QSC 3402 distortion problem?

[jacove]

Hi,

I've just purchased a brand new QSC plx 3402 power amp to go with my Aguilar db680. I use one channel in stereo mode, but when I use channel 1 the signal distorts. also, the clip light flashes. I haven't experienced any distortion when using channel 2, but somehow the signal seems a bit weaker. I've tried with different cabs and it's the same. Could it be my cable?, I use a speakon wired 1+ 1-, but then why doesn't it distort from channel 2? Please help..Jacob

 

[jacove]

Well, I forgot to mention that the speakon output on channel 1 is much more stiff and tight than the speakon output in channel 2.

 

[DEVILMAN]

Try a different speaker wire. Sounds like your speakon connection. Did you unscrew the end & check the wiring? It might also in fact be a 2+ 2-...


~S~

 

[jacove]

Yeah, i've checked it, the red goes 1+ and the blue 1- in both ends. I use a Ampeg 610 and SWR triad if that is any help.

 

[DEVILMAN]

Do you have the user manual? If so, go to page 11 & 16. This might help you. Also, check your dip switch positions.


~S~

PS: Did you try switching the speaker wires or a different wire yet?

 

[jacove]

I've checked the manual, still haven't got a clue what the problem is...

 

[bill h]

What happens if you set it in parallel mode, then try the two channels?

 

[jacove]

in parallel the signal from channel 1 is also distorted...

 

[bill h]

in parallel the signal from channel 1 is also distorted...

Sounds like it need to see a technician. You may want to give "bob lee (qsc)" a PM to help. He is a member of this BB

How old is it? Did you just get it or did it just start to do this?

 

[jacove]

Thanks for your replys Devilman & Bill h

I bought the amp new a few days ago, I started playing in channel 2, no problem, then changed to channel 1 and first it sounded great, actually it seemed louder than channel 2, but then after a few minutes it started to distort.

 

[bill h]

Thanks for your replys Devilman & Bill h

I bought the amp new a few days ago, I started playing in channel 2, no problem, then changed to channel 1 and first it sounded great, actually it seemed louder than channel 2, but then after a few minutes it started to distort.

You should definitely give Bob lee a PM. Or call up the place you got it at.

 

[Bob Lee (QSC)]

Are you able to turn the cable's Speakon connector all the way clockwise in the amp's upper Speakon output?

Try putting a very light coating of silicone spray on the Speakon plug before you insert it into the amp. That may help it turn more easily.

 

[jacove]

I've plugged the speakon in/out for some time and it seems to be turning more easy now, I'll try with the spray if it doesn't get better...by the way Bob, have you got any idea about what is causing the distortion problem in channel 1.

 

[Bob Lee (QSC)]

If you don't turn the Speakon plug fully clockwise, you might get distortion due to a bad connection. That's what I would check out first.

 

[jacove]

The speakon can be turned fully clockwise and clicks in place. I've tried with different cables, and still the same distortion. The clip light flashes even on very very low gain. !

 

[Bob Lee (QSC)]

If you disconnect the speaker cable from channel 1's output, does it still clip like that? (Of course, you won't hear anything.)

Do you have the configuration DIP switches all set properly?

 

[jacove]

when I take out the output cable from channel 1 the red clip flash stops, my setting is for both channels stereo, limiter on and cut at 30hz.

 

[Bob Lee (QSC)]

You have switches 4–6 set to "stereo" and #7 set to bridge mono off?

And the same cable and speaker combination works on channel 2 without any problems?

 

[jacove]

Yes, channel 2 works with the same cables and cabs. 1-3 is set to the right, 4-7 to the left and 8-10 the right.

 

[Bob Lee (QSC)]

One more thing: I remember another customer having a similar problem a while ago, and the culprit turned out to be the way the Speakon connector on his speaker cable was wired. It was a two-conductor cable, but the Speakon plug was wired with 1+ / 1- in parallel with 2+ / 2-. As a result, everything worked okay when he plugged into the lower Speakon output but was distorted when he plugged into the upper one.

If the cable checks okay and you have switches 4–6 set to "stereo" and #7 set to bridge mono off (sorry, I don't remember off the top of my head which way is right and which way is left, but if you'll look, it's printed right on the amp), and it works okay on channel 2 but not on channel 1, then there's probably something wrong with the amp. Contact the dealer you bought the amp from, or contact EM Nordic A/S in Copenhagen, at +45 32 55 48 12.