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26 December 2014

How to ground an electric bass guitar

It's been a while since I've done a "How to" post. Today I remedy this as I try to fix my ailing bass guitar...

I borrowed this guitar about 8 years ago from an old school friend. It belonged to his brother who has never asked for it back  :-D

It's a full-size Hohner Rockwood LX90B and is a fairly true copy of the original Fender Precision Bass it is modelled after. The difference is that the Rockwood (if you can find them anymore) retails at about a tenth of the price of the Fenders.

"My" one has a number of issues including the fact that the machine heads rattle when played. You can see above that I've taped them to stop it. The biggest problem however is a grounding issue which seems to be getting worse. This week I've had a go at fixing this problem, so It seems only right that I share some of my adventures with you.

The grounding issue I originally had was the typical problem of the bass producing a clicking sound whenever I touched anything metal. I can and have lived with this problem since I got it, but over time I've noticed that a buzzing noise has appeared. It has caused me all sorts of problems on my recent recording collaboration and this is the main driver for me finally decided to do something about it.

My first foray into sorting it out was pretty much a tentative exploratory look inside and a chance to clean up the bass. I don't think this bass can have been cleaned since it was bought! The fretboard had ridges of grime that took an age to wipe off! Yuck!

The strings are just rusty wire. I want to stick some Elixirs on, but there's no point doing this if I can't sort out the grounding issue first.

I was keen to check under the bridge to see what the state of the grounding was. Here you can see that it is pretty flimsy, so I added in a second fresh wire. The general idea here is that there needs to be a connection between the main electrics and the strings and this is usually done by running a line from the tone pot ground to the metal bridge.

If this was a problem, it certainly didn't fix the buzzing.

It was about this time that I realised that I needed to be a bit more scientific with my trouble-shooting. Out came the multimeter and I couldn't for the life of me remember how to use it.

Digging back through my archives on this blog I found the post where I was wiring up my Kingcaster Electric Ukulele. I learnt so much doing that build... including how to tackle grounding issues.

What I needed to know was how to check for continuity in the circuit. If there were breaks in the circuit then this might be causing the buzzing. The picture above shows you how to set up the multimeter to check continuity. All you do is to touch the two places with the prongs that you want to check and if there is a circuit then the continuity buzzer will sound. Silence means that you've got a problem.

I went through the whole circuit and to the best of my knowledge, everything looked good

Next stop was to add some copper foil around the insides of the body cavity. I've joined it all together via a strip that will run under the pick guard. The connection to the main circuit is by touching the original silver foil stuck  on the underside of the pick guard.

Here's a shot of the wiring in the Rockwood. There seem to be a number of different configurations for actual p-basses, and I don't think I found one with this exact configuration.

There are two linear 250k pots. These both crackle when I turn them, so they might be worth replacing in the longer term.

I know this is probably irrelevant, but you can see that I added a small connection from the ground on each pot to the pot cases themselves (the little lengths of black wire). You see this a lot with pots fitted to electric guitars so I wondered if it might help here. In order to get this to work, I had to scrape a sort of coating that was on the pot casing in order to allow a connection and for the solder to take.

You can also see the two wires from the tone pot that leads to the bridge; The original and the new one I added. I do wonder why this connects to the tone pot ground and not direct to the jack socket ground. I was tempted to experiment here, but never did in the end.

Here's it all put back together again. You can see that I've been sloppy and got some foil sticking out from under the pick guard. I've also screwed the pickups down flush with the pick guard to add a bit more space between the strings and the poles.

Did it work?

Yes and no.

There is no longer a buzz! Yay!

There is a slight click though in certain settings. If I have the Tone fully down and the Volume fully up then it is perfect - no buzz or clicks. As I turn up the Tone then the clicks starts to appear as I touch the metal. Either way, the buzz has been beaten! Ha ha!

I wish I knew which of my many little tweaks made the difference. ;-)

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