which gets much worse if I let go of the strings. Is that a flaw in this design, or do I have a different wiring problem?

I'd try connecting the hot pin of the jack to the wiper (middle lug) through the pickup switch, and pickups and ground to the other two lugs. If you don't go through a switch, then turning down either pot will ground the output and shut off all the signal, though. That's the way a Les Paul is wired.

 

[Whale Bone]

Is the remaining lug on each of the volume pots connected to ground? It should be, regardless of the wiring - master vol setup or independent vol, like you have. It's usually to the chassis of the pot which is then connected to ground. In your case, that way the output jack always sees a complete circuit to ground: at 10 - the pickup; at 0 - the volume pot; in between - a combination of the two.

Proper shielding in the control cavity can't hurt either, though with volume down even with bad shielding, I haven't had the problem you describe.

 

[Light]

I'd try connecting the hot pin of the jack to the wiper (middle lug) through the pickup switch, and pickups and ground to the other two lugs. If you don't go through a switch, then turning down either pot will ground the output and shut off all the signal, though. That's the way a Les Paul is wired.

Except then they are not independent, but are instead interdependent. I.E., if you turn down one volume control when both pickups are on, they both get attenuated. Having the pickup to the whipper (the center lug) gives you independence between the two pickups, so you can blend them more precisely. This is how J Basses are wired.


To answer the original question, no, you should not be getting an unusual amount of noise. The pot itself provides are path to ground, albeit with an awful lot of resistance.



Light

"Cowards can never be moral."
M.K. Gandhi

 

[danw]

Thanks, guys. Let me see if I have this straight. The difference between the two setups, with both volumes at zero, is that in the standard paul wiring, the jack should be connected to ground with no resistance, and in the jazz bass setup, the connection is there, but through the full resistance of the pot(s).

I think that's what I've got. Checking the DC resistance between the points on the jack, I get 11 or 12 Kohm with one or the other volumes all the way up (the pickups) and around 250 with both all the way down, which I presume to be two 500k resistors in parallel. What I'm wondering is if so much resistance is acting like a bad connection. That is, can my amp tell the difference between 250K and infinity?

It's only really bothersome on the highest gain setting. Inside the cavity, the resistance between any two ground points I checked appears to be less than 1 ohm, like around 0.3. Yes, the third lug on both volume pots is connected to ground. The cavity itself is unshielded, but I used shielded wire (the push-back stuff from stew-mac) for the runs from the pots to the hot wire on the jack. I didn't use the shielded stuff for connections to ground, because the shield is going to ground anyway, and that seemed redundant to me. But maybe I'm missing a subtlety here.

 

[Whale Bone]

What you describe sounds right. Have you grounded the pot casings/chassises? The third lug is usually connected to the casing. They would also likely be grounded from the shielding if you had it, but since you don't, the more direct and dependable method would be preferred. My Jazz would be the same as yours with vol at 0 - two 500K pots in parallel, and my is totally silent with vol down in even the worst enviroments.

I've never played an instrument without the pot casings grounded, and I play bass (super-high gain situations rare for me), so I'm not sure if that would be enough to cause the problem, but it couldn't hurt to make the connection, if it's not already.

I have benefitted from shielding my basses better than Fender and Gibson did originally, so you might try that as well.