#1
Hi everyone.

I recently built my own guitar from spare/secondhand parts. (It has 2 humbuckers, a tele control plate, a trapeze tail, and a metal jack plate. A ground wire runs to the bridge.) I did the electrics myself, and was originally testing it out on a small 2-watt, battery powered Danelectro mini-amp. Everything sounded fine -- no ground hum to be found, even with volume cranked or in overdrive.

This weekend, i went to a pawnshop and found a Washburn Bad Dog 25 watt practice amp. I got it home and plugged in my guitar. On clean settings, everything sounded fine. But when I cranked the volume real high, or applied Overdrive, I got the typical ground hum. The hum disappeared when I touched either the jack plate or the adjustable screws in the pickups; touching the bridge, control plate, or pickup poles made no change.

I'm concerned that I didn't solder things properly, but I'm also wondering if I bought an amp that has a grounding issue. I've been on other forums, and the advice I heard goes between those two, so I thought I might open it up here. Thoughts?
#2
It is pretty normal for a guitar to produce hum when you don't touch it. But it is also normal that this hum greatly is reduced when you touch any of metal parts on the guitar.
I'd check the grounding of every part in your guitar. Also it can use screening. I suggest good ol' copper foil of about 0.1mm thick.
#3
Well, that's all good info to know.

By screening, do you mean shielding tape or screened wire? I would like to be able to shield-tape the instrument, but... Well, it's kind of a non-traditional instrument. It's a sketch box/paintbox that I've turned into a semi-hollow guitar. I'm not sure how easy this would be to apply a good amount of shield tape...

#5
In your case I suppose there is some broken solder joint or wire since touching the bridge has no effect at all.

And by screening I meant putting all the cavities that contain any wires in an enclosed envelope of copper foil. In other words - you can glue copper foil onto walls and floors of the cavities and make sure they all have electric contact.
I usually do a sketch cutout in paper and try to fit it in. With small corrections I cut the same shapes out of the foil, glue it in and then solder in a few spots - just to make sure.
This gives some good results comparing to emilac and other similar ways to shield the electronics from interference since copper makes a good conductor.
Don't pick thick foil thouh - it can degrade guitar's sustain though a little.

Good luck.
#6
This might be an idiot's question but... Might that hum have anything to do the inch length of unsheathed ground wire from one of the pickups? The hum goes away when i touch the exposed part of the wire.
#7
anything you touch that is part of the ground will have the same effect. touching that portion of wire is the same as touching the bridge or strings. it all stops the hum.
you can check for metal parts that when you touch them they DONT stop the hum. then ground them. i can guarantee it will solve it, but it can only help it. stuff like the toggle switch housing.
#8
I can see straight away you have black hardware. I can't imagine the black paint on that being a good conductor for ground. Take an ohm meter and check continuity from the strings to the ground. It should be very close to 0, like 1.2 ohms or something. if it's just blank, then I bet you have a problem with your ground to the strings. Maybe run your ground to your tailpiece rather than your bridge, because I bet that chrome would be a way better conductor than the black hardware.
#9
Quote by LeviMan_2001
I can see straight away you have black hardware. I can't imagine the black paint on that being a good conductor for ground. Take an ohm meter and check continuity from the strings to the ground. It should be very close to 0, like 1.2 ohms or something. if it's just blank, then I bet you have a problem with your ground to the strings. Maybe run your ground to your tailpiece rather than your bridge, because I bet that chrome would be a way better conductor than the black hardware.


unless its cheap hardware, it actually conducts just fine - im not sure what its made of or how it was done, but my black hardware conducts great, ive tested it. if its simply painted, that would definitely be an issue. but they have magical black chrome or something
#11
Quote by scottythered
. But when I cranked the volume real high, or applied Overdrive, I got the typical ground hum. The hum disappeared when I touched either the jack plate or the adjustable screws in the pickups; touching the bridge, control plate, or pickup poles made no change.

Thoughts?


Pickup poles won't make a lot of difference unless youve gone out of your way to ground each pole.

However, your bridge clearly isn't grounded as you should have noticed a difference similar to touching the input jack plate. You WANT your strings and bridge to be well grounded because along with the reduced hum factor, it's also a safety issue.

Get hold of a multimeter and double check your bridge continuity all the way back to your input jack plate.

If you have to open the guitar again, just bite the bullet, do it properly and star ground all your conductive components back to a common point, like the input jack plate.
Last edited by Phoenix V at Oct 4, 2011,
#12
Quote by Phoenix V
However, your bridge clearly isn't grounded as you should have noticed a difference similar to touching the input jack plate. You WANT your strings and bridge to be well grounded because along with the reduced hum factor, it's also a safety issue.

If you have to open the guitar again, just bite the bullet, do it properly and star ground all your conductive components back to a common point, like the input jack plate.

Well, I opened it up and rewired things, redoing some of the grounding on the volume pot, but mainly moving the ground to the tailpiece. On clean settings, the guitar is fine. When I turn on the amp's overdrive, however, there is still a slight hum.

The slight hum disappears when i touch the strings, the tail, the jackplate, etc etc -- everything except the bridge. Is it possible the bridge is so cheap that it's not being grounded properly?
#13
The bridge can be insulated somehow via the paint or something. Apart from that everything seems to be right.
#14
Quote by Ace Carson
The bridge can be insulated somehow via the paint or something. Apart from that everything seems to be right.

The bridge appears to be painted black... Maybe i should replace it or scratch some paint off?
#15
Quote by scottythered
The bridge appears to be painted black... Maybe i should replace it or scratch some paint off?


If its definitely fully painted then you'll need to scrape some of the paint off from an inconspicuous spot and re-test.

So far it sounds like youre headed in the right direction if the remaining hum is only slight. Just a little bit more to go
Last edited by Phoenix V at Oct 5, 2011,