Ground control for Major Tom....?

[BloodRose]

My US Charvel hums like a banshee unless I touch the strings, one of the volume knobs, or the three way toggle (other than the plastic tip).. Im pretty sure this must be a ground issue.. I didnt believe this, but I once had a guitar tech tell me that that is normal on a guitar wired properly for it to hum unless you are touching something. That didnt sound right to me. Also, the guitar I had ask him about, the hum would go away once I started to play. This one I can still hear it.
The config for the guitar is Hum/hum, controls are Volume/volume , 3 way toggle. (though I may one day change to volume/tone/ 3 way) Anyhow, I checked all the wiring. All solder joints are connected and seem secure. (was afraid something had come loose). And, Im pretty sure it didnt hum when I first switched out the bridge pup. I noticed last night that it still seems to hum when being played too, even though the sound of the playing pretty much drowns it out.

Suggestions?? Thanks!

 

[PFDarkside]

Re: Ground control for Major Tom....?

Is the bridge ground still connected/making contact?

 

[Darg1911]

Re: Ground control for Major Tom....?

Just went through this with an HH Godin. The bridge ground was good. They didn't use shielded wire for most of the switch cavity to the control cavity nor inside the control cavity, from pot to pot. Only from switch to jack was shielded wire. The guitar has conductive plastic pots with circuit boards. I love the feel and taper of those pots and put off running shielded wire for a long time. The wires are soldered to pads on the pcb's, they aren't through hole, so rewiring to the pots would be a pain in the arse. But, I finally had enough of the buzz and swapped the pots out for Bourns mini's and ran all shielded wire. That helped a good deal but still buzzed more than it should have.

I decided to give carbon (graphite) shielding paint a go. So, I pulled it apart again and painted both switch cavities and the pick-up cavities with the shielding paint. 2 coats total. I also wanted to try and use the stock pots again. I drilled the solder pads so I could feed the wires through-hole and solder. That worked fine because the pads were large enough and the traces under the solder mask are larger than the pads. I wired it up again with shielded and it's about as dead quiet as it gets now.

I really was skeptical because I wasn't able to completely coat the wiring channels between the two pickup cavities and between the pickup cavities and the switch and pot cavities. I didn't have any way to reach in and do the tops of those channels thoroughly so I just did the best I could but I made sure that the paint was continuous along the bottom of those channels. I ended up with about 2 ohms checking resistance from the switch cavity to the main control cavity when the paint was dry. Also, I glued some heavy aluminum foil to the bottoms of the cavity cover plates. That makes contact with the shielding paint when they are screwed down.

It wasn't a hard job, just a little time consuming. I had never resorted to shielding a guitar before. I have always owned humbucker guitars, and rarely a single coil guitar, here and there. My Korean imports cavities all have a coat of shielding paint from the factory. Maybe that explains why they are all quiet. The Gibsons I've had were always quiet too (or quiet enough not to worry about). Not sure why this Godin was so buzzy but, problem solved. Also, if there is any change in the tone, it's too subtle to notice. I thought I may have heard a little bit difference after I swapped to shielded wire, maybe. But nothing further after shielding the cavities.

If you don't want to read the book I just wrote, I'll simplify it by saying ... consider shielding the cavities with paint or copper foil/tape. I bought 2oz of shielding paint off of ebay (I think it was 14 bucks). It's the only guitar I needed to do and I didn't want to spend 30+ bucks plus shipping on the stuff at Stew Mac.

Sorry for the book but I wanted to be thorough. I guess I could have still left out the details about the pots.

 

[BloodRose]

Re: Ground control for Major Tom....?

oK, let me try this again.. I keyed everything that Im about to key here on my phone last night and got caught the login expired loop and lost it. %$!#!@$!$

First, thank you PFDarkside! Ill check into that. Everything I saw in the cavity looked good, but didnt check the trem.
Darg1911, Thanks for all the info.. didnt mind the detail.. Found it informative. Sounds like a very frustrating sitch and glad you got to the bottom of it. Such a simple thing in the end.. thats what scares me about all these new axes with all the electronic gadgets. Makes troubleshooting and fixing a nightmare. I keep saying I need to get some shielding paint and shield my guits. I just shudder at the idea of gutting them to do it..

Some other info I wanted to add about what mine is doing, from playing it last night. The one guitar I had that the tech told me was normal, was noisy and when I touched the strings, went dead silent. This one, if I touch the strings or knobs, it gets quieter, but still is noisy. And, I can still hear the noise when playing.

Crap.. there was another thing I wanted to mention and I cant think of it now... Last night I had a bunch more.. Anyhow, thanks for the input so far.

 

[BloodRose]

Re: Ground control for Major Tom....?

More info.. Sorry, not trying to flog this horse, just trying to be precise as I can to narrow down the problem.. Ok, last night I was alittle less exhausted than I usually am when I sit down to play, so I got a clearer perspective.

First, I looked at the ground on the trem. Very secure.. I have the KGC Brass claw and that has the connector screwed to it and the crimp is tight and screw is secure. Have four raw vintage springs and a large brass block.
Ok, when the pots are FULL ON, NO hum.. Any where thru the sweep, hum. And its all three toggle positions. If toggle is on neck pup, the hum is present thru the sweep of the front volume knob. Doesnt matter where the back vol knob is. vice versa for the toggle in back pos. So the toggle is disabling things as it should. I did notice some noise in the pots (CTS500k) during rotation, so will clean them

 

[Darg1911]

Re: Ground control for Major Tom....?

oK, let me try this again.. I keyed everything that Im about to key here on my phone last night and got caught the login expired loop and lost it. %$!#!@$!$

First, thank you PFDarkside! Ill check into that. Everything I saw in the cavity looked good, but didnt check the trem.
Darg1911, Thanks for all the info.. didnt mind the detail.. Found it informative. Sounds like a very frustrating sitch and glad you got to the bottom of it. Such a simple thing in the end.. thats what scares me about all these new axes with all the electronic gadgets. Makes troubleshooting and fixing a nightmare. I keep saying I need to get some shielding paint and shield my guits. I just shudder at the idea of gutting them to do it..

Some other info I wanted to add about what mine is doing, from playing it last night. The one guitar I had that the tech told me was normal, was noisy and when I touched the strings, went dead silent. This one, if I touch the strings or knobs, it gets quieter, but still is noisy. And, I can still hear the noise when playing.

Crap.. there was another thing I wanted to mention and I cant think of it now... Last night I had a bunch more.. Anyhow, thanks for the input so far.

The Godin got quieter the closer to the bridge I was playing. But while playing anywhere on the neck, it wasn't buzzing enough to matter. For example, if I was just checking the buzz (because it was driving me nuts), and I fretted a power chord or single string at 2nd or 3rd fret, I could still notice some buzz. If I barred the 3rd fret, no buzz. If I fretted at the 15th, even a single note, I couldn't, or at least it was much less.

One last thing. I don't know the technicality of it all, maybe it's basically the same cause. But when I say buzz, I'm talking about buzz more like the sound of a swarm of "bees", not the sound typically associated with something like 60 cycle hum like you may hear with an old amp that needs the old electrolytic filter caps replaced.

 

[devastone]

Re: Ground control for Major Tom....?

You can get shielding paint from GFS - http://www.guitarfetish.com/XGP-Flat-Black-Cavity-Shielding-paint-HIGHLY-conductive_p_18783.html

You'll need to put copper tape on the back of the covers too, and make sure that it makes contact with the paint, i.e. you'll need to paint over the edges all the way around so the foil and paint contact all around the cavity. Also make sure there is good ground connection to the paint, which there should be through the body of the pots. Although, the fact that it doesn't hum when the volume pot is full on, but does when you turn it down leads me to believe there may be something else going on in the wiring. Do you have a meter that you can check the ground points with?

And, with all of that, there are still electrical holes and no guarantee you can get rid of all the hum.

 

[BloodRose]

Re: Ground control for Major Tom....?

Thanks.. Funny twist to this situation. Plugged into my splawn and no hum, only when I use my headphone amp and no other guitars do that. ??? Im still gonna lube the pots and shield it tho. playing wise, im not ready to gig, but instead of buying more guitars, Im getting my guits and board and everything ready for when I can..

 

[PFDarkside]

Re: Ground control for Major Tom....?

Ah, seems like the Splawn provides a proper ground through the chassis, the headphone amp may not be.

 

[BloodRose]

Re: Ground control for Major Tom....?

yeah looks that way.. Funny, never had any others respond this way.. Im gonna keep experimenting. (will try it with my Classic 30 once I get the preamp tubes replaced) Want to make sure its the headphone amp and not the guitar. hate to have any surprises if I jam with someone or something..