Popping noise when turning loop on and off - even with nothing in the loop

Q & A for building and interfacing your rack gear with Ground Control Pro and GCX-based systems.
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BobNad
Posts: 3
Joined: Sun Jun 02, 2019 7:06 pm

Popping noise when turning loop on and off - even with nothing in the loop

Post by BobNad » Sun Jun 02, 2019 7:52 pm

Hi,

I recently bought a GCX audio switcher with a Ground control pro. The GCX is an older model like 1994 or something like that. I'm trying to figure out if what is happening is normal or if the CGX or GCP are broken.

I get a poping sound when turning a loop on and off. I wanted to have a mute switch, so I had a loop with nothing in send-return jacks to cut the signal. 95% of the time I get a popping sound when turning the loop on and off.

My guitar is plugged in the front panel jack, feed thru in no1. Then out in one of the loops (tried all of them). I tried different pedals in the send return of the loops, same thing, whatever is in the loop (even a good cable between the send and return) doesn't change the popping sound. Tried to plug the output of the loop in my amp, still had the pop. Then plugged the output of the loop in my computer's audio interface, still poppin. Plugged the output of the loop in my Boss BR-600 (portable audio recorder) same result.

Tried to plug my guitar directly in the input of the loop (bypassing the front panel jacks). I also tried to plug the guitar directly in the input of the loop, then output of the loop in the feed thru in of the front panel (to have the buffer after the loop, read on this forum it could help) but still the same popping sound. I cleaned all the jack... nothing. All good cables, tried with older ones and new ones.


I don't know what to do, the guy who sold it to me said he had no popping sound, but he did not use it for a year before selling it to me. He is willing to pay me back. But I still want a GCX with a GCP I'll buy a new one... will I have the same issue? I have read here a lot of people have popping sound problems but most of the time they can isolate a bad equipement that when removed solve the problem. My GCX and GCP pop even with nothing in the loop. For me, a well working unit should not be popping at all, right?

Any help-advice will be greatly appreciated! Thanks

JohnClark
Posts: 7352
Joined: Tue May 05, 2009 2:33 pm
Location: The Lab

Re: Popping noise when turning loop on and off - even with nothing in the loop

Post by JohnClark » Mon Jun 03, 2019 12:21 pm

You certainly do have an older GCX, but that shouldn't mean that it just pops. On this one the main difference is that you have two buffered inputs on the front rather than just one. There hasn't been a lot of change inside a GCX over the years. The Loops themselves are 100% True Bypass so there is no circuitry in the signal path of a loop that can cause this sort of problem.

1. You may want to check that the GCX hasn't been modified internally.
Sometimes these older GCXs have been thru quite a lot in their time since leaving the factory. ;)
Common things to look for would be:
A. That the Chassis Ground Connection is in place. This is just behind the two front panel Feedthru jacks. It is a wire with a Ground Lug attached to a screw thru the PRE/PWR PCB.
B. That the loops haven't been "normaled" together in series. This one can be harder to spot since the mod is done under the Relay PCBs, but you can simply run signal to the In of a Loop then take the Out of the NEXT loop to your amp to check if signal passes when it shouldn't.
(Alternatively, if you want to just pop the top cover off this GCX and take a picture of the inside you can email it to us at info@voodoolab.com and we can go from there.)

2. Often popping is relieved with a buffer placed after the last loop. I see you tried this, but from your matching PM I see you have a Boss Tuner... try running the tuner right before the input of the amp so we can use it's buffer as a test.
3. For your "mute" it would probably be best to use the In and Send jacks. Signal to the In of the Loop and Send to the Instrument Input of the amp. The Send will always short its Tip to the Sleeve when the Loop is Off, this should completely Mute any signal from getting to the amp.

Let us know what you can!
------------------====Cheers!====------------------
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---------==Voodoo Lab Magician & Tech==---------

BobNad
Posts: 3
Joined: Sun Jun 02, 2019 7:06 pm

Re: Popping noise when turning loop on and off - even with nothing in the loop

Post by BobNad » Mon Jun 03, 2019 6:12 pm

Hi!, thanks for the reply really appreciate it!

I used the Boss TU-2 as a buffer with no luck (bypass and output jacks). I also was able to setup my nova system to turn the loop on and off without using the ground control, not better. But now I know it's not related to the ground control.

I tried playing the guitar while turning the loop on and off. The pop almost disapear while playing, it gets louder when the guitar sound start to fade. Its the loudest when no sound is coming from the guitar. I also swapped guitar, changed the Haggstrom for a SG, no luck with this either.

I opened the GCX, it looks clean, no excessive dust or corrosion. The ground looks wired like you described. For the normaled loops, didn't tried them all but went in the input of loop one and output of loop 2 the sound didn't leak. Tried them in pairs from 1-2 to 7-8. Tried linking all the loops, 1 to 8 and looks like they all work (but still pops).

I'll send pictures to info@voodoolab.com

Hope this will help you!

BobNad
Posts: 3
Joined: Sun Jun 02, 2019 7:06 pm

Re: Popping noise when turning loop on and off - even with nothing in the loop

Post by BobNad » Tue Jun 04, 2019 4:56 am

Hi,

Ran another test this morning,

Guitar in the boss tuner, boss tuner output in the input of first loop, decimator noise gate in the send return of the loop (also tried with nothing in the loop), then the output of the loop in the feed tru in of the front panel and then the feed tru output in the input of the amp. So one buffer after the guitar and one buffer before the amp. Still popping. Changed house to see if it was my electricity, same result.

I will let you know if I do other trouble shooting tests.

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