Faulty cap on bass? Or..?

slash-ed · Post by **slash-ed** » Mon Apr 16, 2007 10:24 am

I can't believe I've only just realised this... but this made itself quite apparent when I tried recording with my bass today.

When you're not touching the strings or bridge or whatever, there is that hum from bad shielding/ground/whatever, that usually goes away when you start playing. However I've noticed that it sort of takes a few seconds of muting the strings for it to fade away, and it sorta keeps coming and going as you play.

Am I right thinking this is something to do with the capacitor on the tone control? It fades significantly when turn the tone way down, it turns into quite a fully fledged buzz when it's on full.

Or is it just bad grounding in general and I should just rewire the thing?

foal30 · Post by **foal30** » Mon Apr 16, 2007 2:11 pm

is your bass two pick up and passive Ed?

foal30 · Post by **foal30** » Mon Apr 16, 2007 2:18 pm

heh I see the topic down now.
problem is I can only see one Pup and the description you use is Jazz?

I think your tone guess is the one... when you have a two pickup Bass passive, if the volumes are at different levels you get 60cycyle hum, it gets worse the higher the tone is up.

It's actually part of the charm, but i think you have cap/grounding issue because as soon as you put your fingers on the string it should kill the hum.

I also stand to be corrected on all of this too, so hold the phone good man.

slash-ed · Post by **slash-ed** » Mon Apr 16, 2007 2:43 pm

Ahh, the auction photo is wrong, it should be the one I posted further along that thread. Here's another link to it:

It may perhaps also be to do with the fact that only the neck pickup is currently working? I only realised later on that the bridge pickup was not working (hey, I dunno squat about bass

)...

Those J-Bass pickups are basically single coils, right? So I guess the hum is expected, but it's rather louder than I'd thought it would be using just a straight up clean tone, but then again I have no prior experiences with basses.

Rog · Post by **Rog** » Mon Apr 16, 2007 4:35 pm

Bassically

most bass players with passive basses leave the tone control on full anyway.

If only one pup is working, it is possible that you have an open circuit on t'other. If that be the case, of course it'll hum.

In NZ we don't get 60 cycle hum!

foal30 · Post by **foal30** » Mon Apr 16, 2007 5:23 pm

240 Hum?
is it 4x worse?
you know what I mean.

never have your tone on, thats my motto.

slash-ed · Post by **slash-ed** » Mon Apr 16, 2007 5:26 pm

Ah. Currently rewiring, hopefully it will work.

It's a wonder it was working at all, none of the pots were properly grounded.

Underneath the pickups, and at the bottom of the control route, there are these brass looking plates that were grounded - is this commin?

slash-ed · Post by **slash-ed** » Mon Apr 16, 2007 6:15 pm

No luck - it is still doing the exact same thing, and the bridge pickup is still dead.

B45-12 · Post by **B45-12** » Tue Apr 17, 2007 12:03 pm

Try resoldering/swapping over pup wired to vol control (just the middle ones - the braided outer ones can be left where they are) and see if the same pup is still dead. If not the fault is elsewhere. If it is then put a multimeter (Dick Smith have them for $20 or you could probably nick/borrow one from the University's electical lab) on ohms reading scale (select 20k's or higher) across the leads from the suspect pup if it shows 20k or higher the pu's open circuit; if under 20k (usually about 7-10k) it's OK.

B45-12 · Post by **B45-12** » Tue Apr 17, 2007 12:10 pm

foal30 wrote:240 Hum?
is it 4x worse?
you know what I mean.

never have your tone on, thats my motto.

No - it's 50 cycle hum in NZ since that's the mains frequency here - in the US it's typically 115volts at 60 cycles - typical yanks you get a higher pitch of noise/mains hum on your amp there

Tone 'on' actually only removes the highs/trebly componenet of the pup - won't do nothing to the mains hum (or should not!!). Basically it shorts out the higher frequencies by a variable resistor and capacitor in series across the pup leads - the cap lets through the high frequencies (but not the low) and the resistor lets more or less of them through to earth so they don't reach your amp.

slash-ed · Post by **slash-ed** » Tue Apr 17, 2007 2:48 pm

B45-12 wrote:Try resoldering/swapping over pup wired to vol control (just the middle ones - the braided outer ones can be left where they are) and see if the same pup is still dead. If not the fault is elsewhere. If it is then put a multimeter (Dick Smith have them for $20 or you could probably nick/borrow one from the University's electical lab) on ohms reading scale (select 20k's or higher) across the leads from the suspect pup if it shows 20k or higher the pu's open circuit; if under 20k (usually about 7-10k) it's OK.

Ahh, you were exactly right... The 2nd volume pot is dead, I think.

On the other hand, the bridge pickup seems massively softer when going than the neck one does. Should I swap them round when I rewire it?

foal30 · Post by **foal30** » Tue Apr 17, 2007 2:52 pm

ace legend post Man.
Don't actually understand too much of it, but I feel more knowledgeable.
this is important.

Almost as important as Trade Unions in fact.

slash-ed · Post by **slash-ed** » Tue Apr 17, 2007 3:17 pm

Is it okay to use 500k pots on it? It comes with 250k pots all round is why I'm asking...

slash-ed · Post by **slash-ed** » Tue Apr 17, 2007 11:38 pm

Ok I tried switching the pickups round cos the bridge one sounded soft... but lo and behold - they don't fit!!! Are J-bass pickups generally like that, or is it just bad QC on 1976 Hoshino's part?

Rog · Post by **Rog** » Wed Apr 18, 2007 8:09 am

A well designed bass will have both pups different sizes, to accomodate the wider string spacings nearer the bridge.