Ground Lift / Hum Problems...

Question…

What causes 60-cycle hum sometimes when I try to hook up an on-stage guitar amp? How do you solve the problem?

Response...

The Red-Eye is normally used to connect an isolated acoustic instrument to a venue’s mix board so there is no connection to any on-stage AC power ground. In that situation, stage ground is not connected to the Red-Eye, so there should be no problem.

Connecting a pedal board to the Red-Eye's Effects Loop is not normally a problem either because pedal power supplies are normally isolated and there is no connection to stage AC power ground.

You only run into problems with AC ground loops and 60-cycle hum when you connect two AC- powered devices that are grounded to different AC power circuits through a Red-Eye at the same time.

An example would be connecting a Red-Eye to a venue's mix board ground via the XLR connection and also to an on-stage guitar amp ground via a 1⁄4-inch cable from the Red-Eye’sEffects Out jack. The AC power ground may be different for each AC circuit. Tying the soundsystem’s ground (via the Red-Eye XLR) and the guitar amp ground together (via the Red-Eye Effects Out) can induce 60-cycle hum in the single-ended connection, i.e. the guitar amp.

If you need to connect to an on-stage amp or some other AC-grounded device via the Red-Eye's Effects Out 1/4-inch connector and at the same time connect to a venue's mix board you will likely encounter 60-cycle hum. Some guitar amps have a ground-lift switch which solves the problem. If there is no ground lift on the guitar amp, you can try switching the “Gnd/Lift” switchon the Red-Eye or Twin to “Lift”. Depending on how the stage AC power is wired (or miss-wired) “Lift” may help. Ground lift is not a sure-fire cure. Sometimes using “Lift” just passesthe hum problem to one of your band-mates.

If you have an older Red-Eye or Twin without a Gnd/Lift switch you can use a ground-lift adapter to connect between the Red-Eye's XLR output and the cable to the mix board.

Here's a link to a popular XLR ground-lift adapter...

http://www.harkenspecialties.com/hk113.html

Others, as inexpensive as $10, are available through Amazon.