Do I have a ground loop problem?

Luca Brasi

Luca Brasi

New member
Hi,

I've asked this question on the Digitech GNX3 forum and got no answers so I thought someone here might be able to help.

I'm using two electric guitars for recording. Both run through my Digitech GNX3 into my M-Audio 2496 card. Both have Bumblee caps and CTS pots.

My first guitar records with no problems, no hums. My second guitar records but has a terrible hum when run through the GNX3. I can't take my hands off the strings or I'll get a really obnoxious hum/buzz. This is driving me nuts because this one is my primary guitar!

Here's the kicker though...I'm using the same cable for each guitar, and neither guitar has a hum when run through my amp (here again I'm using the same cable), not even a hint of a hum. I'm also using the same settings on the GNX3 for each guitar.

I'm wondering if I don't need one of those computer repair grounding wrist straps clipped to the bridge or something.

Anybody have any ideas?

Thanks in advance.
 
when you say you have no hum when the guitar is plugged into the amp,,

is that guitar>amp or guitar>gnx3>amp


if it's not the latter,,,try that out and see what you get.
 
Is the primary guitar a single coil guitar?
Digital boxes can emit all kinds if nasties that get picked up with close proximity.

I keep some small jumper wires with alligator clips...and in those instances, I will find two ground points within the setup that eliminate the problem.
There have been a couple of times in the studio where I've stood barefoot on the end of a jumper wire to kill the hum since all other attempts failed. :D

PS...caps in passive guitar electronics don't benefit from expensive brands/types. You will get the same results with the Radio Shack "green chiclets"...though I'm sure lots of guys will say they can hear a difference. :)
 
Steenamaroo said:
when you say you have no hum when the guitar is plugged into the amp, is that guitar>amp
Click to expand...

Yes, I don't use the GNX3, just direct into the amp. I'll try it the other way tonight.

Is the primary guitar a single coil guitar?
...caps in passive guitar electronics don't benefit from expensive brands/types. You will get the same results with the Radio Shack "green chiclets"...though I'm sure lots of guys will say they can hear a difference.
Click to expand...

The first guitar has two Seymour Duncan humbuckers with an EMG single coil in the middle, no hum on either of the three pickups. My primary guitar is just two SD humbuckers. All pickups are passive. As for the caps, I could immediately tell a difference after I installed the caps. The tone is "warmer." I only mentioned the caps because I was wondering if mabye I've got a bad cap.

Thanks.
 
It's not a ground loop but some other kind of EMF, like Miroslav said there are all sorts of things in play in a recording situation. I know when I am recording any single coil guitar or bass there are some things I have to turn off or a particular place to stand/sit to avoid electronic hum.
 
Luca Brasi said:
It was remarkable difference in tone, worth the extra money. Of course, considering the guts that were in the guitar perhaps it wasn't so remarkable...
Click to expand...


Were the new caps exactly the same values as the original caps?
Maybe that's the difference you are hearing?

I'm not doubting you...it's just that a long time ago I was also on the cap upgrade idea, as I kept seeing guys mention it.
But after I did some research as to which types/brands would be the best choice...I found a lot of info pointing out that in a passive circuit (like your guitar pickups)...the only thing that matters is the *value* of the caps...and that spending lots of $$$ on high-priced ones was a total waste.
For active circuits it's different.

And after thinking about it...it makes electronic sense. Many of the guys that were debunking the cap upgrades had solid electronics behind them...guys that build amps and whatnot.

Maybe a few of the more advanced electronics experts on the forum could chime in on this? I’m just going by what I’ve read from other sources.
 
Luca Brasi said:
I tired that, and I get the hum when I go guitar>GNX3>amp.
Click to expand...

Try the ground jumper wire approach I mentioned.

Connect a wire to the GNX3 somewhere on it's metal case...one of the screws...etc...then touch the other end to something else, like the amp chassis, or anything else that is plugged in, like another amp, etc (those need not be turned on)....
...and see if you can find a combination that kills the hum.
Worst case...stand barefoot on the end of the wire to kill the hum while you play (it's easier than trying to connect it to your wrist or whatever)...it works. :D

Yeah...it's all a temp solution, but for recording that's all you need.


Playing live, a little hum isn't going to be a big issue....
 
Miroslav,

Thanks for your suggestions. Yes, all the caps are the same values. There are two in my primary guitar (LP) and one in my Ibanez (only one each vol and tone pots). I've got some wires with alligator clips and I think I'll try to rig up some sort of grounding circuit with that and see if that helps.

Thanks all!
 
Luca Brasi said:
It was remarkable difference in tone, worth the extra money. Of course, considering the guts that were in the guitar perhaps it wasn't so remarkable...
Click to expand...
I am skeptical about the vintage capacitor thing, especially in passive circuits, and if you have the tone(s) on your guitar set wide open, the cap(s) are essentially out of the circuit, anyway. But hearing is subjective; if you hear a difference and it's worth the money and trouble to you to make the modification, then go ahead on.
 
I have been cables like this https://homerecording.com/bbs/showthread.php?t=294090 for a long time and it gives me the max protection against ground loops. Most all my cables are made that way. I haven't bought a "made" guitar cable in 30 years, in general the ones you buy suck and if they are any good they cost 3 or 4 times as much as the ones I make.
 
I express no opinion on the audible effects of caps in a guitar, but I can't think of a reason that there would be a difference between a passive and active circuit. That doesn't make "electronic sense". A circuit is a circuit. Capacitor distortion is dependent upon capacitor type, signal level, and circuit bias. An active circuit may be more likely to have a higher signal level, and it's a lot more likely to have DC bias ;), but that doesn't mean that capacitor distortion cannot be experienced in a passive circuit.
 
dintymoore said:
I have been cables like this https://homerecording.com/bbs/showthread.php?t=294090 for a long time and it gives me the max protection against ground loops. Most all my cables are made that way. I haven't bought a "made" guitar cable in 30 years, in general the ones you buy suck and if they are any good they cost 3 or 4 times as much as the ones I make.
Click to expand...
Wiring a cable like this does nothing for ground loops. It's still a two conductor unbalanced high Z connection, and with an unbalanced connection whether or not you have a ground loop depends on how/if the components are grounded, not the connection between them. With a balanced connection the shield is not part of the circuit, so you can connect the shield only at one end so that the chassis of the components are not connected, but this is not an option with an unbalanced connection.
 
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