grounding issue

jimistone

jimistone

long standing member
I've been playing some guitar in the tube amp I just bought and I noticed some loud hum when I'm on the ultra gain channel. I can touch the metal jack cover on either end of the guitar cord and it silences it. I'm playing a strategy through it and I realize there will be some 60 cycle hum but touching the end of the guitar cord won't silence 60 cycle hum. I haven't noticed it because it's barely audible on the clean channel and the gain channel. Barely audible but still there on those channels too. Touch the end of the cord and it goes away. Also, unplug the guitar from the amp and its silent.
Does that sound like an issue with the guitar or the amp?
 
Um, I think that's a guitar issue. Make sure your bridge ground wire is actually connected to something that grounds through the cable, through the amp, to ground.
 
OK thanks. When the pickup on my old strat died a few weeks ago, and I put a temporary replacement in, I probably made a bad ground solder joint.
 
When you touch the bridge does the hum go away? What pickup did you put in ?

Trying to figure out what, if anything on the guitar is causing it. Sometimes with strats and high gain, the high gain will magnify the noise. Noise that wasn't that noticeable before.
Some pups also have a higher (or lower) signal to noise ratio. But as you already know being a strat guy, all single coils buzz and hum.
 
Ok, but does it go away when your hand is touching the bridge? Or only when you touch the metal sleeve of the jack?
 
I dunno, I'll check it out when I get back home tonight. It could be the cord. I'll try another.
 
Greg_L said:
Um, I think that's a guitar issue. Make sure your bridge ground wire is actually connected to something that grounds through the cable, through the amp, to ground.
Click to expand...

Exactly. Just went through this with a guitar...ground wire to pickup/cover is most likely the issue.
 
I'm having grounding issues as well with one of my guitars. No surprise, it's the one that I did my first (and only) pickup replacement. Actually, I gutted all of the old electronics and replaced them (new pots, caps, etc). I typically play with a lot of distortion, and now there's only about a 10dB difference between the noise and my signal. I checked my wiring. there's nothing loose or hanging.
When I touch any of my hardware the noise goes away, except, for when I touch my bridge pickup. It actually adds to the noise.
 
Being that you gutted and replaced the electronics...I would look to everything you touched.
Did you miss something...are all the solder joints good...the the bridge ground wire get disconnected, and are all the pots connected with a common ground wire...etc.
 
I had a lot of buzz on my homebuilt bass when I finished it. I fixed it by adding a ground wire to the bridge. Turned out to be a pretty important little detail. Maybe during your rework, you didn't reconnect the ground wire.
 
I am always concerned when someone has hum (aka "grounding/earthing") problems AND they tend to go away when metal is touched!

This CAN indicate that the amplifier has lost is own mains earth (grnd) and is thus not only noisy but positively dangerous* .

OP. You swapped out all the guitar electronics? Not I hope without the use of a digital testmeter? Of course not! So, grab the meter and set it to "Ohms" and check the continuity between the earth pin of the mains cable and the chassis and jack sleeve. Should read very low, less than one Ohm. If open circuit try another mains cable if IEC type otherwise get the amp to a tech'.

You can also check for low readings on the bits on the guitar already mentioned.

*Sometimes peeps disconnect mains earths in a misguided attempt to fix ground loop problems. Often it works but leaves the gear potentially lethal... DO NOT DO IT!

Dave.
 
So, as far as I can tell, my connections are all solid. Although, I'm not very good at soldering. Most of my solder joints are cold. They have that dull, matte finish. Would that have an affect on anything?
 
HRmusic90 said:
So, as far as I can tell, my connections are all solid. Although, I'm not very good at soldering. Most of my solder joints are cold. They have that dull, matte finish. Would that have an affect on anything?
Click to expand...

Absolutely.

Soldering on to the backs of the pots is probably the hardest bit so get them really hot with the iron first and make sure they're flux-clean.
That should help.

If the solder isn't flowing on to the back of the pot all nice, don't put the wire near it. :)

When you're soldering anything, prep both surfaces first. Clean them manually if applicable, heat them, flux them, tin them, then join them.
 
I don't even bother soldering to pots. The ultimate ground in a guitar is the jack sleeve. Pot bodies are only connected for shielding purposes. If they are not already connected some other way (like by touching the shield foil in the cavity which is also connected to ground some other way), then I'll solder a wire to washer slipped over the shaft.

HRm90 - What part of the bridge pickup are you touching when it gets noisier? Does it have metal cover, or are you touching the pole pieces?
 
ashcat_lt said:
I don't even bother soldering to pots. The ultimate ground in a guitar is the jack sleeve. Pot bodies are only connected for shielding purposes. If they are not already connected some other way (like by touching the shield foil in the cavity which is also connected to ground some other way), then I'll solder a wire to washer slipped over the shaft.
Click to expand...


I too dislike using pot cans for earths. First because they are only a "secondary" ground relying as they do with contact to the shield foil and also because heating up a pot can damage it (some have a tag on the side? Works better)

Take a solid, bare wire of about 22swg* from the jack sleeve tag and route that to the ground side of volume and tone pots. Make PUP grounds to that bare wire. Make a solid, purposeful connection to the cavity shield with a solder tag under a switch nut or even a dedicated 3mm nut, bolt and tag with star washer.

Keep all wires "scrunched up" to minimized open loops.

And check that amp's earth!

* ~ 21 AWG.

Dave.
 
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A lot of times the selector switch has some kind of frame ground lug. If the metal parts of your switch contact the shield foil, and that contacts the pot bodies, then that lug is a pretty convenient place to connect the shield to the jack sleeve.
 
Yeah, just to be clear I'm not necessarily saying I do that or he should do that,
but it's often the way it's done out of the factory and quite likely to be the bit that's gone wrong.

The washer thing is a good idea.
 
Steenamaroo said:
The washer thing is a good idea.
Click to expand...
You have to be a little careful how you solder the wire on so that you can actually install the washer after. What it really needs is a ring terminal, but a washer can work and is usually just already right there.
 
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