Ground buzz - Driving me crazy

[stretch2011]

I've had this same problem on my epiphone. Hands off the strings and it buzzed. I checked the ground on the bridge and it was connected. Got scary when I was getting small shocks in my hands when I was staying in a crappy old duplex.

Could be a bad ground on your guitar, could be a bad ground in your house.

[Littlewyan]

I've checked all the grounds in the amp and guitar and they're fine. I don't think it'll be a bad ground at the venue as my Marshall got plugged into the same power socket and was fine.

I get a slight buzz when the volume is up and I'm not holding the strings but I don't get any shocks off it. If you're getting shocks off it then that is pretty dam dangerous. People have died before when holding a guitar plugged into a badly grounded amp and touching a microphone or something that is grounded.

The buzz did change when I touched the bridge but not when I touched the jack socket. Strange as they are both supposed to be grounded to each other. Anyway I've reseated the ground cable into the PCB Connector for the bridge and haven't been able to make it happen again. I tested continuity between the jack's ground and everything else on the guitar and everything is fine.

I do wonder if the boost circuit was the cause somehow. As when I turn it on with the volumes down it does increase the noise. Probably because the battery is connected to the same ground as the jack and is injecting noise into the ground which is being picked up by the input stage.

Funny you should say that PDF64 as the other guitarist started bringing a different amp to practice and I do recall it started happening around then. Next time it occurs (if it occurs) I will get him to unplug his amp from the mains and will also remove the battery from my boost in my guitar to see if that stops it.

[pdf64]

Have you got any info on this boost circuit and how it's wired into your guitar?

[Littlewyan]

I don't unfortunately. All I know is the battery negative is hard wired to ground.

[Rober Medvesek]

Probably because the battery is connected to the same ground as the jack and is injecting noise into the ground which is being picked up by the input stage.

A battery is (or at least should be if wired correctly) the cleanest power you can get (pure DC) and as such should not inject noise. The boost amplification circuit is the noise source IMO. It is usual practice (at least what I've seen and implemented) that the battery negative pole is wired to the guitar jack so when the cable is unplugged you disconnect the supply from the boost thereby saving battery life.

Can you draw up a schematic of how the boost is connected to your guitar?

Kind regards,
Robert

[pdf64]

Is it wired in like a true bypass fx pedal, ie on a dpdt switch?
What devices are on the board? eg transistor, IC, gunk.

[Reeltarded]

POINT OF ORDER

GUITARS BUZZ WIth YOUR HANDS OFF THE STRINGS

THAT IS NORMAL AND HAS NOThING TO DO WIth BAD GROUNDING

Thanks/ Carry on.

[Littlewyan]

I'll take a look at the weekend if I can. From memory there is one Transistor. Not sure if its a dpdt switch, I think it is.

Reeltarded - Why is that? As the strings are grounded, so in theory I should be able to stop the buzz by touching the jack socket. Actually saying that, where does the ground for the strings connect to? In the Les Paul cavity you just see the cable disappear into the wood.

[katopan]

The sack of mostly water called your body is conductive and picks up all the EMF noise you'd like (or not). Put it in vicinity of the pickups by having the guitar in playing position and the pickups, well, pick it all up. By touching the bridge or strings you are grounding your body, which means the EMF your body is picking up is grounded to the same reference as the guitar, which means your body is now acting as a conductive shield rather than a conductive antenna.

Simple test: compare guitar in playing position without touching the strings, guitar totally away from your body, playing position with touching strings. They should be most to least noisy, with the stand-out worse being the first.

Touching the jack negative with a small area of a finger isn't as effective as the more contact you get with touching the strings. Becomes even more effective if you touch the strings and bridge with both hands. The bridge wire connects to the controls ground and should go through to the jack ground.

[stretch2011]

Oh I understand the consequences of bad grounding. I did say crappy apartment right? Looked inside the wall outlet......no ground connected. Needless to say I didn't stay there long

[Littlewyan]

God dam, its amazing there are still places that badly wired. Least you weren't hurt.

Sorry Katopan that doesn't make much sense. If I touch the bridge with the tip of my finger it stops buzzing, touch the jack and nothing happens. Plus the strings and jack are supposed to be grounded together. Plus plus don't forget I've got the volume on 0 when this happens and its intermittent.

Altho I haven't been able to make the issue re occur at home so far. Not since reseating that ground wire. I did find some plaster thin covering left on the bridge/strings ground wire, but I don't think the covering went into the connector as well. Either way I removed it as it was flaking off anyway. I should explain, the PCB connector for the ground wire is one you clamp onto the wire and the wire is solid.

[Reeltarded]

If you touch the plug you still have buzz, but not when you touch the strings? The ground wire goes to a tail stud or a bridge stud. The instrument will buzz all day with stings off.

Once you are common with the shield, unless you are using single coils or in a place full of lighting ballasts, it should be silent-ish.

If you can touch the plug only and it doesn't act exactly like touching the strings, the problem is the jack has an improper ground.

[dorrisant]

Test for continuity between the bridge of the guitar and the output jack ground?

[katopan]

Yeah, they should certainly have the same effect because they should be connected.

[Littlewyan]

Ok so I had band practice on Thursday night and this time there was noise but nowhere near as much. Also this time it changed when I touched both the strings, the jack and the case of my attenuator. So it must be something injecting interference into the earth in that room. The Express is so sensitive its obviously more prone to picking up the noise whereas the Marshall isn't. Its a similar noise to the one my wireless printer makes when I play in the room with it plugged in. Even with the printer off it still generates a lot of noise.

Anyway maybe last time the connection between the strings and jack ground wasn't good which made it worse and I solved that by reseating the wire. I'll keep an eye on it.

I've seen some guys use some kind of AC Filter build into the power socket in their amps. What is that for?