Loud hum through digital music corp audio switcher

[tobe]

Hello everybody,

I took a quick look through the threads, ie search, and did not find any info on this, but I apologize in advance if I missed it...there is alot of info on this site.

Here is my problem, years ago I picked up a DMC audio switcher and ground control, mainly so I could midi up my mesa. I have quite a few pedals and over the years I have become more anal about trying to reproduce recorded sounds on stage, so a while ago I tried to implement the audio switcher for its audio abilities, as well as midi..., and was rewarded with a loud hum. At around the same cycle rate as a ground loop problem. I talked with various tech people and tried isolating the switcher out of the rack through various methods, including physically removing it, using different cables, shielded, non-shielded, etc, and still got the same hum. All the time, non stop 24 hour party of HUM. Now, I believe that the switcher actually boosts the signal of the guitar, I think anyways, the brain, does not work the same as it used too , so my only other idea on the hum, other than it being a ground loop issue, was perhaps it was pushing the pre amp in my mesa too hard, because of the amplified signal from the switcher.....Any thoughts on this? I just got a steve's special purple VHT 2150 with an insane amount of output, and I thought about putting together more of a rack system again, and once more try to incorperate the switcher feature on the unit, perhaps through a mesa recording pre amp rectifier...but I wonder if the hum will still be there. Other than putting a hush unit in the rack, which I don't want to do...I really can not use the switcher unit without removing this hum thats driving me, and the techs nuts!!! arrggghhhh!! :P Any help would be greatly appreciated! Party on Tobe

[Akhenaten]

Did you buy it used or drop it? A friend of mine had the same deal with his and it started after it got knocked. I had it for awhile, and the same deal happened with my system, using a triaxis and a Mesa Stereo 500. The GCX is a cool system once you've got it happening, but it seems a bit touchy. But have it checked out internally if you have someone around that does that. Also, and this may sound funny, but check to make sure nothing is plugged in backwards. I'm sure since you've done a search and everything, you have probably done that. But once we hooked it up and had something reversed, and it hummed...lol

[tobe]

Thanks for the thoughts, I got it brand new from Digital Music Corp. Of course, it has seen many hours of being moved around and jostled, not everyone takes as good of care as my gear as me, and thats not saying much! So I guess that might be a possibilty, but if I remember right I tried it pretty early on, and did hum then too....but I guess it wouldn't hurt to have a tech pull it apart to check the conections. Thanks again, any other thoughts? Tobe

[Gearjunky]

The DMC GCX is a simple construction of jacks and relays. There is nothing that can really be hurt by dropping it.
I would take the cover off and see if there is any type of loose connection or cold solder. And check for any loose pieces of metal wire or solder floating around.

[tobe]

hmmm...okay do you think there is and validity to the possibilty that the switcher could be driving the pre amp to hard, resulting in the hum? thanks again

[vaijem777]

I'm pretty sure that it's not possible for the GCX to "drive" the preamp. I've had mine for about a year now, and have had no issues with it whatsoever. But, when I first got it, I spent some time on the phone with the guys at GCX, and they were great to deal with. Give them a call, and I'm sure they'll be more than happy to help you out

[tobe]

Vaijem, thanks for the thoughts, when I first got this unit and encountered this problem, I called them first, and thats where I got a lot of ideas about isolating the unit from the rest of the rack, etc, and it still did it...I mean this is not a little hum, its loud, way too loud fer sure. They were nice at first and gave me some good points of departure for fixing the problem, but as with alot of tech support when it is not the most obvious thing, like the old cliche is your computer turned on kinda thing, they kinda fell apart....very preplexing problem to say the least, but thanks for your input...how do you have the signal path set up? Do you run the audio from the swither into the input on your amp, or do you run it through your effects loop? Are you using rack gear or a head? Thanks again, Tobe

[vaijem777]

I run my GCX directly through the input of the amp-not through the FX loop. Here's my current setup:



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[tobe]

Thanks for the pics. Thats what seems so weird...that is the way in the past I have attmepted to set up my signal path. Through the switcher in to the loops, then into the input of my amp...but always that dag durn hum....Granted I am a little kooky, but you would think this wouldn't be so hard to set up.....I'm mean this is not rocket science...or is it? but at least I know that others use a similar set up without the hum.....

[Gearjunky]

Go directly from your guitar into the GCX, then out to your amp. The GCX is your fx loop.
The GCX is a line buffer, and should actually quiet down your signal path as if you were plugged directly into your amp itself.
There is no circuitry in the system either, so there is nothing in it to create noise. It is point to point wiring with true bypass.
Do this to see if the unit has a short that is creating the noise.
Just have 4 cables(one from your guitar, and one to the amp and 2 extras for a pedal)
1. Plug directly into the GCX input.
2. Take the cable from the rear out of the GCX marked feed thru 1 or 2 and go to your amps input.
At this point, it should be the exact same thing as plugging directly into your amp without the GCX.
It should be just as quiet as when the GCX is not in the line.
3. One by one check each loop by taking the output cable of the GCX to input of each loop (1 thru , while putting a patch cable from the send of the GCX to the input of your pedal, and a patch cable from the output of your pedal to the return of each loop (1 thru and then another cable from the out of each loop.
By doing this you should easily be able to see if it is a single one of the 8 loops creating the noise.
Just make sure that you individually test every single cable that you are using to ensure that it is not a bad cable, which is the most common reason for the noise that you are getting.
I also suggest that you get some George L's cables to wire up the whole system, that way you will have the highest sound quality, and no excess wire mess.
Hope this helps.
PM me if you want me to call you during the testing.

[tobe]

thanks gearjunky and vaijem....you both had good insights, I have tested like you suggested in the past, but I revisit this and see what happens this time around...I let you know what I find out..Tobe

[Gearjunky]

You'll probably kick yourself in the ass once you realize that you had a bad cable or had something hooked up backwards. LOL
It happens to the best of us.

[tobe]

Thanks again everyone for the thoughts, I have tried everything, short of picking up an 2nd unit to A/B with, I still get the hum. I tried different cables, etc, through my mesa, with/out effects, etc, through a pod pro into a VHT 2150.....still got the hum...With the 2nd set up, with the noise gate on most the hum was removed, but it was still there....It is definitely something to do with the switcher, cuz when I do not have in the chain...no buzz is present...

[Gearjunky]

Did you open up the unit to see if there is a loose connection or metal fragments from wire or solder in there?

[tobe]

Just a quick update....Thanks for all the advice, but still no luck, so its being shipped back to Digital Music Corp. I just do not have the time to deal with it anymore... They were stumped over the phone as well, so we'll see what we see...Tobe