GCX + Mark IV = Noise

[glenecho]

I am hooking my GCX up to a Mark IV. As an example of the problem, I can take the guitar, plug it into a Bad Monkey, and into the amp and I don't have any noise.

However if I create just one loop (Loop 1) on the GCX with the Bad Monkey in it...using the same cables it is noisy (verging on "hummy"). I still can get sound out of it and theoretically the loop works correctly turned on or off, but it's noisy. Even when the loop is deactivated there is an unacceptable amount of extra hum. I'm using high quality Lava instrument cables which all test out perfect if plugged straight into the guitar to the amp.

Any idea why the GCX is adding the extra noise? I thought it was supposed to make things, if anything, quieter.

[glenecho]

UPDATE: I tried plugging the guitar cable directly into the input on loop 1 and the hiss is gone. However now there is major buzzing going on when I turn up the guitar volume that was not there before.

[JohnClark]

UPDATE: I tried plugging the guitar cable directly into the input on loop 1 and the hiss is gone. However now there is major buzzing going on when I turn up the guitar volume that was not there before.

Is there anything else connected to the GCX, or the amp, when doing this test? The GCX loops are completely passive and unless there is something else connected somewhere, this loop is isolated from ground. What sits directly above the GCX? If you move any wall wart power supplies away from the GCX, does the buzz change in any way?

[glenecho]

Well I decided to go back to square one based on your feedback and simply take the GCX out of the rack and see what happens. When I plug directly into loop 1, I still have the crazy ground hum when I turn up the volume on the guitar, which was discouraging. However, I decided to go back to plugging the guitar into the Guitar IN and use the Feed Thru on the back into loop 1, which originally was causing me extra hiss. The hiss is gone.

So now I'm really confused...I'm going to try to re-rack it and see if the hiss returns. If it does I'll try moving it somewhere else in the rack. A Furman power conditioner was on top of it and a Fractal Axe FX was below it so perhaps there is a culprit there, though the noise was definitely hissy (like a line level/instrument level mismatch) and not electronic hum sounding.

As far as getting hum when plugging directly into loop 1 from the guitar, there is nothing else connected to the GCX...I'm simply testing out the bypass to make sure I'm not losing signal or getting hum (which I am). Nothing else is connected to the amp other than the Loop 1 out using an instrument cable.

EDIT: The culprit was the proximity of the GCX to the AxeFX and the Furman. When I shut off the AxeFX most of the hiss dissapeared and when I unplugged the Furman what remaining hiss there was disappeared. I moved the GCX to be below both the AxeFX and the Furman and things are much better now. Still a *slight* amount of hiss but it's only noticeable when the Mark IV is cranked with a ton of gain. I consider this part of the problem solved. I still don't know why I get such bad hum connecting directly to the GCX loop.

[JohnClark]

A loud hum when connecting guitar directly to a GCX loop and the out of that loop directly to the amp is very strange. There is no reason the GCX could make this happen normally. Is this GCX new or is it used and possibly modified in some way? Do you get the same result regardless of the loop used?

[glenecho]

A loud hum when connecting guitar directly to a GCX loop and the out of that loop directly to the amp is very strange. There is no reason the GCX could make this happen normally. Is this GCX new or is it used and possibly modified in some way? Do you get the same result regardless of the loop used?

Just tested and I do get the same result no matter which loop I use. I can connect my guitar cable directly to loop 5's in and plug loop 5's out directly into the front of the Boogie and it is noisy (buzzy might be a better word). Keep in mind...it's not noisy until I turn the guitar's volume knob up, as if it's causing the guitar itself to become ungrounded or something. When I use the normal front guitar in and use the Feed Thru into Loop 1 with a path cable I get none of that ungrounded sound in the guitar.

However, when I use the guitar in it seems more susceptible to picking up noise from the AxeFX sitting above it.

I purchased the unit new about 1 1/2 years ago and it has not been modded in any way.

Do you think my unit is defective?

[JohnClark]

As strange as it may sound, because this happens with any loop I believe that there is actually nothing wrong with the GCX. It is astronomically unlikely that every loop has suffered the same failure. I think the problem is most likely environmental noise coupling to the system or perhaps a faulty connection. Also, when running through the one GCX loop, you are running through both cables at the same time. The problem could stem from the overall distance of both of these cables.
Try testing with nothing powered up but the amp. The GCX does not even need to be powered in order to run signal through the In and Out of a loop. Have you tried cleaning any of the jacks? Do you have any other way to connect these two cables together, any true bypass pedal will work, in order to determine if the overall length is causing problems somehow? Do you have a second set of cables to try this test with just to eliminate any possibility of a faulty cable causing this?