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I am struggling with hum on my archtop that has a Kent Armstrong HJGS-1 floating pickup. If we touch the outside plastic covering of the pickup or to the ground lug on the pickup, the hum reduces dramatically so it seems like a grounding issue.

What I've tried:

  • I replaced all of the wires in the guitar but no change.
  • I pulled the pickup off the guitar and soldiered new 4" wires directly to a jack, the hum is still evident.
  • We've tried multiple amps. We've moved the guitar around the house. We've compared the hum with another guitar on the same amp with the same 1/4" cable. No hum.

I've done a ton of reading on the subject but I'm stumped.

Questions:

  1. Is it possible that the pickup is indeed generating the hum? Maybe there is some grounding issue internal to the pickup?

  2. Any addition ways we can test the pickup to make it is the problem? It shows something like 7.9k ohms and I've figured out the polarity using the metal whack test but otherwise i'm not sure what to try.

Thanks for any help.

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  • My guitar is able to be kinda radio, catching waves.😉 Some guys suggested me to isolate "hardware stuff" in body with a foil.
    – max.kuzmentsov
    Commented May 19, 2016 at 6:27
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    1) Typically hum is due to faulty grounding, but this could possibly be because of a faulty pickup. 2) What happens when you touch the strings, or when you switch the pickup in and out? 3) this is really the important question here - I'd suggest asking it separately. Grounding is essential - doing it wrong will give hum.
    – Doktor Mayhem ♦
    Commented May 19, 2016 at 8:40
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    Thanks for the feedback @DrMayhem. I've moved my #3 question to it's own: music.stackexchange.com/questions/44613/…
    – Gray
    Commented May 19, 2016 at 20:01

1 Answer 1

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I'm certainly not an authority but I can at least detail what I've learned so far.

  1. Although I bet it is possible for the pickup to be at fault, in my case I'm pretty sure by now that this was a wiring/grounding problem. Replacing the wire with the 18 gauge shielded wire made a big different right off the bat. Before I was using a single-core 22 gauge cat5 style wire which made the hum worse. It also seems like joining the negative and ground wire makes a big difference as well although I'm still learning about this.

  2. In terms of grounding, I'm not sure how to test the pickup. After doing some more searching I found this great guitar pickup polarity test page which showed how to test the polarity of the pickup by watching the DC voltage on the pickup when it is struck (nicely) with a metal screw-driver. You should get a positive DC voltage when the metal goes into the pickup and a negative deflection when it is removed.

I also started another question about the proper way to use a shield and ground-wire when rewiring a guitar.

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