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Diagnosing problem with a Bass Guitar
Old 8th September 2012
  #1
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aj633's Avatar
 
🎧 10 years
Diagnosing problem with a Bass Guitar

I have a '70s P Bass that's having issues. I've been putting off looking at it, but it's time. I think the problem has to do with the input jack/wiring. The bass will play for a couple minutes and then make a screaming loud noise like a guitar feeding back, but lower frequencies. Touching the 1/4" cable then makes loud clicking noises. What should I be looking for? Should I just re-solder the input jack? Is this a common problem?
Old 8th September 2012
  #2
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1 Review written
🎧 10 years
If it's a passive P bass, it's probably not the bass. If it's active, the battery might be flat or the preamp faulty. But really, I would look at the amp or signal chain you are connecting it to. For it to play ok for a couple of minutes makes me suspect a battery problem. Or possibly a heating up problem, like a capacitor or tube or some other AC power component failing as it warms up.

Isolate each component until you remove the problem.
Old 8th September 2012
  #3
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🎧 10 years
It happens with different amps and cables. It is passive.
Old 8th September 2012
  #4
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🎧 10 years
If it were a short in the input jack, it would sound like if you touched the end of a 1/4" jack while it was plugged in to an amp - or it would make no sound at all. That has been my experience. Could it be that the pickups have gone microphonic? although that would not take a few minutes to act up. a cold solder joint on any of the grounds inside connecting the pots and bridge?


It doesn't take much to open a P'bass up and just have a look. Take off all the screws for the pick guard and try slipping it aside to see if there is anything obvious.
Old 8th September 2012
  #5
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🎧 10 years
That's the sound. Just louder.
Old 9th September 2012
  #6
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🎧 10 years
If it's a classic P bass pickup, it's a single coil. These are extremely prone to picking up external EMI. Your statement that it will "play for a couple of minutes" is a bit weird, because passive pickups don't really warm up and change much like an active circuit can.

I would experiment to see if the behaviour changes if you buffer it with a pedal or something. And whether the sound changes with direction, if it is external EMI it might. Then again - it might be ground noise which won't change with direction.

Capacitors/condensors are the most likely things to fail and short out - I would replace that first if I really thought the guitar itself was faulty. With most of my Fender basses i've replaced the single coil pups with Duncan stacked pups - wired direct to the jack, because I see no need for volume or tone controls to suck tone and level. I prefer to control levels and tone externally.
Old 9th September 2012
  #7
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ForgottenG's Avatar
 
🎧 10 years
Sounds like a wiring issue. Take it to a tech and have him check the wiring. Usually this is a grounding issue. Make sure your input jack is tightened down and not moving.
Old 9th September 2012
  #8
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🎧 10 years
Output jack
Old 9th September 2012
  #9
Here for the gear
 
🎧 5 years
Quote:
Originally Posted by Hyder boy ➑️
Output jack
This. The pbass has about 6 solder joints, and the output jack is the culprit about 95% of the time. Take off the strings, remove the oil guard, and re solder the out put jack. Should take less tha half an hour. Then it'll be good for another thirty years
Old 9th September 2012
  #10
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cavemusic's Avatar
 
🎧 10 years
As posted above, the first thing to check is the wiring, since that is most likely. Another possibility is pickup failure. I also have a 70s P bass, and the pickup (one half of the split pickup) did in fact fail after about 25 years so I had to replace it. I've heard that the quality control on Fender pickups was kind of poor for part of the seventies.
Old 9th September 2012 | Show parent
  #11
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ForgottenG's Avatar
 
🎧 10 years
Quote:
Originally Posted by ForgottenG ➑️
Sounds like a wiring issue. Take it to a tech and have him check the wiring. Usually this is a grounding issue. Make sure your input jack is tightened down and not moving.
oops. Thank you all. The output jack is what I was saying. Do as I think, not as I say.
Old 12th September 2012
  #12
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aj633's Avatar
 
🎧 10 years
Tried resoldering the jack. May not have done the best job. Still a problem. See video:

http://www.youtube.com/watch?v=jekV-...e_gdata_player
Old 12th September 2012
  #13
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🎧 10 years
I guess you'd want to check all of the wiring right from the pickups to the jack including the potentiometers. Try wiggling the knobs to see if that causes something. Try tapping the pickups. Sounds like something shorting out intermittently. It could even be shorting out inside the pickups themselves.
Old 13th September 2012 | Show parent
  #14
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Jeff Scott's Avatar
 
🎧 10 years
Quote:
Originally Posted by Kiwi ➑️
If it's a classic P bass pickup, it's a single coil.
The OP says it is a '70s P Bass, so the pickup is a split humbucking pickup.

Sounds like a ground problem, to me. As mentioned above, check all the solder connections for a bad connection, first, then suspect the pickup going bad, possibly. And, check the tension on the output jack's tangs, to ensure a tight fit with your cable's plug.
Old 21st September 2012 | Show parent
  #15
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Hot Vibrato's Avatar
 
🎧 5 years
Quote:
Originally Posted by cavemusic ➑️
Another possibility is pickup failure....
Pickup failure is relatively rare on old fenders, but it DOES happen sometimes. If this is the case - two words: Lindy Fralin

Lindy has probably rewound more vintage vintage pickups than anybody out there.

Usually when a pickup fails, the result is very weak, or no output. I've never heard a bad pickup sound like THAT. It's probably something that an experienced tech can fix in half an hour.

My guess is (also) the output jack. It's a $3.00 part. Replace it.
Old 23rd September 2012
  #16
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aj633's Avatar
 
🎧 10 years
I finally replaced the jack today and touched up a couple of the solder connections. Seems to have done the trick. We'll see...
Old 10th November 2012
  #17
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🎧 10 years
So in case anyone looks back at this, the jack was only part of the problem. As it turns out, there was no ground on the jack. Not sure how or when that happened...
Old 11th November 2012
  #18
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John Eppstein's Avatar
 
58 Reviews written
🎧 10 years
Make sure there's a ground wire running to the hardware. There should be a single wire, probably bare, that runs between either ground on the jack or the grounded case of one of the pots through a little bitty hole that comes up under the bridge for the ground. If this is disconnected noise problems can ensue.

The wire is not actually soldered to the bridge, just pressed between the metal plate and the body.
Old 11th November 2012
  #19
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aj633's Avatar
 
🎧 10 years
Yeah, it's fixed. I'm not sure what happened to the wire. Maybe it disintegrated or was never there...
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