Help troubleshooting volume dips.

[psjon]

I have a rack of stuff and during recent gigs I've had issues with volume dips. At the last gig I got a better vantage point to observe it happening (I am playing and mixing simultaneously). The volume starts going down, slipping little by little. I turn up the mains, but then the volume starts increasing to the point of feedback and I turn it down. After a while it stabilized and wasn't a problem (not before sweating bullets). This, quite frankly, sucks.

The setup:
Yamaha MC Series mixer
Behringer DEQ2496
Older version of this 4-channel Carvin power amp: http://www.carvinguitars.com/products/s ... t=DCM2004L
J10s

Of course, my immediate suspicion is the power amp. I ran the mains mono on channel 1 starting out. After the first episode I switched the mains between songs to channel 4 on the amp and it happened again once more before it finally stabilized.

One other thing I've noticed about the amp is that the power doesn't seem the same on every channel even though they're rated the same: 1 seems hotter than the rest, 2 and 4 are about the same and 3 less. I just thought of something: maybe there's a bridging button on (but I think it bridges channels 2 and 3)?

These symptoms certainly point to a possible amp problem, but do the symptoms possibly point to anything else? Could it be the DEQ or Yamaha board? Cables (I have decent cordage)? Could it be a power supply issue (but I've had this happen at multiple venues)?

I am inclined to kick the whole rack to the curb and buy some kind of decent all-in-one powered mixer to make troubleshooting a little simpler. You know, now that I think of it, mixing your own sound is kind of a crazy proposition.

Any thoughts on this much appreciated.

[Bruce Weldy]

If you have an older model of the amp, it is probably less power. My guess would be that you are getting into thermal protection or engaging a limiter. The amp you linked is only 300 watts at 8 ohms....yours may be less. Are you seeing a clip light come on before this happens?

[wallywally]

You can quickly eliminate the DEQ by turning it off next time and see if it solves the problem. They have a direct thru when powered off.

[Bruce Weldy]

You can quickly eliminate the DEQ by turning it off next time and see if it solves the problem. They have a direct thru when powered off.

Behringer gear typically eats signal....but, usually at a constant rate

Still might be worth a try in the process of elimination. But my bet is still on the amp.

[Bill Fitzmaurice]

The mixer and DEQ should have output LEDS, so you can see if the output signal varies.

[DJPhatman]

A.C. mains power droop?