P bass connoisseurs - ground/shielding issues?

[fingerz]

Can anyone help with what is no doubt a very simple problem on a very simple instrument.

A JV Squire P Bass 1982 I've just picked up is quite noisey and will pick up interference from my laptop screen etc and is very sensitive to environmental noise/magnetic interference. Some pointers to help isolate this:

- Tone control effects level of noise (of course!)
- Very loud when I take my hands off the bass, but a similar noise when I'm grounding it just less of it, suspect I need to improve ground?
- Tone pot is a little funny, i.e. opens up towards the 'closed' end of the control. - maybe the track is loosing contact and effecting ground here?
- Seems less when volume is full up
- no copper shielding inside cavity
- not microphonic

Knowing the P bass configuration, I am sure I can get this to be very quiet, just as all P's are. It's all standard/original apart from the Jack socket.

Would love to get this sorted before I gig it just incase I get caught out. Never take a problem out on a gig - that's my motto!


Thanks very very much in advance,


Fingerz

[KingBollock]

If it was me I'd shield the cavity first, though I suspect it'll take more than that from the way you describe it. Then I'd replace all the pots and wiring. If this sorts it out but you want it as original as it can be, you could use the new parts to eliminate the faulty part and then only replace that.
Even good pots don't cost much so buying all new parts won't be expensive. In the end, if you only end up replacing one pot, you'll then have spares.

[Lozz196]

I had a bit of a buzzing issue on my 78 Precision and did exactly as above, plus put shielding tape all over the underside of the scratchplate. Sorted, no problems now.

It`s actually good advice as well to change pots/capacitor/jack as get the wear on the new ones installed, so keeping the original stock items for if/when you decide to move it on.

[fingerz]

Thanks guys, really helpful.

Where do you get your pots from? And I assume the rating will be on the pot if I take it off.

Shielding wise, copper is best, again where do you get it from? Also, if I put it underneath the scratch plate, does is have to connect to any conductive part within the cavity? Or is is literally simply acting as a defence just being there?

[HowieBass]

If you're going to shield the bass and replace the pots then you may as well just check the bridge ground wire is in good contact as well.

EDIT: Though I've never had to shield any of my own basses with foil under the scratchplate I think if you bring some foil up from a cavity to just lie next to/over one of the scratchplate mounting screw holes then when you screw down the plate you'll get contact in that area.

Edited December 15, 2014 by HowieBass

[fingerz]

if I touch any conductive part of the bass in isolation then it grounds it, I'm assuming (hoping) that means they are all in good contact. I think I might try that pesky tone pot as a first point. If I can get one locally then I could get on with it tomorrow.

[HowieBass]

I'd suggest you check the soldering on the ground wires, particularly the jack socket before you replace the tone pot.

[fingerz]

[quote name='HowieBass' timestamp='1418675096' post='2632273']
I'd suggest you check the soldering on the ground wires, particularly the jack socket before you replace the tone pot.
[/quote]

Thanks dude

[fingerz]

[quote name='KingBollock' timestamp='1418669772' post='2632193']
If it was me I'd shield the cavity first, though I suspect it'll take more than that from the way you describe it. Then I'd replace all the pots and wiring. If this sorts it out but you want it as original as it can be, you could use the new parts to eliminate the faulty part and then only replace that.
Even good pots don't cost much so buying all new parts won't be expensive. In the end, if you only end up replacing one pot, you'll then have spares.
[/quote]


Very important to say what I've learnt/done:

The CTS pots are serviceable, or rather, come apart so you can clean them. Especially with an older instrument, it's better to keep things stock. Took the one pot out, cleaned it all up, insulated the underside of the pick guard which makes contact with the pot fastening nuts. Soldered it back together and it's dead quiet and tone pot working perfectly.

I might do a step by step topic on this as I found limited info especially regarding pots/cleaning.

Thanks for all the help guys.

[HowieBass]

Great news! Now make some noise

[Telebass]

It's also important to remember that a Precision has a humbucking pickup. I've found that quite often, either the pickup output wiring is wrong, on one pickup segment is back to front. Correcting that alone can sonetimes eliminate all noise, even with no cavity shielding.

[fingerz]

Thanks Telebass.

Exactly, that humbucker is a sound bet for noise rejection - funny that you've had ones wired incorrectly, how weird? Did they sound different when re-wired?

For me, the pup was wired correctly, I think the pot would loose ground when the wiper was out of contact with the track (Possibly BS but in my mind that could be possible..!!), but I added some copper tape to the back of the guard which I brought round and up to the jack socket at the same time as pot strip and clean. Just around the pup area and over the pots (this connection to ground here is very necessary)..Therefore I can't tell what resolved the noise, but it's very very good now. No shielding needed in the cavity. Thanks though, that's handy to watch out for.

[Billy Apple]

I've got a JV that I got a pro to replace the harness, pup and shield everything. It's all been done so all can be returned to stock if need be. Mind you, it sounds monumental and can't think I'd ever want to put it back.

[Marc S]

[quote name='KingBollock' timestamp='1418669772' post='2632193']
If it was me I'd shield the cavity first.....
[/quote]

My first thoughts too...
Definitely a good starting point
I believe the later Japan-built "non-export" models were very well shielded in that respect...

As others have said, check the rest of your wiring / connections too
It is possible that you have a slight dry joint somewhere
I always solder using flux these days

I'm no particular expert at soldering or electronics, but I have done a fair bit in recent years
Most solders contain flux, but applying liquid flux to a joint, just before soldering, improves matters
and speeds up the action of the solder

Check that bridge earth wire too
I recently bought a Fender pot, from a local shop
and it wasn't too expensive...

Good luck anyhow

[fingerz]

Cheers guys. All great info.

As stated above in previous posts, I've done all the work myself, and it's all sorted. No need to replace cts pots, they are serviceable, so if your tech won't do it, you certainly should! A pots a pot, as long as it's working and free from crap it's not going to sound any better/worse than the next one - really important to have original parts IMO.

Edited December 19, 2014 by fingerz

[Ghost_Bass]

I would start by unplugging the laptop from the mains first. Don't know how it works in UK but over here the laptops PSU's introduce a lot of interference in audio gear (most noticeable on bass cab tweeters).

Edited December 19, 2014 by Ghost_Bass

[fingerz]

[quote name='Ghost_Bass' timestamp='1419005494' post='2635668']
I would start by unplugging the laptop from the mains first. Don't know how it works in UK but over here the laptops PSU's introduce a lot of interference in audio gear (most noticeable on bass cab tweeters).
[/quote]

For me, any interference I can get in the environment I am testing the bass, is a good thing. I want noise rejection to be great on my basses as they get used in lots of high intensity environments. So the laptop was a good test against other basses I know work well. I think we are missing the point here! A desk lamp where I was soldering the bass was a good one to aggravate it. Smartphones and Laptop screens do drive basses crazy too. Thanks for the input mate.