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Tone pot causes volume drop on Mustang PJ - need help please
- Thread starter cattrax
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- jazz pickup mustang tone volume
Thanks for the info! I remember your posts on the Telecaster rewiring you had done. Looks beautiful.Two options spring to mind:
- The coil in the Jazz pickup is broken internally. Tone controls act as volume controls on pickups with broken coils.
- The tone control appears to roll off the volume, but isn't. The capacitor in those PJ Mustangs is 0.1 uF, which is quite a high capacitance value for the job required. I've changed out the caps in both my Mustangs to 0.022 uF, and I think it is an improvement. I also rewired both of mine using Telecaster wiring schemes. From memory this reverses the order of the wires in the volume pot, where and how the tone control is wired and configured in the circuit.
The stock wiring in the PJ Mustangs isn't all that good. One of mine came from the factory with the ground wire unsoldered at the 3-way switch. It was simply wrapped through the eyelet on the switch and allowed to flop around.
This was my revised wiring scheme for one of my Mustangs:
Well, I disconnected the jazz pup's white (hot) wire at the switch. Measuring the resistance between the hot and ground terminals on the pickup, I get the OL reading.
This means the pickup is dead, right?Could I have done something to kill it while I was shielding the cavities or swapping the switch out? It worked before I did the mods, and doesn't work now. What could have caused this?
BTW, I am learning so much through this process. Thank you all for the help!
The only thing I can''t see in the OP's photos is where the volume potmis actually grounded. Yeah, the lug is soldered to the can,mbut nothing else, unlike the later shots of the other bass where both pot cans and one lug are clearly alltied to ground,along with the sleeve of the output jack. If that connection is there, it is hidden well . . .
- Tim
- Tim
You are correct! Thanks, I hadn't noticed that. I like @Axstar's wiring scheme and plan to rewire everything in my bass, but my most immediate concern is what did I do to ruin the pickup? -- so I don't make that mistake again.
Pull the pickup completely out of the bass and measure it again. Visually check all the solder joints on the attached pickup wires. Something could have gotten nicked or broken accidentally during all the movement of doing the shielding work. Carefully retouch the solder joints on the pickup.
Re: the volume pot ground - the metal control plate is probably acting as the ground for the volume pot. In the OP's original photo, you can see that there is no wire attached to the sleeve connection of the output jack. Not the best, most bulletproof way to do things, but probably a cost-cutting measure...("Yep, we saved 50 cents not putting a common ground wire in that control cavity. Maybe we will get a production efficiency award")
It should still work, but when you re-wire, you might want to run a common ground from the switch thru to the pots and the output jack anyway. Belt and suspenders, and all that... The sleeve of the output jack is always ground central.
Re: the volume pot ground - the metal control plate is probably acting as the ground for the volume pot. In the OP's original photo, you can see that there is no wire attached to the sleeve connection of the output jack. Not the best, most bulletproof way to do things, but probably a cost-cutting measure...("Yep, we saved 50 cents not putting a common ground wire in that control cavity. Maybe we will get a production efficiency award")
It should still work, but when you re-wire, you might want to run a common ground from the switch thru to the pots and the output jack anyway. Belt and suspenders, and all that... The sleeve of the output jack is always ground central.
Pull the pickup completely out of the bass and measure it again. Visually check all the solder joints on the attached pickup wires. Something could have gotten nicked or broken accidentally during all the movement of doing the shielding work. Carefully retouch the solder joints on the pickup.
Re: the volume pot ground - the metal control plate is probably acting as the ground for the volume pot. In the OP's original photo, you can see that there is no wire attached to the sleeve connection of the output jack. Not the best, most bulletproof way to do things, but probably a cost-cutting measure...("Yep, we saved 50 cents not putting a common ground wire in that control cavity. Maybe we will get a production efficiency award")
It should still work, but when you re-wire, you might want to run a common ground from the switch thru to the pots and the output jack anyway. Belt and suspenders, and all that... The sleeve of the output jack is always ground central.
Thank you! I will do that tonight and report back. I appreciate your help.
My personal theory is that if it's worth the trouble to shield the pickup & control cavities of a bass, it's worth the extra effort to shield the hole(s) that the pickup leads travel through. I used a bit of 1/4" copper tubing, like what they would use to hook up the water dispenser on a refrigerator door. I cut it to length, removed any sharp edges (but used heat-shrink over the pickup leads to protect them anyway, just in case), then soldered it to the copper tape shielding. It's pretty bullet-proof. It has the added benefit of ensuring the copper lining of the pickup route actually acts as shielding.
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Almost all of my guitars are Mustangs (the 6-string guitar), and I've rewired most of them, and I don't bother with a common ground wire. I mean, really, what's the point? It's just one more wire for a connection that already exists. Control plates are nice like that. You can clamp down crazy tight on them and things don't move.Pull the pickup completely out of the bass and measure it again. Visually check all the solder joints on the attached pickup wires. Something could have gotten nicked or broken accidentally during all the movement of doing the shielding work. Carefully retouch the solder joints on the pickup.
Re: the volume pot ground - the metal control plate is probably acting as the ground for the volume pot. In the OP's original photo, you can see that there is no wire attached to the sleeve connection of the output jack. Not the best, most bulletproof way to do things, but probably a cost-cutting measure...("Yep, we saved 50 cents not putting a common ground wire in that control cavity. Maybe we will get a production efficiency award")
It should still work, but when you re-wire, you might want to run a common ground from the switch thru to the pots and the output jack anyway. Belt and suspenders, and all that... The sleeve of the output jack is always ground central.
Everybody likes to mention this crazy theory about how one day things could loosen and you might lose the ground, but in practice, it just doesn't really happen, and I've seen soldered wires get broken off way more often than a pot that became so loose that it was no longer physically grounded.
You assume that the pot can is electrically connected to the mounting nut. That isn't always true . . . sometimes the face is phenolic (an insulator) and the tabs on the can that attach the two don't necessarily make the connection. Myself, I'll always run a lead to the pot terminal . . . easy to do, small, tidy, and one less thing to worry about.
anyway yeah, a bright thin J pickup that gets no resistance reading and in circuit gets turned off by the tone control being turned down means the pickup has a broken coil wire.
it's only making sound in the first place because of capacitance across the broken coil wire.
it's only making sound in the first place because of capacitance across the broken coil wire.
Me too, but I split a plastic straw and twist it to decrease the diameter to size it for the channel. I then wrap it in copper tape, cut it a little longer than the channel and use solder to tack either end to the shielding.
Pots with an insulated body are usually sold with a grounding tab because they literally can’t be grounded to their body, so given that that’s only held in place by physical clamping force, so I don’t know what point that makes.
Whatever . . . .as usual, the initial point was lost and the irrelevant trivia beat to death instead. That point being that there did not appear to be a ground to the volume pot visible in the pictures, and (god forbid), it might actually have been a factor in the problem.
Pull the pickup completely out of the bass and measure it again. Visually check all the solder joints on the attached pickup wires. Something could have gotten nicked or broken accidentally during all the movement of doing the shielding work. Carefully retouch the solder joints on the pickup.
Re: the volume pot ground - the metal control plate is probably acting as the ground for the volume pot. In the OP's original photo, you can see that there is no wire attached to the sleeve connection of the output jack. Not the best, most bulletproof way to do things, but probably a cost-cutting measure...("Yep, we saved 50 cents not putting a common ground wire in that control cavity. Maybe we will get a production efficiency award")
It should still work, but when you re-wire, you might want to run a common ground from the switch thru to the pots and the output jack anyway. Belt and suspenders, and all that... The sleeve of the output jack is always ground central.
I pulled the pickup out completely and still get the OL display on my multimeter between the hot and ground terminals. I guess that confirms it is dead. When I get a new pickup to install, I will check and re-solder all connections throughout. Thanks!
Makes perfect sense! I didn't have any copper tubing, so I used a straw and copper tape. Turned out great! Thanks for the tips.
In the harnesses I wire, such as the one I showed earlier, I always include a ground wire. In the case of the harness I posted, I use the legs of thru-hole components as ground wires. I do this because it adds a bit of mechanical security as it locks the components in place. I would hate to be at a gig (and it would happen on a gig) to turn the volume control and suddenly ground out the 'hot' lugs on the volume. Instant no bass.
I also do it as I like to see the ground wires when I'm wiring up stuff. That way I don't forget anything else.
Totally overkill, total over-engineering, but it puts my mind at ease.
I know what you're saying, but I just also believe that I don't need to worry about a problem where the components become physically loose to the point of shorting out, which would have to literally be falling into the guitar/bass because even if the hex nut becomes slightly loose, it's a world of difference between that and actually losing connection to the plate. For instance, in your control plate, if your pots ever got loose, things aren't as bulletproof as it seems because I've seen ground wires (esp. solid core) get detached from the physical action of pots turning when they weren't clamped tight. Really, we all need to keep our components tight and part of our regular maintenance should be checking to make sure all the components are tight.
I build in safety valves, too. I just prioritize different ones. I wire everything with slack and use stranded core wire, not solid core as you have. I do this because if one pot becomes loose or needs to be changed out, I don't want the wires to be under tension, since this makes it likely for connections to break when they are physically disturbed. That said, there's nothing wrong with your wiring. I'm just saying we all have different philosophies for our wiring based on what we think we need to be prepared for. I especially likes the bits of heat shrink. I do this pretty often on output jacks in shielded cavities since that's the easiest way to lose all output, but it's a good idea to do that on the outer lugs of volume/tone knobs, too, since they can touch a shielded cavity, so props for that.
This was my revised wiring scheme for one of my Mustangs:
Totally overkill, total over-engineering, but it puts my mind at ease.
I finally received my new pickups and am ready to re-wire everything. @Axstar, it's hard to see in the pics of your extremely neat wiring... is the capacitor soldered to lug#1 or #2 (middle lug) of the tone pot? I noticed you also moved the jumper wire between the volume and tone pots to lug#1 on the tone pot. Mine is originally wired to the middle lug on the tone pot. Should I move it to lug #1?
