ground loop humm...how the hell............

[maskedman72]

i have a loud ass hum coming out of my guitar cab.

the strange thing is the hum only comes on when i plug a mic cable from the output of my mic pre than into my a/d converter.

the stranger thing is all of my mic pres and the convertor are turned off!

i loosened up the mic pres from the rack and made it so they do not touch and the hum goes away,but these pres have to remain in my rack side by side.

the pres are 2 chandler ltd-1's and on the power supply's of each there are 2 grounding posts where i can connect a wire but i dont know where to connect the other end of the wire once it is connected to the power supply. i tried touching it to various things but it didnt make the humm go away.

also i am running a a/b-y splitter box to 2 different heads and if i remove this box,the humm goes away but i cannot do that durning tracking.

i tried plugging the gtr rig into another outlet but it did nothing.


how do i fix this problem?

thanks -jay

[aevan]

Not sure about the ground wire , but for y-cording to different amp heads simultaneously Smart research makes a distribution system that may help.
I think the site is www.smartresearch.co.uk

[sysexguy]

You have ground loop(s) and every loop creates more combinations of noise.

The first course of action is to get your two amps performing together which will require an a/b box that will isolate the two amps with an absolute minimum of signal damage. Lehle makes a box called a dual that has a transformer that only kicks on one side in when a+b is selected.

Another option is the Littlelabs STD which has a splitter with a ground lift.

You could also try using a wireless for the second amp ie. a/b box out 1 to amp 1, out 2 to wireless transmitter, receiver on amp 2.....while this may not be the ideal recording sound, it may help you eliminate the 2 amps from the problem while you check the pre-amp.

Once the amps are not humming along it's time to assure that you pre-amp isn't creating a ground loop with the sound card a/d.....first step may be to assure that all cables are the same length from pre's to a/d. The a/d and pre's psu should be on the same circuit. You may need to isolate the pre amps using shoulder washers and/or strips of tape to assure that the units aren't touching each other or the rack.

Andy

[maskedman72]

the a/b-y box i am using is an active unit by whirlwind.

i think i will put tape on the units in the rack that are touching.

i have never had a problem like this before but than again i have never used an a/b-y box either.

ther pres and the ad are on the same circut and the cables are of the same length.

thanks!

[h2000]

Glad to hear you have a solution. But, anytime you try to run multiple amps you run the risk of ground loops. I highly suggest the Voodoolab AmpSelector which was designed for just this problem:
http://www.voodoolab.com/ampselector.html
It has isolation transformers and silent switching and is very transparent. Check it out.

[Jeff A. Roberts]

Another option would be one of the many splitter devices from Radial Engineering.

As I recall, they use Jensen transformers. The top of the line JD7 which I grabbed has everything but the kitchen sink. Seven outputs, plus a balanced output, and variable loading to the source guitar pickups. They also make smaller stomp box sized units.

[max cooper]

This article was helpful to me; just thought I'd toss it out there in case it helps someone else.

http://www.soundonsound.com/sos/nov0...lation1102.asp