guitar hum

[tempus]

Hey all;

Not exactly a stompbox question, but I'm sure lots of other players may have this problem too. My amp is virtually hum free, but my guitars (Gibson SG, Gibson Explorer, and a homebrew) all hum. When I touch any metal part of the guitar(s), the humming decreases significantly. I should point out that the hum is not unbearable, but is noticeable, especially when I touch a metal part and it goes away. If I plug into my pedalboard and add any high gain effects, the hum gets insane.

I've considered doing some of the shielding suggestions from guitarnut, but all the wiring inside the guitars is already heavily shielded. And how am I providing a better path to ground than the ground wire (shield) in the cable?  Does anyone else have this problem? Any suggestions as to how to deal with it?

Thanks

[Paul Marossy]

Could be an environmental problem. If you have a lot of wall wart transformers around, they can radiate enough EMI to where even a humbucker will pick up some of it, and high gain pedals will amplify that to where it's very noticeable. Also, if you have floating grounds anywhere in your system, that will create an environment where you have a lot of noise in your audio system.

You might find this video interesting: http://www.youtube.com/watch?v=6ZGokkrsO_Y

I bought that low voltage detector in the video to figure out some of these weird situations you can get where in theory you shouldn't have any problems but do.

Anyway, in today's world, from the bare (not in a metallic conduit) "Romex" AC wires running around in our homes we constantly have about 10-12 VAC imposed on our bodies through capacitive coupling and our guitars, pedals, cords, etc. all want to pick up that noise and inject it into our system. Add to that any floating grounds and things can get crazy real fast in terms of audio noise.

[petemoore]

  SHielding 'can help, as can every other layer of the onion that must be peeled to get at the 1 or more layers that are making the peeler cry.
   Excellent guitar cable tried ? [the one you have is probabably fine and very good, worth a check though, HB's tend to cancel hum...shielding 'might' help...
   Before all that though, investigate what Paul said about WW's, Gnd. loops...these power and ground supply situations vary, we don't know what you have there.
   Lifting all the 'other' grounds [using floating/regulated power supplies] except the signal ground wire through the guitar cables did wonders for allowing me to find/eliminate 'all' noise..keeping the signal path purely guitar signal path isn't possible, but getting as close as possible has to be good enough.

[tempus]

Thanks for the replies. Paul, I found this when I was checking out the link you sent:

Guitars hum when they're plugged in as they pick up EMI/RFI, but grounding the human usually makes some of the hum go away, as the human's body provides some degree of shielding. This is normal, and is the reason that guitar makers install a ground wire to the bridge. So hearing a reduction in hum when you touch the bridge is normal and expected. However, if you have excessive hum, then maybe something isn't connected properly, or you have a poor ground connection somewhere.

That's from Acme Guitar Works - sounds reasonable, except for the human shielding thing.

Also, Pete, your suggestion about lifting all other grounds is good, but I'm talking about a guitar straight into an amp - no pedals wall warts or nuthin'. I'm beginning to lean towards the environmental explanation, but if there's something I can do to lessen or eliminate this little annoyance, I'd be glad to know what it is.

[fuzzy645]

Hey all;

Not exactly a stompbox question, but I'm sure lots of other players may have this problem too. My amp is virtually hum free, but my guitars (Gibson SG, Gibson Explorer, and a homebrew) all hum. When I touch any metal part of the guitar(s), the humming decreases significantly. I should point out that the hum is not unbearable, but is noticeable, especially when I touch a metal part and it goes away. If I plug into my pedalboard and add any high gain effects, the hum gets insane.

I've considered doing some of the shielding suggestions from guitarnut, but all the wiring inside the guitars is already heavily shielded. And how am I providing a better path to ground than the ground wire (shield) in the cable?  Does anyone else have this problem? Any suggestions as to how to deal with it?

Thanks

All guitars do this when the bridge is grounded.   With a bridge ground in place, as soon as your body touches the strings your body essentially becomes part of the ground.  You can have any one of your buddies show up with their guitar and it will do the exact same thing. I have never met a guitar that does not do this to some degree.

Shielding will help minimize the noise to begin with, but there will always be a difference "hands up" vs. "hands down" when the bridge is grounded.   

Now, if you choose to not ground your bridge, the instrument will be noisier all the time, but there will be no difference between hands up vs. hands down. 

[Puguglybonehead]

I know you may have already checked this in the "environmental" conditions, but, is there any fluorescent lighting where you're playing? This would even include compact fluorescent bulbs. I've usually found lighting to be a major culprit when it comes to hum. Another thing I found, my cellphone. I've since started shutting it off, or not wearing it when I play.

[ashcat_lt]

The wires are shielded, good.  Are you sure about the wires that run up to the switch and back?  These sometimes aren't.  Also, what about all the other components?  The switch, the pot lugs, and the sections of wire which must be stripped back before they're soldered.  These are all chinks in the armor, and the buzz will find its way in.  Shielding the control cavities might help.

Edit to add -  I have met guitars which did not get quieter or even got louder when the strings were touched, but they were wired wrong. 

[petemoore]

I'm talking about a guitar straight into an amp
  Try without the guitar, without the cable...or just ground the pickup output [switch to 1 pickup, then turn its volume control to 0] to test if theres a hum being generated in the amp..

[tempus]

Thanks again for your reply Pete, but

My amp is virtually hum free,

[Paul Marossy]

Shielding will help minimize the noise to begin with, but there will always be a difference "hands up" vs. "hands down" when the bridge is grounded.  

Now, if you choose to not ground your bridge, the instrument will be noisier all the time, but there will be no difference between hands up vs. hands down.  

Yeah, and then because there is no bridge ground your body becomes a path to ground in the event of some ground failure in your amp, which can be potentially fatal. I myself would rather live with a little bit of noise.

EDIT: Or if I was bent on not having the bridge grounded, I would get some pickups like EMGs that don't require the bridge to be grounded.

[fuzzy645]

Shielding will help minimize the noise to begin with, but there will always be a difference "hands up" vs. "hands down" when the bridge is grounded.  

Now, if you choose to not ground your bridge, the instrument will be noisier all the time, but there will be no difference between hands up vs. hands down.  

Yeah, and then because there is no bridge ground your body becomes a path to ground in the event of some ground failure in your amp, which can be potentially fatal. I myself would rather live with a little bit of noise.

Actually its the opposite. If the bridge IS grounded, and your body touches the strings, then there is a  chance you will get a shock and a slim chance you will get a fatal shock.  The guitar nuts site has some kind of fix posted with a large cap in the bridge ground path to (hopefully) eat up some of that voltage.

The safest (but noisiest) approach is to NOT ground your bridge.  Then and only then will there be a guarantee that your body can not be part of the path to ground.  In this case, touching the strings will be equivalent to touching the wood as the strings are not electrically connected to the circuit at all.

Either way in the year 2011 I wouldn't worry about it too much, unless you are a pretty active gigging musician who might play some halls with sub-standard house wiring.  For a guy playing in their living room the chance of getting such a shock is slim to none.

[Paul Marossy]

Actually its the opposite. If the bridge IS grounded, and your body touches the strings, then there is a  chance you will get a shock and a slim chance you will get a fatal shock.  The guitar nuts site has some kind of fix posted with a large cap in the bridge ground path to (hopefully) eat up some of that voltage.

Either way in the year 2011 I wouldn't worry about it too much, unless you are a pretty active gigging musician who might play some halls with sub-standard house wiring.  For a guy playing in their living room the chance of getting such a shock is slim to none.

I don't agree that it's safer. "Death caps" in old amps were not much of a safety device. Besides, your controls are still grounded. Touch the controls with metal knobs on them or your output jack and you are touching ground.

There are still some old houses with jacked up wiring. NEVER assume that the electrical wiring is safe everywhere, it's just not. Unless you have GFCI circuits where you are plugged in, you could still be at risk with any kind of ground fault. A regular breaker would not trip fast enough. If there are grounding problems in a system, it's always best to find the source of the problem and eliminate in a safe way than trying to do a dangerous ground lift everything bandaid approach.

[fuzzy645]

OK, I will agree with that....touching our jack or knobs will connect you to ground.

What I don't understand is why would grounding your bridge provide any safety?  All it provides is one extra place for you to touch ground.

[arawn]

check for ground loops in the guitar wiring, they will literally act like antenna's drawing in the interference

[ashcat_lt]

The safest way to avoid shocks is to go wireless.  Then there's just no way for high voltage to reach the guitar.  Next best is to make sure that the amp and the outlet to which it's plugged are wired properly.  The "safety cap" from GuitarNuts might help keep the one uncommon fault that puts high V DC on the chassis from killing you.  It won't stop the far more common AC leakage current.

The GuitarNuts site also makes a pretty big deal about star grounding, but most of us on the GN2 forum discount the importance.  Heck, even in stompboxes we don't generally worry much about internal ground loops!  I've seen number of people report buzzing after shielding and star grounding a guitar which was only improved when the wires between the backs of the pots (the cause of the ground loop according to Mr. Atchley) were replaced.  Yes, creating a ground loop reduced the noise.  [shrug]