QSC 1400 Issues

[Five String]

I have a Peavey Bassist preamp hooked up to a QSC 1400 power amp into a Peavey 1820 cabinet (biamp cabinet, 2 10's on top, 18 on the bottom) channel 1 into the high input, channel 2 into low.

The QSC 1400 is rated at 300W per channel at 4 ohms and the 1820 cabinet is rated at 4 ohms 300 watts Continuous and 600 watts Program on the high input and 4 ohms 350 watts Continuous and 700 watts Program on the low input, so I thought the two would be a good fit.

The QSC powers up fine, no clip light, and produces reasonable volume, but the sound out of the 2 10's is all midrange, even with the tone controls flat on the preamp. Adjusting the tone controls changes the sound very little, slightly lower midrange or slightly higher midrange.

The Bassist has an adjustable crossover, and when I turned it all the way up, to 2000 hz, that produced a pleasantly less midrangey sound, but still left me with little area for adjustment on the tone controls - varying degrees of midrange.

To make sure the preamp and cab were okay, I connected everything to my ancient, battered CS-800, and there were no issues whatsoever - full range of tone on the tone controls, crossover, etc.

The QSC is intended to relieve my back from the 68 lb. CS-800 should I so choose, but not if all I get is a very narrow range of midrange frequencies.

Any input as to how to get the full range potential from the QSC 1400, or whether there is something wrong with the amp, would be much appreciated.

[Alex1984]

I think that's the nature of how biamp rigs work, the 10s were supposed to be all midrange while the 18 covers the bottom. What does the back of the cab look like?

I guess another possibility is that your channel 2 is bust, have you tried swapping it around?

[gnjpowell]

Sounds like a crossover or bi-amp setup issue. Unlikely an issue with the QSC power amp.
Be sure you have:
Crossover low-pass > QSC Ch1 > the 18
Crossover high-pass > QSC Ch2 > the 10s
Depending on how you have the crossover setup you might get only mids & highs into the 10s. Be sure the inputs and the wiring to the drivers in that cab has not been hacked and works the way you are assuming it works...

[Five String]

Thanks, guys. There does not appear to be any issue with the biamp cab or the preamp. When I replace the QSC 1400 with my CS-800, I get a full range of frequencies out the 2 10's, from low to high.

I will certainly try switching the channels.

Thinking about it a little more, with the crossover set lower, I get lower frequencies out the 2 120's, but with the crossover set all the way up to 2000, I am able to produce the higher frequencies almost as well as with my CS-800.