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I've started playing bass using an old one my father owned. It has not been serviced for ages as far as I know. I've plugged it in to a new Vox Pathfinder practice amp with a new cable.

I notice that as well as some crackles from the knobs (expected) I can get a pretty loud hum when I hold it with all strings open. If I mute them all, it stops. If I remove my hand, it builds up over a few seconds.

Is this feedback resonance or mains-hum or something else that needs fixing on the guitar? I am not playing with a particularly loud amp and am probably about 6 feet (2m) away.

Update: I was interested to see what makes the hum start and stop. I discovered that touching any individual string does not make much difference. However touching the bridge does. Someone mentioned grounding Vs resonance, I'm not sure what this tells you because equally, touching the bridge might be enough to damp the resonance?

  • The "building up" part certainly sounds like feedback. Does it KEEP building up? – Laurence Payne Jun 19 '16 at 18:20
  • It could be a combination of mains hum and acoustic feedback. When you take your hand off the strings, does the hum start immediately? What about if you keep your hand on another part of the instrument that should be grounded, like the bridge? – topo Reinstate Monica Jun 19 '16 at 19:26
  • If it's feedback, it'll most likely be only one string vibrating. Which one - or is it all? – Tim Jun 20 '16 at 6:46
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    You could put a tuner in front of the amp. 60Hz mains hum is slightly sharp of A#, 50Hz is sharp of G#. Neither note would be a good one to really induce sympathetic resonance in a bass tuned correctly. If the amp you mentioned wasn't such a simple design, I'd be more inclined to suspect a compressor was creating the rise in hum volume over time. – Tetsujin Jun 20 '16 at 7:00
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    It does sound like compression, but also, many pickups act as "ambient antennas". If you stand up with the bass and rotate 90 or 180 degrees, can you affect the sound? – Yorik Jun 21 '16 at 14:24
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In an old instrument, solder connections can get knocked around and become brittle if not done well. Bad shielding and bad grounding is a common issue with instruments and their lead cables.

Check your solder connections inside the control cavity of your bass. Look specifically for the wire that leads from the top of a potentiometer to the bridge. That is your ground and should be super secure and well soldered. Then look for a good connection on your instrument cable jack. Good solder joints will be shiny and smooth.

If any of these connections, and anything in between, are not solid connections, your bass has a bad ground and is using your body as its new ground when you touch its electrical components. If these connections are all fine, check your instrument cable ends for good connections too.

Good luck! For what it's worth, soldering is a great skill to learn for guitar issues.

  • Thanks. I'm probably gonna take it to my local luthier because the potentiometers likely need replacing unless a bit of WD40 stops the crackles. But I agree ideally I'd do this myself if I had the time, the electronics are quite rudimentary? – Mr. Boy Jun 21 '16 at 10:30
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    What you need for "dirty pots" as it is often called, is just a can of DeoxIt. It's all over Amazon and is highly useful on all electronics (ie cellphone ports). All you have to do is spray in a crevasse in the back of the pot and it will de-oxidize and clean the moving connection inside. You're lucky to have a local luthier, that is non-existent in my area. Not everyone knows the electronics. I know many musicians who don't care to and would shell out money for professionals to do an easy job. It takes research and curiosity, but well worth the knowledge. Google is your best friend – ImmutableDusk Jun 22 '16 at 18:52
  • +1 This does sound very much like bad ground in the guitar itself. Redoing the connections should fix the problem. – user321 Sep 19 '16 at 17:40
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You might also want to shield your electronics from RF, if it turns out to be more than just a grounding issue. NoTreble has a handy guide here: http://www.notreble.com/buzz/2011/09/20/the-buzz-killer-how-to-shield-your-bass/ and copper tape is fairly cheap from Stewart McDonald.

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