Tone pot grounding issue (pot at 0, no buzz)

[reluctant-builder]

I goofed somewhere, with my Jazzmaster wiring.

Recently, the bridge pickup started shorting out, so I opened her up to discover -- whoops -- the capacitor was so big, and its housing metallic, that it was being pushed into the terminal of the tone pot. So, I fixed that. Plugged her in and WOW, sounded great. No shorting out, serious balls to the sound ... but ... but ... hum. Even in the center position of the toggle, which takes advantage of the RWRP pickups and *should* be deathly quiet.

It's not, though. Not terribly loud, but there's the unmistakable sound of something ungrounded.

I've attached some, surely, bad shots of the pot ... it's wired up Gibson '50s style, with the cap spanning the volume pot's center lug to the tone pot's 10 lug. The tone pot's center lug goes to ground, and the 0 lug is just dangling out, doing nothing.

And here's the Jazzmaster wiring diagram, just for good measure:

 

[TroubledTreble]

Jack wired backwards? Are all pieces of shielding well connected to each other?  :icon_scratch:

 

[reluctant-builder]

Jack wired backwards? Are all pieces of shielding well connected to each other?  :icon_scratch:

Hey, Ken. No, the jack isn't wired backwards; I've got output ... and good output, at that. Everything sounds quite fine and works well, aside from that there is the notorious undercurrent of added, unwanted "grounding problem" hum.

If I roll the master tone pot to 0, the hum goes away. The guitar continues to work, the output is just as strong (albeit much muddier with the treble siphoned off) ... or maybe that's the tone pot on 10? And on 0 it's the problem?

I can't claim to know how the tone knob actually works (when it preserves treble (10?) versus leeching it (anything less than 10?), that is); I just copied the wiring scheme I have in both of my (quiet) Hagstroms, which each have '50s wiring. One of them came that way, stock, and the other I modded myself.

On the Jazzmaster, I wired one lead of the tone cap to the middle -- output -- lug of the volume pot and the other lead to the (looking down at the underside of the pickguard assembly (of a lefty guitar)) right-most lug of the tone pot.

The center lug of the tone pot has a bus wire soldered to it, that goes to ground.

The left lug of the tone pot is unused.

I've done continuity tests on the entire circuit and it all beeps at the desired places. The bridge is grounded, the trem is grounded, if I touch my test leads to any metallic part of the guitar (excepting the neck plate and the frets), I get a continuity beep.

???  :icon_scratch:  :help:

 

[TroubledTreble]

What kind of cap is that? Is it polarized? If it is you may try flipping it. dunno..

 

[reluctant-builder]

It's a NOS Russian Paper-in-Oil cap. I don't believe it's polarized.

I guess I'll just have to take it into my guitar tech.

Thanks.

 

[Jumble Jumble]

Surely a polarised cap is a no-no in a guitar?

 

[reluctant-builder]

How would I know, by the way, whether it is polarized? Would I be able to test that with my multimeter?

Still, I'm using those caps in other guitars, without issue ... so I'm highly dubious that's the problem.

One thing I do notice, though, is that if I touch the leads of the capacitor that's part of this suspect circuit, it buzzes at me ... at once point the amp even warbled, quite loudly; a sharp swell.

 

[TroubledTreble]

Polarized caps are for DC circuits. There should be markings on it to show it's polarized if it is.

I am suspect of some caps. There are some people out there who put generic caps into packaging that makes them look like other caps. They do this quite a bit to make caps look like PIO caps. So I hope you didn't get one of these.

 

[reluctant-builder]

So I hope you didn't get one of these.

Me too. :icon_biggrin: Damned snake-oil salesmen.