Classic Grounding Question: Hum Goes Away When I Touch Strings

[Cactus Jack]

The guitar is a rear route Strat with 3 single coils. The pickups sound great, and I'm very happy with the tone. However, if I'm not touching the strings, or other metal, the guitar pickups up significant hum beyond the expected 60 cycle hum. When I do touch the strings everything sounds like it should and I get the 60 cycle hum in positions 1,3,5, and it's dead quiet in 2, and 4. Remove my hand and I have loud hum in all positions.

Using a multimeter I have a clear signal from the output jack to the strings, between all three pots, I even grounded the switch since there is no pickguard. I'm sure what else to check. Any thoughts?

 

[guitarstv]

Did you ground the bridge?

 

[Cactus Jack]

Yep. Bridge to output jack, pots, switch, all near perfect continuity.

 

[Cactus Jack]

Here's a pic of my harness:

Here's the original diagram:

The switch and all controls work perfectly. The pickups are wired properly and sound great. I just can't get rid of this additional ground noise.

In an attempt to fix this I have: Grounded the lug on the blender pot to the casing. I ran a jumper connecting all three pots, and I grounded the switch to the volume pot.

 

[ragamuffin]

Doesn't that happen with every guitar to some degree?  :icon_scratch:

 

[drewfx]

Are you sure your ground is connected to ground? You don't want to be the ground connection.

 

[Cactus Jack]

Doesn't that happen with every guitar to some degree?  :icon_scratch:

It does, but not like this. I'm getting above and beyond what is normal and expected.

 

[Cactus Jack]

Are you sure your ground is connected to ground? You don't want to be the ground connection.

Something is the circuit is open, I'm just not sure what. The bridge, pickups, switch, jack, and pots are all grounded to the back of the volume pot. What else is there?

 

[drewfx]

What else is there?

Everything outside the guitar, starting with the cable.

 

[Cactus Jack]

I quadruple checked my solder joints and I get excellent continuity, but still get a crap ton of extra hum and buzz. I'm going to bust out the copper tape and shield the cavity. Hopefully that does the trick.

 

[Cactus Jack]

I shielded and grounded the cavity with copper tape. There is no meaningful improvement. Guitar plays and sounds great, but the additional buzz really robs the joy of jamming with it. Back to the drawing board.

 

[Cactus Jack]

Here's a pic of the cavity. Since the cavity is lined and everything is grounded to the volume pot I removed all the jumpers. I get perfect, 000 ohms, continuity readings between all components. The largest variance I got was 001 between the output jack and the G string. Again, the guitar sounds great, but the buzz has me begging for 60 cycle hum!

 

[VinceClortho]

Sounds like you've got the guitar done up as good as it can be.  Have you tried a different cable and/or ruled out other EMI sources?

 

[Rick]

Power conditioner at the amp? Tried another venue? Battery powered amp? Power conditioner for any pedals?

 

[Cactus Jack]

Problem solved!

After shielding the control cavity with no success I decided to pull the pups and shield those cavities too. Figured I'd might as well do it all since I had the tape handy. I got the copper in place, ran ground wires back to the main cavity, and soldered everything up. During the process I also grounded the metal pickup rings for good measure. I checked continuity across all cavities, rechecked every single connection. Bingo, bango, bongo!

Quiet as a church mouse. Wonderful 60 cycle hum where's it supposed to be, and dead quiet every where else. Oh, the wonders of guitar electronics. So deceptively simply and dastardly frustrating.

 

[BroccoliRob]

Doesn't that happen with every guitar to some degree?  :icon_scratch:

Yae , this is how every single coil only guitar ive ever owned has been except for my noiseless Injectors