Power Question

[ned911]

So we played a gig at a hotel last night - outside. Told that each power drop was a seperate circuit so we put the power amps on 1, mixer rack on another and everything else (lights, POD's) on the 3rd.

 

The power amps were creating a horrible hum. Re-routed the power through the Furman and the hum disappeared.

 

What was causing the hum - ground loop?

[Gregidon]

I'd be willing to bet it was either ground potential between the outlets or a miswired outlet. A outlet tester (

 

Did you plug the mixer rack into the furman as well?

[Ear Abuser]

I'd say yes it was a ground loop- If you can't keep the mixer and power amps on the same circuit, you may need to lift the ground on the feed from the mixer to the power amps. Sometimes you need to use an 1:1 isolation transformer in the feed and lift the ground.

Usually easier to just feed the mixer from the same circuit- A mixer and outboard goodies usually don't draw to much AC unless you have a pretty big set -up.

[agedhorse]

If moving to one circuit (Furman or not) eliminated the ground, it was most likely a difference in ground potential causing a ground loop. The Furman probably had nothing to do with correcting the problem.

[Craig Vecchione]

There's nothing you can do to fix a ground potential problem in the building wiring except let the PIC know, so there's no point in trying to measure it. When you run into this issue, do as you did if the common power source can handle the load, or isolate the components with 1:1 transformers.

[ned911]

Mixer rack always runs through the Furman. Since this was the first time we were running 4 SRX718S's from the ITech4K we wanted to have it on a seperate circuit since they were available.

 

Normally I run a PowerCon out from the mixer rack to the PowerCon in on the amp rack which is what we ended up doing last night.

 

Gig was outdoors BTW.

[Barryjam]

How was the Itech4000 with those 4 subs?

[ned911]

Very, very nice. I would really like an IT6000 for them but not in the budget.