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Vintage modified Jazz bass wiring problem

E

eire87

Jul 18, 2011
23
0
#1
Hi all,

I bought a second hand VM jazz bass yesterday and took it jamming last night. I found that when the lead went a certain way there was that 'crackling' horrible noise and a loud humming. The kind of thing that happens when you have a dodgy lead. I switched leads to one I know works and still the same problem.

Then...

While we were playing a little later I started to hear a radio station coming through the amp (I thought I was losing my mind big time before I eventually told every body to shhhhh and they could hear it too!)

Iv removed the control plate to see if there were any broken connections but I cant see any.

I searched the forum and came across a .pdf showing how a VMJ should be wired and mine seems to be a little different.

I was hoping to tap into the TB brain trust and see if anybody could shed a little light on what might be the cause.

Iv taken pictures so hopefully they help diagnose the problem!

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Any help would be most appreciated!
 
#3
What you are probably seeing as "a little different" is all of the ground wires soldered to one pot. This is done on all of the VM jazzes I have and is not a problem. It's tough to tell where the other lead of the tone control capacitor is wired because of the picture quality. Does the tone control work properly? Make sure that is soldered to the correct lead on that pot.
Other than that, I would plug the bass in to an amp and touch the wiring on the pots to see if there is a loose one. The one solder joint on the tone capacitor looks a little sketchy.
 
#4
The tone pot works fine, I tried plugging the bass into an amp while leaving the control plate unscrewed, when it starts humming and crackling if i touch the pots with my fingers sometimes it stops but this result is not consistent.

If I wiggle the lead when it's plugged into the bass it can make the electrics start acting up (making the noises). Iv checked and there is really good contact with the input jack and the lead.

I'm totally stumped :-(

I will take better quality picks tomorrow to give a better view.

I wanted to gig this bass this weekend to test it out but it's too unpredictable.... Damn it :-(
 
#5
One suspect for the humming may be the ground lead under the bridge. Loosen the strings up and remove the bridge to see if the ground wire underneath is making a good connection to the bridge. Just an FYI...what you're calling the "input" jack is the "output" jack...and since we're on that subject, that may need to be replaced. As far as the crackling goes, you may need to clean the pots. Sometimes just working the pots(rotating them back and forth multiple times) will clean them. Hope this helps.
 
#6
Hi audioglen, thanks for all your help and suggestions, I replaced the output jack (thanks for the FYI ;-)) and checked the ground under the bridge. The ground under the bridge was just a wire and I can't see how it's not in full contact with the bridge when the bridge is on place.

The problem is still there though :-( there is no noise extra noise when I turn the volume and tone pots only when I move the cable in the output jack.

It's so weird...

Any other suggestions or should I bite the bullet and get new electronics?
 
#7
Yup...this is a tough one! Well, if I were you, I would get new pots and capacitor and rewire it. It's an easy thing to do. That one solder point on the capacitor to the back of the the tone pot really looks bad. Do you have a tech who can take a look at it for you? You may want to do that before you buy any parts. Let me know what happens.
 
#8
There arent many techs near me and any that are wont be able to sort me out for a few weeks.
I think I will just buy a new wiring kit and rewire the bass. Do you think it could be anything to do with the pickups themselves because if they could be the problem I would probably buy new pickups that come with new electrics aswell?

Would any standard Jazz wiring kit do the trick or is there certain kits that I should steer clear from?

Thanks again for your help audioglenn its much appreciated!:)
 
#9
is it just me, or does it look like the other 2 pots need to be grounded?
also, the tone cap looks to be connected to the ground lead of the output jack? (my experience tells me that it should have one lead to ground and the other wired to the "full on" lead of the pot.) Also the solder join on the tone pot looks like a "cold solder joint", when soldering is done properly it should be shiny, similar to the other solder blobs. Not a dull grey like it appears in the picture.
 
#10
As audioglenn said that is how any VMJ bass he has had has been wired and he hasnt had a problem but then again ill try anything!

Could you maybe tell me what I would wire to where? I am comfortable soldering and love a project ;-)
 
#12
Does the problem go away when you kill either of the pickups? It seems to be wired correctly. The solder joint that takes the cap to ground looks terrible, but that wouldn't be in the circuit with the tone knob at 10.

It almost sounds like you have a pickup that has gone microphonic on you.
 
#13
Thanks for your suggestions braud357, tomorrow I am going to resolder all the joints and replace any wires that I can. Hopefully that does the trick!

Hopkins, no the problem stays no matter what orientation/ combination I have any of the knobs. It only happens when I touch/ move the cable in the output jack. I thought replacing the output jack would solve the problem but it didnt make the slight bit of difference.

Iv never heard of a pickup becoming microphonic, is this a common isuue. From the looks of the bass it looks like it hasnt been kept in ideal conditions. all the screws holding the pickguard and control plate has discoloration/rust on them and the pole pieces on the pups also have the same.

I may have been a bit too eager when buying... lesson learned!
 
#14
eire87 said:
Thanks for your suggestions braud357, tomorrow I am going to resolder all the joints and replace any wires that I can. Hopefully that does the trick!

Hopkins, no the problem stays no matter what orientation/ combination I have any of the knobs. It only happens when I touch/ move the cable in the output jack. I thought replacing the output jack would solve the problem but it didnt make the slight bit of difference.

Iv never heard of a pickup becoming microphonic, is this a common isuue. From the looks of the bass it looks like it hasnt been kept in ideal conditions. all the screws holding the pickguard and control plate has discoloration/rust on them and the pole pieces on the pups also have the same.

I may have been a bit too eager when buying... lesson learned!
Click to expand...

Since it happens with both pickups on, I doubt the pickups are the problem. I am assuming you have tried different cables and had the same issue.

Try, to bend the connection that makes contact with the tip of the cable downward, so it makes a tighter connection with your cable. Also what might help is to take the pots and jack off of the control plate and make sure there is no corrosion where they connect to the plate.

Picking up radio noises is what made me think you might have a microphonic pickup, which can be caused by them not being potted. Whatever your problem is, its not going to be that big of a deal. You could swap out all the parts in that bass for less than $100. As long as it plays well, you are good.
 
#15
… or you could go shopping and do some serious tonal upgrades as well as modifications on that bass. And although I think the original pickups on them are really good (I own one), I do plan on some electronics upgrades in the near future, specifically the tone circuit and swapping out the Duncan Designed pickups for Quarter Pounders.
 
#16
Not a bad idea and I'm keeping my eye open on the classifieds for something nice but I'm kinda stubborn and its getting to be one of those things where I really want to get to the bottom of.

As well as the electronics acting the goat I can't seem to get the action to where I'd like it to be. I know it's not a top end bass but Iv heard nothing but great things about them and that's why I bought it.

Iv set up all of my other basses great but this one seems to be giving me trouble on all fronts.

I do love the look of it though so I'm not giving up :-)
 
#18
What I'd be tempted to try is using alligator jumper wires to hook in to the amp at electrical points closer to the pickups until the issue goes away... Then look immediately downstream for the issue.

If you can figure out the rewire and replace jacks you should be able to figure the procedure I've described above out...
 
#19
A friend of mine had similar problem. I traced it back to the pickups. The copper wraps ( the winding) was loose still touching but shorting out. Use a magnifying glass. Good luck. I ended up buying new pickups.
 

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