gcx and grounding

[TomMartin]

ok so i'm trying to wire up a rig that involves switching between the pre amp of my mark IV and a triaxis into the power section of my mark IV. In order to do this I will have to do this

 

loop 1 in --> guitar

loop 1 send --> mark IV in

loop 1 return --> mark IV fx send

loop 1 out --> loop 2 in

 

loop 2 in --> loop 1 out

loop 2 send --> triaxis in

loop 2 return --> triaxis out

loop 2 out --> mark IV fx return

 

 

now if i have loop 1 on i get my mark IV, loop 2 on i get triaxis into my mark IV's power amp. Well, needless to say I got some serious ground hum out of this, so I thought ok, lets make it simple and see where this is coming from. I tried this instead

 

loop 1 in --> guitar

loop 1 send --> mark IV in

loop 1 return --> mark IV fx send

loop 1 out --> mark IV fx return

 

so now with loop 1 deactivated I have my guitar routed straight to the power amp and with it turned on I get my full amp. Well this yielded exactly the same results as before. Even with the loop turned off.

 

Any ideas why this might be happening? I remember reading once that the GCX is often responsible for these grounding issues, but there is no actual AC ground on the unit! This is how it came brand new out of the box. I know the solution would be something like the ebtech stuff, but I would love someone to explain to me why this is happening with such a relatively simple setup, involving only 1 amp and a switch!

[Zachman]

 

ok so i'm trying to wire up a rig that involves switching between the pre amp of my mark IV and a triaxis into the power section of my mark IV. In order to do this I will have to do this loop 1 in --> guitar loop 1 send --> mark IV in loop 1 return --> mark IV fx send loop 1 out --> loop 2 in loop 2 in --> loop 1 out loop 2 send --> triaxis in loop 2 return --> triaxis out loop 2 out --> mark IV fx return now if i have loop 1 on i get my mark IV, loop 2 on i get triaxis into my mark IV's power amp. Well, needless to say I got some serious ground hum out of this, so I thought ok, lets make it simple and see where this is coming from. I tried this instead loop 1 in --> guitar loop 1 send --> mark IV in loop 1 return --> mark IV fx send loop 1 out --> mark IV fx return so now with loop 1 deactivated I have my guitar routed straight to the power amp and with it turned on I get my full amp. Well this yielded exactly the same results as before. Even with the loop turned off. Any ideas why this might be happening? I remember reading once that the GCX is often responsible for these grounding issues, but there is no actual AC ground on the unit! This is how it came brand new out of the box. I know the solution would be something like the ebtech stuff, but I would love someone to explain to me why this is happening with such a relatively simple setup, involving only 1 amp and a switch!

 

 

Lift the ground on the triaxis

[El Grinder]

 

Lift the ground on the triaxis

 

 

From his explaination, it seems he already tried taking the Triaxis OUT completely.

 

If not, then yes, lifting the ground on the Triaxis is definitely a place to start...

 

 

loop 1 in --> guitar loop 1 send --> mark IV in loop 1 return --> mark IV fx send loop 1 out --> mark IV fx return

 

 

 

Well this yielded exactly the same results as before.

 

 

Meaning ground hum?

 

I would like to say that using a high quality switching unit and high quality cables would eliminate such problems, but you are actually creating an electronic loop (from GCX to MKIV) that acts as an antenna to pick up noise (i.e. a ground loop).

 

Test each piece of gear individually, then build up. Stop and evaluate the situation where the problems start occurring...

[TomMartin]

 

From his explaination, it seems he already tried taking the Triaxis OUT completely. If not, then yes, lifting the ground on the Triaxis is definitely a place to start... Meaning ground hum? I would like to say that using a high quality switching unit and high quality cables would eliminate such problems, but you are actually creating an electronic loop (from GCX to MKIV) that acts as an antenna to pick up noise (i.e. a ground loop). Test each piece of gear individually, then build up. Stop and evaluate the situation where the problems start occurring...

 

 

Exactly, I broke it down about as simply as I could, by just switching between the mark IV pre and well nothing.

 

Well, as far as testing individually goes, the mark IV on it's own sounds exactly the way I'd want my whole rig to eventually sound. As for testing the GCX on it's own? Well i've never noticed any problems when switching pedals in front of the amp, or switching fx in the amps loop, or both at the same time. So to recap:

 

I've tested -

 

Mark IV on it's own - no problem

GCX switching pedals in front of amp - no problem

GCX switching fx in loop of amp - no problem

Triaxis into Mark IV return - no problem

GCX switching Triaxis into mark IV return - no problem

GCX switching mark IV pre into mark IV return - ground hum

 

 

what more could I test? Any reccomendations?

 

 

I'm using planet waves patch cables, are these not good enough to do this?

 

I guess I could try this with the loops on the 2290 and see if it's any different.

[TomMartin]

Ok somewhat intereting...if I touch the chassis of the gcx, effectively grounding it through myself most of the noise disappears

[Boltino]

 

Ok somewhat intereting...if I touch the chassis of the gcx, effectively grounding it through myself most of the noise disappears

 

 

I'd try isolating the gcx chassis from the rack (via humfrees) or open the gcx up and remove the ground to the chassis (green screw). I had some noise issues with my setup and was instructed to do this by voodoo labs (you might want to give them a call). They were very helpful.

[TomMartin]

Is using hum frees enough? What if it's a tightly packed rack and the chassis is in direct contact with something else in the rack not just through the rails?

[rackzilla2037]

I'm dealing with the same issue with a VHT pittbull and a Bogner 101b and a GCX. I am going to try the ground removal in the GCX to see if that makes a diff..

[Boltino]

 

Is using hum frees enough? What if it's a tightly packed rack and the chassis is in direct contact with something else in the rack not just through the rails?

 

 

Well, the point is that nothing is touching. If two components are touching you could stick an extra humfree (or any insulator) in between them. The easiest thing may be to lift the chassis ground in the GCX.

[TomMartin]

to rackzilla...this isnt going to be enough in your case im 100% certain of it. Eliminate the chassis ground on the GCX and you're still left with 2 amps each with their own ground. You may need to either lift the ground on one of your amps (SAFELY!) or isolate the ground on one of the amps using something like an ebtech hum eliminator, so a palmer line isolator.

 

So I finally got it to run silently with just the Mark IV in the loop. I went out and bought some George L's cable, and a couple of palmer pli-01's. I got away with just using 1 pli and my normal cables, the hum was gone

i then made up a couple george L cables, and didnt even need the pli. Whether it's the cables or maybe I moved something, I don't know. I did also disconnect the ground from the chassis of the GCX.

 

 

So.........I got a bit adventurous. I moved the Mark IV into loop 2, and put an overdrive pedal in loop 1. More noise again....not as bad, but enough to be annoying considering I want a silent rig. (no more noise than the amp with a guitar plugged straight in)

 

obviously, i know an overdrive pedal adds noise, but should it when it's turned off? And should it pick up radio stations? Uh oh....maybe I shouldnt have disconnected the ground on the GCX?

 

Well anyway, I moved the pedal back in the rack a little bit, and the noise went and so did the radio station. Back to sounding just like a guitar pllugged into an amp again.

 

Further inspection found that moving the pedal directly under the gcx picked up a load of noise...! So it is starting to look like the extreme close proximity of everything in my rack is going to be a massive issue.

 

I'm running

 

Case 1 : 8 space rack

Samson power brite - 1u

TC Electronic G Force - 1u

TC Electronic 2290 - 2u

Mesa Boogie Triaxis - 1u

GCX - 1u

2 spaces for pedals.....vary much not enough room.

 

Case 2

foam padded housing for my mark IV

 

case 1 is on top of case 2.

 

 

Am I going to be plagued with this type of stuff unless I get a bigger rack? What would you reccomend? Is it ok having everything touching as long as I let my pedals breathe a bit more?

[Spacehog26]

I have the same problem of an 8 space rack case with 8U of gear to go in it. Might be worth experimenting with the order of things in your rack, move the GCX up a slot or two, to see if that helps with the noise from the pedal. Certainly I've had similar problems with my RG16, and had to move things around to get the best sound. Not that I'm there yet, but it's getting better Keep persevering!

[TomMartin]

ok so todays experiments and findings

 

firstly i took everything out of the rack and put some electrical tape on the rails in the absense of any hum frees. no idea if this was worth it or not, but anyway...

 

i put my power conditioner and my gcx right at the top of the rack. in loop 1 one I had an sd-1, and in loop 2 I had the pre section of my mark IV, output of loop 2 to the fx return of my mark IV. I should also note, i dosconnected the ground from the chassis of the GCX. There was no green screw, but there was a screw through a black wire that went straight to the chassis, and was labelle GND. Is this right?

 

Well, business as usual. So I put a palmer pli-01 in between the gcx and the fx return on the mark IV, and the rig was quiet, and I was happy. Then my GCX started doing funny things, like turning all the loops on by itself. uh oh, did i disconnect something I shouldnt?

 

So I went back in and recconected the ground. Connected everything back up as before and now there was a horrible ground hum.

 

The only way I could get rid of it this time was to plug my guitar straight into loop 1's input. So in summary...

 

 

If you want to used the buffered input on the gcx without a horrible ground hum, you may have to disconnect the ground from the chassis inside the gcx...

[Boltino]

 

ok so todays experiments and findings firstly i took everything out of the rack and put some electrical tape on the rails in the absense of any hum frees. no idea if this was worth it or not, but anyway... i put my power conditioner and my gcx right at the top of the rack. in loop 1 one I had an sd-1, and in loop 2 I had the pre section of my mark IV, output of loop 2 to the fx return of my mark IV. I should also note, i dosconnected the ground from the chassis of the GCX. There was no green screw, but there was a screw through a black wire that went straight to the chassis, and was labelle GND. Is this right? Well, business as usual. So I put a palmer pli-01 in between the gcx and the fx return on the mark IV, and the rig was quiet, and I was happy. Then my GCX started doing funny things, like turning all the loops on by itself. uh oh, did i disconnect something I shouldnt? So I went back in and recconected the ground. Connected everything back up as before and now there was a horrible ground hum. The only way I could get rid of it this time was to plug my guitar straight into loop 1's input. So in summary... If you want to used the buffered input on the gcx without a horrible ground hum, you may have to disconnect the ground from the chassis inside the gcx...

 

 

I'm sorry you are having noise issues, but you can use the buffered input without noise. It just happens to be causing an issue with your particular setup. I would give voodoo labs a call. They will take the time to go over your whole setup and help you troubleshoot. They did this with my setup and helped me solve a problem that wasn't related to any of their equipment (the problem was a power supply for another unit). They are very helpful and will take the time to help you figure it out. Good Luck.

[TomMartin]

Of course, I've often used it without noise. But often with as well... in this particular case, to use it without noise I need to disconnect the ground from the chassis.

[TomMartin]

 

ok so todays experiments and findings If you want to used the buffered input on the gcx without a horrible ground hum, you may have to disconnect the ground from the chassis inside the gcx...

 

 

not saying you definitely have to in all cases, but if you're having issues, it's definitely a place to start.

[Boltino]

not saying you definitely have to in all cases, but if you're having issues, it's definitely a place to start.

 

[TomMartin]

Can anyone explain why disconnecting the ground on the gcx is causing it to turn loops randomly on and off?

[rackzilla2037]

 

to rackzilla...this isnt going to be enough in your case im 100% certain of it. Eliminate the chassis ground on the GCX and you're still left with 2 amps each with their own ground. You may need to either lift the ground on one of your amps (SAFELY!) or isolate the ground on one of the amps using something like an ebtech hum eliminator, so a palmer line isolator.

 

 

Good point. I guess I need to revisit that portion of this rig as well. THANKS!

[sacredgroove]

 

Can anyone explain why disconnecting the ground on the gcx is causing it to turn loops randomly on and off?

 

 

NO, that's weird!

 

I had to disconnect the ground from my GCX and I also upgraded the buffer opamp. Solved all of my GCX troubles.

[kiloIII]

fine. u win. : )

[kiloIII]

fyi, I was hoping to try and switch out for a 'brand name' model.

cuz this old one I had has past it's time.

 

not that I have anything wrong with GCX.

 

I've actually heard some great things.

came highly recommended by some friends of mine.

[sacredgroove]

fine. u win. : )

 

Unless I'm reading your post wrong, my post was supposed to be informative, possibly helpful--not a dig.

[Zachman]

After re-reading the entire thread, I can't help but wonder if the close proximity of your audio lines and your power lines isn't at least partially to blame for some of your issues.

 

Best of luck

[TomMartin]

Well I've made a lot of progress, it certainly isn't silent but it's a decent signal to noise ratio now. A few notes

 

My pedals add a lot of noise unless I use batteries instead of a power supply. No idea why, obviously batteries are the cleanest DC voltage source there is, so maybe my power supply just isn't very good.

 

Well, I gave my GCX and triaxis some room to breathe and put my pedals on top of the rack case. This solved my problem with the pedals picking up noise from other things.

 

My 2290 has decided to be really noisy and make intermittent crackly noises. Still haven't got any XLR's, but I hope the XLR ins and outs might be a lot quieter. If not, then it probably needs a good service anyway.