Ground buzz - Driving me crazy

[Littlewyan]

I have a very odd issue with my TW Express and Guitar. Its happened a few times now. When playing through my Express with my Gibson it sounds great. However if I turn the volume on the Gibson down to 0 then I get this buzz through the amp. The buzz stops if I unplug the guitar or if I turn the volume up a smidge. Right so its the guitar clearly. I then found that when touching the jack on my lead going into the guitar, it made no difference, as it shouldn't. If I touched the strings or the bridge, the buzz changed. Maybe the strings aren't grounded correctly?

Whats even stranger is I've only had this issue through my TW Express. Last night I swapped over to the Marshall and everything was fine. I checked the guitar today at home and I couldn't make that issue re occur through the Express. I've reseated the ground wire for the strings in my Gibson (2014 Classic so its a PCB) but I can't think what else it can be?!

[martin manning]

Maybe the strings aren't grounded correctly?

This, I think. Intermittently.

[Littlewyan]

Its the only thing that would explain it isn't it? I've just checked over the Express, all of the ground connections are and nothing is loose.

One thing I didn't check was the ground connection from the jack. The screws for the pickup height 'should' be grounded so if it occurs again I'll try touching them to see if they affect it. If so then it must be the ground from the jack socket is a bit loose.

[Colossal]

I had a similar issue with an R9. Poor QC. Any other guitar I had was dead quiet through my Express.

[Littlewyan]

What was the issue? Bad string/bridge ground? Or bad ground connection to the jack?

[Colossal]

What was the issue? Bad string/bridge ground? Or bad ground connection to the jack?

I don't know man, sorry. I didn't solve it, I sold it.

[Rober Medvesek]

What about with nothing plugged in? Do you have the hot lug of the input jack on the amp connected to ground if nothing is plugged in? And if not then plug in a cable (without guitar) and short the hot and ground on the other side of the cable. Do you get the buzzing? If yes the problem is in the amp not the guitar.

[pdf64]

Is there a grid stopper on the input stage (Trainwrecks tend to do without)?
If not, the buzz may be related to that, eg ultrasonic oscillation.
A 10k grid stopper should settle it, one way or the other.

[Littlewyan]

The jack shorts to ground when nothing is plugged in and the amp is dead quiet when that happens. I also plugged in a cable, shorted the tip to ground and the amp was quiet.

Grid stopper shouldn't make a difference as when the volume pot is on zero the input is effectively grounded.

[Littlewyan]

Found something! I looked at the boost circuit in the guitar and the battery has a permenant connection to the ground on the jack tip. With this guitar I find that when I have the volumes at zero if I turn the boost on then there is extra noise. I wonder if the issue is the boost circuit for some reason partly turns on or sometimes something is shorted within it. Anyway what I'll do is if it reoccurs I'll remove the battery. That way it should only be the pickups connected to the jack.

It'll be annoying if it is the boost as I never use it and would rather not have it! Shame as everything else about this guitar is great.

[pdf64]

I also plugged in a cable, shorted the tip to ground and the amp was quiet

Did you connect the tip to sleeve of the jack plug at the guitar end of the cable?
Or rather connect the jack plug tip to some other grounding point?

Grid stopper shouldn't make a difference as when the volume pot is on zero the input is effectively grounded.

Your analysis may be overlooking the parasitic capacitance, inductance and resistance of the instrument cable?
They may not be the cause of the problem here, but it's beneficial to bear in mind the effects of such parasitics when analysing any implemented circuit.

[Littlewyan]

I connected the tip to the sleeve at the guitar end of the cable on the same jack. So I was simulating the guitar being turned down to zero on the volume.

It has stopped randomly before and I tried moving the cable around, tapping the back of the guitar and the amp but couldn't make it come back! Don't you just love those kind of issues.

It is strange how last night when I moved onto the Marshall the buzz stopped. However it could be the Marshall is less prone to it as it does have grid stoppers and isn't as sensitive as the Express. It is a low level buzz compared to the level of the actual guitar. I wish I had time to move back onto the TW Express to see if the noise came back.

[Reeltarded]

I have had this problem happen when the ground is lifted because of a bad power cable or an incomplete outlet.

[pdf64]

I remember an issue a while ago where the bass player invested in a posh new planet waves instrument cable and got a buzzy interference at certain instrument vol / tone settings.
I checked the cable out and it was high quality, well made, low capacitance, and was fine at home.
But it still got the buzz the next band session.
I was all for him taking it back when I noticed that the buzz frequency changed when the portastudio was carrying out a function, eg got switched on, load/save a project, record.
I eventually traced it to a SMPS I was using for the portastudio; it must have been chucking out a strong EM field, whose frequency etc varied with the current draw from the portastudio.
The bass, being totally unscreened, picked it up, and his new cable was able to carry it, rather than dumping it to ground, which presumably is what the old cable had done.
That signal got detected at his amp's input stage, the result being the buzz.
A linear power supply for the portastudio resolved the issue.
But better filtering at his amp's input may have fixed it too.

[caps8419]

does it buzz more with your hand off the strings/bridge of your gibson? I presume yes as I have the same issues with my Les Paul on some amps. Gibson does a poor job of grounding the bridge. Much easier on a fender style. On same guitars they just don't even bother doing it... hit and miss I've found.