Need help fixing a ground problem with my axe

[wickerman]

I've been trying to shield my Flying-V using copper foil in the cavity and 'star-grounding' but I must have a ground loop or something somewhere as my guitar buzzes loudly when the volume control is turned down -- until I touch the strings or metal parts. (The buzz gets louder if I touch the body of the guitar but not the metal.) The wiring includes a bridge ground wire. This and all the pickup grounds and shields go to a screw driven into the shielded cavity. The ground lugs on the pots have been disconnected from the circuit.

I've been playing around for hours with a multimeter and a pair of crocodile clip connectors but I'm still left scratching my head. Can anyone help?

[wickerman]

Something else I should mention... Both pots are wired as volume controls for the pickups. The circuit works fine but for the noise.

I've been re-reading the Strat shielding instructions and it says the "star" ground should be insulated from the copper shield. So I tried removing the screw and attached all the ground wires to a washer which did not touch any other part of the circuit. No change.

I've gone about as far as I can with this problem now and I'm just about ready to take it to a professional to get it sorted. Can anyone save me a few bucks by helping me out?

[UnklMickey]

wickerman said:

Something else I should mention... Both pots are wired as volume controls for the pickups. The circuit works fine but for the noise....

wickerman said:

...The ground lugs on the pots have been disconnected from the circuit...

this might be the problem, or it might be making a small problem worse.

this would prevent one volume being turned all the way down from killing the signal from the other.

but, it also leaves the output virtually open when neither pickup is on.

although it can be annoying, wiring the pots "normally", gets rid of the noise when off.

you just have to be careful to not turn a volume to zero when both pickups are selected.

i can't quite wrap my mind around why touching the body would make the noise louder, though.

[wickerman]

Thanks. Obviously I'm avoiding rewiring the pots the 'normal' way for the moment since this would presumably negate all the effort in trying to shield the cavity.

Can anyone clarify whether or not the star grounding point should be in contact with the foil shield?

[hammeroff]

I think the original Quieting the Beast mod has all the grounds going to the back of a pot. So, I guess that would put them in contact with the copper shielding before it goes to the actual ground wire connected to the bridge & strings. I don't think that makes a difference though.

The first time I did the QTB mod, that's how I had it, (all the grounds to the back of a pot) and it worked fine, but that was just stock Stratocaster wiring; I've never tried to wire up a guitar similar to how your Flying-V is

Here's a good article, it helped clear some things up for me:

[UnklMickey]

well, that all depends on what you mean by ground "lugs"!

if you mean the case (back) of the pots, then disconnecting those will not cause a problem.

but if you mean the CCW tab (your pot has 3 tabs), disconnecting that IS a problem.

so are all 3 tabs of the pots connected to something?

[wickerman]

The QTB instructions say to disconnect the ground tab on each pot from the pot casing (where it normally gets bent back and soldered) and instead wire the output jack ground directly to this; then to wire this point to the star terminal. I tried this but it didn't fix the noise when the volume pot was turned down.

[wickerman]

hammeroff said:

Here's a good article, it helped clear some things up for me:

I read this but it didn't help with my issue.

[UnklMickey]

okay, so you do have a connection from the ground tab of the pot to the star ground. good.

next question are your volume controls wired "backward"? that is, are the tabs that connect to the output on the outside of the 3 tabs? or is the output taken from the center tabs of the controls?

[wickerman]

The pickup hot wires are wired to the centre tab on each pot.

[UnklMickey]

okay Wickerman, that's probably why you are having the problem.

that does, is keep the volume controls independent.

but, the price you pay, is the noise when the volumes are at minimum.

decide which is more important. noise when volumes at minimum, or completely independent volume controls.

[wickerman]

I can't do this and fully shield it? What's the alternative -- wire the second pot as a tone control? What would happen if I just wired the grounds to the back of the pots as normal? I guess keeping it quiet is what I want most.

So should the star ground point be isolated from the shield or connected to it? I still don't get this part.

BTW, I just tried connecting it back up using crocodile clip cables (second pot as tone control with ground tab going to the star ground) and it was still noisy with the pots rolled down.

[UnklMickey]

i think the problem is with the pickups being connected to the wipers.

sheilding or no shielding, this is gonna be noisy when the volumes are turned down.

the reason the starground and the shield ground are separate, is for the capacitor to protect against DC shock.

if you aren't going to use that cap, you can just tie the star ground and shield ground together.

[wickerman]

I wonder if it would make any difference if I reversed the position of the in and out wires on the pot?

[wickerman]

I've done it! Or at least I've got it functioning how I wanted with the minimum amount of noise. Both controls wired as volume, but I reversed the input and output wires on each pot. The rest is wired as instructed in QTB. There's a very small amount of buzz when I take my hands off the strings but I can live with it.