Electrical Gremlin

[Mulldoe]

Hi everyone, any electrical geniuses out there? I have a hum in my LP that I can't work out, thought I might of cooked a pot while I was soldering at first so I ended up ordering an epiphone harness for it. I chucked that in and the hum reduced a bit but was still there, I noticed it stops completely when I touch the housing at the end of the cable but touching anywhere else has no effect on it. I know it isn't the cables themselves because my other guitar doesn't hum at all. Any thoughts or suggestions would be greatly appreciated.

Cheers, Mulldoe.


Okay so the issue was that the strings weren't grounding, the problem was the paint on the black tune o matic hardware was breaking the continuity. The solution was pretty simple in the end, I just had to scrape some paint off of the saddle post and inside the saddle "hooks". Such a simple fix for what took me forever to figure out, cheers for the advice dingo and fender.

[dingobass]

Sounds like an earthing issue..
Have you shielded all cavities?

[Mulldoe]

Hi db, nah I haven't shielded the cavity or anything, I did try manually grounding the switch etc with another wire and that didn't reduce the hum.

[dingobass]

OK, try shielding the cavity and see how that goes.
With all those wires running around in the LP's you are bound to get some hums and buzzez if it isnt shielded.

[Mulldoe]

Cool, cheers mate I will give that a go.

[fender3x]

I agree with DB. It's most likely a ground issue or RF interference. Either way the shielding will help.

You could also test to see if everything is grounded with a multimeter. Turn the meter to one of the high ohm settings, like 2000K or 200K.

A digital meter will register 1 with the test leads apart. It will read close to 0 with them touching.

Clip one test lead to the ring on your jack. With the other lead touch everything that should be gounded. Anything properly grounded will register near 0 when you touch it.

Things to touch include:

The ground wires from both pups.

The metal housings of all pots.

The strings.

The chrome housings on your pups (if you have them).

The switch if it has a metal housing.

Any shielding (e.g. pup baseplates, wire braid covering wires, cavity shielding if you've added it.)

If it still hums after you have fixed all that you could try potting the pups or...

You could plug a different guitar into your amp. If it still hums it's not the guitar, it's the amp. If it's the amp, slap your palm on your forehead and shout "Why didn't I check that first!" ;-)

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[Mulldoe]

I agree with DB. It's most likely a ground issue or RF interference. Either way the shielding will help.

You could also test to see if everything is grounded with a multimeter. Turn the meter to one of the high ohm settings, like 2000K or 200K.

A digital meter will register 1 with the test leads apart. It will read close to 0 with them touching.

Clip one test lead to the ring on your jack. With the other lead touch everything that should be gounded. Anything properly grounded will register near 0 when you touch it.

Things to touch include:

The ground wires from both pups.

The metal housings of all pots.

The strings.

The chrome housings on your pups (if you have them).

The switch if it has a metal housing.

Any shielding (e.g. pup baseplates, wire braid covering wires, cavity shielding if you've added it.)

If it still hums after you have fixed all that you could try potting the pups or...

You could plug a different guitar into your amp. If it still hums it's not the guitar, it's the amp. If it's the amp, slap your palm on your forehead and shout "Why didn't I check that first!" ;-)

Sent from my SAMSUNG-SM-N900A using Tapatalk

Cheers fender3x, it's definitely not the amp I have tested on 2 amps and with 2 different guitars and this is the only one that hums, the other is dead quiet. Just finished shielding the cavity and still have the hum, it does stop when I touch the metal around the end of the lead or the spindle on the tone pots. I guess I will go and test all those metal components you mentioned and go from there. Thanks for the input mate.

[fender3x]

Looking like a ground problem alright. When you touch, you become the ground and the hum stops.

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[Mulldoe]

Looking like a ground problem alright. When you touch, you become the ground and the hum stops.

Sent from my SAMSUNG-SM-N900A using Tapatalk

Yeah cheers mate, borrowed a multimeter and found out the strings weren't grounding. This guitar has black tune o matic bridge and the paint was breaking continuity. Scraped some paint off the saddle and saddle post where it can't be seen and the problem was solved. Thanks again mate.

[fender3x]

Great that you found it! It occurs to me that you might want to check each string individually to make sure they are all grounded. I had forgotten how tricky those black bridges can be.

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