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[Art Welter]

Jake,

Some amps are noisy, and efficient HF devices will reveal that noise.

Some amps have very high amounts of voltage gain, and need to have the input gain reduced by switch or gain knob adjustment to allow the upstream equipment to be operated in their normal range.

What level on the console and EQ are required to clip the amp?

Have you done a hard wire bypass, plugging the XLR connectors together, to determine how much the EQ is adding to the noise?

[Don Boomer]

It's easier to hear digital noise than analog noise given the same level so gain structure is even more important here.  You haven't said anything about how you have it hooked up but typically most users have the sensitivity of their power amps up (too sensitive).

Try backing down the sensitivity knobs on your power amp say -10 dB and turning up your drive from your mixer by 10 dB.  That will lower the hiss by 10 dB.

Digital gear likes to be driven hard too.  For every 6 dB less that full scale you run them you lose 1 bit of resolution.

[Marty McCann]

The thing to watch out for in the cheapest EQ's (Not saying that yours is one of those), is those that use Gyrator (Sp?) circuits.  These are not true variable state filters, but cheap synthesis of same.  As a hint, any EQ where say you perform a cut at 100Hz, and you actually hear the hiss or the white noise floor increase, that is indicative of a Gyrator.

There should be a law against them.

marty

[jake hedlund]

Art Welter wrote on Tue, 16 June 2009 11:39

Jake, Some amps are noisy, and efficient HF devices will reveal that noise. Some amps have very high amounts of voltage gain, and need to have the input gain reduced by switch or gain knob adjustment to allow the upstream equipment to be operated in their normal range. What level on the console and EQ are required to clip the amp? Have you done a hard wire bypass, plugging the XLR connectors together, to determine how much the EQ is adding to the noise?

I have done a hard wire bypass and the noise is coming 100% from the EQ. Also, when the EQ is turned off (but the inputs/outputs are still plugged in) the noise disappears. Is it just a faulty unit?

[Art Welter]

If you have verified no EQ level or HF boosts are on, and turning the unit off or hardwire bypassing eliminates the noise, sounds like a defective unit, since several posters have said the Quad EQ is quiet.

One other (unlikely) possibility would be some other digital gear or computer radiated noise affecting it, did you try unplugging the AC on any other rack gear near the Quad EQ?

[jake hedlund]

Art Welter wrote on Tue, 16 June 2009 15:34

If you have verified no EQ level or HF boosts are on, and turning the unit off or hardwire bypassing eliminates the noise, sounds like a defective unit, since several posters have said the Quad EQ is quiet. One other (unlikely) possibility would be some other digital gear or computer radiated noise affecting it, did you try unplugging the AC on any other rack gear near the Quad EQ?

No I haven't. The amps are right next to the EQs (we have 2) and are on either side of one of them. I guess that could be a problem, but both EQs have the same problem. I guess they both could be defective...

[Art Welter]

Probably worth the effort to move them around, especially if the amps have switching power supplies.

I'm not really expecting this to be a cure, usually PSU induced noise is more "gritty" or "hummy" than "hissy", but you never know till you try.

[Kevin Callery]

Just an update, I ran the eq's 4 seperate channels on 4 monitor mixes 2 feeding Dynacord AM 12 powered monitors and 2 feeding Dynacord M12 monitors powered by a Dynacord S1200 power amp. The feeds to the power amp were slightly quieter but not much. The master wis set at -20db on all channels on the graphic and most of the aux were set about 12 o clock with the master aux set roughly the same. the hiss was livable and there were no complaints from the artists so I ran with it.

[Art Welter]

Kevin,

If you want to improve signal to noise, run the output of your console in the O VU range, the EQs at unity, as close to clipping as you can with some headroom, then bring your amps up.

You probably have your amp gain 10 dB higher than it needs to be, which raises your noise floor by 10 dB, sounding twice as loud.