Ground/Pickup Question

[Sonlen60]

Hi everyone,

I’ve spent many hours lurking on TB but this is my first post. I have a cheap P-Bass copy that I got to learn how to install pickups, solder, etc. I have spent a long time searching the forums and learned a lot but haven’t found a clear answer to my questions yet.

I have installed new pots, both 250k with an orange tone cap. I also installed DiMarzio Model P pickups. I have everything wired, soldered, and shielded but I have two remaining questions:

1) is a ground wire from the bridge to the volume pot enough? I have read much on the subject and seems like everyone does it differently. Initially I had a lot of buzzing that was greatly reduced with the shielding, but still some buzz and just wondering if it s a grounding issue. Buzz totally stops when I touch the bridge, pots, etc.

2) when I move my fingers over the pickups I get a lot of loud buzzing, and it gets even louder when I touch the pole pieces. Do I need to ground the pickups somehow or is this a different problem?

I attached a pic of my wiring in case it helps. Please ignore the horrific soldering job, it was my first time and it didn’t go well
Hoping to not redo any of it if I don’t have to, everything works the way it’s supposed to as far as I can tell so I’m hoping I can leave it as is

 

[dwizum]

1) is a ground wire from the bridge to the volume pot enough?

That's an interesting phrasing for a question about grounding, but I think I see what you're stuck on.

Think of the ground wires in your bass like the drain plumbing in your house. Every plumbing fixture needs a drain to the sewer line that leaves your house. It's that simple for your bass, too. Every electronic component needs a ground connection to the jack.

Connecting the bridge to the volume pot - and ONLY connecting those two things - would be like connecting your bathroom sink's drain to your kitchen sink's drain. The waste water has nowhere to go. You need a connection to the outside world so it can all drain! If you connect the bridge and volume pot together, you also need a connection to the "outside world" via the ground lug on your jack.

You already have that though, since - looking at your photo - the volume pot ground is connected to the tone pot ground, which is connected to the ground lug on the jack.

It does look like you've done a thorough job of shielding, but it doesn't seem like your shielding is well connected to ground. Back to the plumbing analogy - if the shielding is your tub, you've got a thin little plugged line running to your sewer, when you want a nice big clear line! For copper tape, I like to strip a length of wire and wrap it around a small screw, then drive the screw into the bass right through the shielding tape - then cover the screw and length of wire with another piece of tape. This gives a solid mechanical connection that's held tight by both the screw and the tape. Then run the other end of the wire to one of your ground points. Make sure the shielding on the pickguard is well grounded too. Your complaint of the hum going away when you touch the bridge is a classic indication that your bridge is grounded OK, but your shielding is either absent or not well grounded. When you touch the (well grounded) bridge, your body basically becomes part of the shielding (your body is a large, mostly conductive object that's now attached to ground). What you need to do is get the shielding on the bass to play the role your body plays.

The other issue I see in your photo is slop in your pickup leads. That ball of wire you've got there is like a giant antenna for noise. I know people get crazy about pickup lead length, and they like to keep the wires long "just in case" or because it sounds good in a classifieds add to say that the wires are long, but that's not really good practice from a noise perspective. Any length besides what it takes to get to your controls is just going to be a noise magnet. Make the wires just long enough that you can handle the parts as needed (i.e. you don't want them literally TIGHT between the pickup and the pot, or else you won't be able to service things easily). The two wires that connect the two halves of the P pickup don't need to be any longer than to get between the two halves. And - for bonus points - the ground and signal wire that run from the pickup to the volume pot (green and red in your case) can be twisted around each other, which lets the ground wire act as a shield for the signal wire.

Before you touch the pickup wiring, it may make sense to check the wire colors for the 4 wires from your P pickup. It's hard to tell from looking at your photo if you've got the wires run correctly and reversing one or both of the pickup halves could cause noise problems too.

Cleaning up the wiring and getting a better ground on the shield should help your noise problem though. Make those changes, give it a play, and let us know how it sounds.

 

[Sonlen60]

That's an interesting phrasing for a question about grounding, but I think I see what you're stuck on.

Think of the ground wires in your bass like the drain plumbing in your house. Every plumbing fixture needs a drain to the sewer line that leaves your house. It's that simple for your bass, too. Every electronic component needs a ground connection to the jack.

Connecting the bridge to the volume pot - and ONLY connecting those two things - would be like connecting your bathroom sink's drain to your kitchen sink's drain. The waste water has nowhere to go. You need a connection to the outside world so it can all drain! If you connect the bridge and volume pot together, you also need a connection to the "outside world" via the ground lug on your jack.

You already have that though, since - looking at your photo - the volume pot ground is connected to the tone pot ground, which is connected to the ground lug on the jack.

It does look like you've done a thorough job of shielding, but it doesn't seem like your shielding is well connected to ground. Back to the plumbing analogy - if the shielding is your tub, you've got a thin little plugged line running to your sewer, when you want a nice big clear line! For copper tape, I like to strip a length of wire and wrap it around a small screw, then drive the screw into the bass right through the shielding tape - then cover the screw and length of wire with another piece of tape. This gives a solid mechanical connection that's held tight by both the screw and the tape. Then run the other end of the wire to one of your ground points. Make sure the shielding on the pickguard is well grounded too. Your complaint of the hum going away when you touch the bridge is a classic indication that your bridge is grounded OK, but your shielding is either absent or not well grounded. When you touch the (well grounded) bridge, your body basically becomes part of the shielding (your body is a large, mostly conductive object that's now attached to ground). What you need to do is get the shielding on the bass to play the role your body plays.

The other issue I see in your photo is slop in your pickup leads. That ball of wire you've got there is like a giant antenna for noise. I know people get crazy about pickup lead length, and they like to keep the wires long "just in case" or because it sounds good in a classifieds add to say that the wires are long, but that's not really good practice from a noise perspective. Any length besides what it takes to get to your controls is just going to be a noise magnet. Make the wires just long enough that you can handle the parts as needed (i.e. you don't want them literally TIGHT between the pickup and the pot, or else you won't be able to service things easily). The two wires that connect the two halves of the P pickup don't need to be any longer than to get between the two halves. And - for bonus points - the ground and signal wire that run from the pickup to the volume pot (green and red in your case) can be twisted around each other, which lets the ground wire act as a shield for the signal wire.

Before you touch the pickup wiring, it may make sense to check the wire colors for the 4 wires from your P pickup. It's hard to tell from looking at your photo if you've got the wires run correctly and reversing one or both of the pickup halves could cause noise problems too.

Cleaning up the wiring and getting a better ground on the shield should help your noise problem though. Make those changes, give it a play, and let us know how it sounds.

Thanks so much! That’s much more helpful and simple than anything I’ve read. I will work on those changes today! Thanks for the tip on the pickup wires too, I know I wired them correctly because I followed DiMarzio’s instructions, but I was wondering about the wire length. I’ll trim them and clean up the cavity.
Any ideas on the pickup buzz? I know single coils will naturally hum, but this is definitely more of a buzz and gets worse when I touch the pickups or get my finger near them. Will that be fixed with the changes you suggested or is that a different issue?

 

[pit lenz]

As you are in the process of resoldering your rig, I would suggest watching some soldering tutorials first. Sloppy soldering may look ok cause the wires are not falling off right away but quite often the inner structure of a sloppy (or „cold“) soldering blob may cause bad electrical connection from the start or further down the road. This may be a part of your ground issues as well. Here‘s a video where the guy talks a lot but gives good tips about what to consider.