ground hum issue

[steve kudela]

Hey folks, I've got a strange issue that's got me and 3 other electronics guys stumped. I installed a popular name brand of pickups and preamp in a bass that I've built. A pbass pickup in neck position and a humbucker with a series, parallel, single coil switch in bridge position. Everything worked properly except for a ground hum. The hum was only emanating from the bridge pickup. If you touch the switch, the hum goes away. I spent some time checking things out to make sure that I had everything done properly, Even put a new s/p/sc in just to make sure that the issue wasn't from the switch. I did not ground the system to the bridge but grounded to the jack. I've done this a bunch of times with no issues..... So I spoke with an electronics guy and he recommended grounding to the bridge, so I ran a wire from the bridge to the grounding strap of the circuit. The active mode of the preamp stopped working, passive mode worked perfectly with no hum. So then I removed the bridge ground Thinking that it would work as before. It didn't. Active mode didn't work, very weak signal with a fair amount of static. passive worked fine with no noise. Have spoken with the maker of the preamp and pickups, tried a couple of things that he recommended to no avail. I know that this is not a great description but would anyone have an idea about what's going on? I don't think that it's an issue with the circuit or the pickups. I'm not an electronics guy, but have installed bunches of different circuits and pickups with no problems.Thanks much for your help.......SK

 

[LoveThatBass]

Are the control and pickup cavities shielded? If not I suggest you do this.
If shielded the shielding and bridge need to connect to the output jack's sleeve lug while pickup commons and preamp and battery common need to be connected to the Ring lug of the output jack

 

[dwizum]

Can you describe what the pickup maker had you try already?

Step one with any active circuit troubleshooting, especially when the bass works in passive mode: replace the battery with a brand new fresh battery. Step two: check the wiring around the active/passive switch. A bad solder joint or other problem can kill the active mode as you're describing.

I suspect that the "active mode doesn't work" problem is separate from the "bridge pickup is noisy" problem, so it probably makes sense to get active mode working first and then troubleshoot the noisy pickup.

And it may be helpful to clarify some of the terms you're using regarding grounding. You don't really ground the wiring "to" the bridge. What you're really doing is connecting the bridge to the ground wiring that should already be there in the bass. Regardless of whether or not there's a ground wire running to the bridge, the bass itself needs the internal controls and pickups connected to the ground terminal on the jack. When you add a ground wire to the bridge, and connect it to the grounding in the bass, you're creating a path from the strings to ground. That path means that when you touch the strings with your hand, your body is now grounded (through the instrument's wiring) and becomes part of the "shielding" around the bass.

 

[byacey]

Are the control and pickup cavities shielded? If not I suggest you do this.
If shielded the shielding and bridge need to connect to the output jack's sleeve lug while pickup commons and preamp and battery common need to be connected to the Ring lug of the output jack

This will kill the battery in awhile if the preamp ground is connected together with the battery negative lead, regardless of how the jack is wired.
I would connect all the grounds to the sleeve of the jack, and only the battery negative to the ring terminal.

 

[byacey]

As for the hum issue, it sounds like something isn't connected properly. Simply adding a ground to the bridge shouldn't affect the preamplified or passive operation aside from reducing the hum. If you can, find an actual electronics technician to look at it, rather than self professed "experts" with little to no actual credentials.

 

[byacey]

Accepted practice is to create a ground buss, a central grounding point. What I would do is solder a single piece of #14 solid wire joining the back of all the pot cases, and make all your ground connections to that wire.

 

[LoveThatBass]

This will kill the battery in awhile if the preamp ground is connected together with the battery negative lead, regardless of how the jack is wired.
I would connect all the grounds to the sleeve of the jack, and only the battery negative to the ring terminal.

Correct, my mistake

 

[steve kudela]

Are the control and pickup cavities shielded? If not I suggest you do this.
If shielded the shielding and bridge need to connect to the output jack's sleeve lug while pickup commons and preamp and battery common need to be connected to the Ring lug of the output jack

yes on both counts,....thank you for responding

 

[steve kudela]

Can you describe what the pickup maker had you try already?

Step one with any active circuit troubleshooting, especially when the bass works in passive mode: replace the battery with a brand new fresh battery. Step two: check the wiring around the active/passive switch. A bad solder joint or other problem can kill the active mode as you're describing.

I suspect that the "active mode doesn't work" problem is separate from the "bridge pickup is noisy" problem, so it probably makes sense to get active mode working first and then troubleshoot the noisy pickup.

And it may be helpful to clarify some of the terms you're using regarding grounding. You don't really ground the wiring "to" the bridge. What you're really doing is connecting the bridge to the ground wiring that should already be there in the bass. Regardless of whether or not there's a ground wire running to the bridge, the bass itself needs the internal controls and pickups connected to the ground terminal on the jack. When you add a ground wire to the bridge, and connect it to the grounding in the bass, you're creating a path from the strings to ground. That path means that when you touch the strings with your hand, your body is now grounded (through the instrument's wiring) and becomes part of the "shielding" around the bass.

yes, loosened, lifted, and replaced the pots one at a time with the bass plugged in. And went back through everything again to make sure of connections andmade sure no wires were trapped between the pots and the body. everything seemed ok.,.........replaced the batteries right off. I'll check the wiring on the a/p switch as you suggested. Thanks man

 

[steve kudela]

As for the hum issue, it sounds like something isn't connected properly. Simply adding a ground to the bridge shouldn't affect the preamplified or passive operation aside from reducing the hum. If you can, find an actual electronics technician to look at it, rather than self professed "experts" with little to no actual credentials.

Thank you Sir!

 

[byacey]

A technician will zero in on the problem right away, as it's a relatively simple circuit. It'll probably save you lots of time and anguish.

 

[MultiScaleMale]

^^^ Agreed. A tech will solve it quickly. This is a fairly simple circuit and is best solved in-person.