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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB Lounge FUD Forum Archive => Topic started by: Kevin Callery on May 27, 2009, 11:05:29 AM

Title: Mackie Quad EQ with a lot of Hiss........
Post by: Kevin Callery on May 27, 2009, 11:05:29 AM

Hey all I recently acquired a Mackie Quad EQ for my monitors but I have found it has a lot of high end hiss on the output. Has anyone else encountered this problem? On a noisy stage it's not really a concern but on a quiet stage it's very hard to balance the signal to noise ratio. Any help would be appreciated.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Dick Rees on May 27, 2009, 03:30:27 PM

Kevin Callery wrote on Wed, 27 May 2009 10:05

Is the hiss present without anything connected to the unit? If so, then you've got yourself a noisy unit. If not, then the problem is most likely the system gain structure. If that's the case you are picking up noise where the gain is close to the noise floor and then brought back up to an unacceptable level further down the line.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Steve Hurt on May 27, 2009, 08:41:44 PM

I had Quad EQ for a while and they're pretty darn quiet. If the EQ is making the noise, then it has service issues. How do you have it patched in?

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Jay Barracato on May 28, 2009, 06:52:09 AM

Does the unit have a bypass?

I would be interested if the hiss is present when the unit is bypassed. I have a GEQ that just seems to have its own noise that is only noticeable when there is no other signal. The hiss goes away in bypass.

Jay

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Kevin Callery on May 28, 2009, 11:24:47 AM

I've routed it with the signal directly fed through the xlr's and also inserted it into the aux out and it seems to be the same either way. I can live with the signal to noise ratio on the monitors with a bit of a balancing act but there's no way I could use it on FOH. Just a bit of a pity cos it's such a neat unit....

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Tom Reid on May 28, 2009, 12:35:59 PM

Kevin Callery wrote on Thu, 28 May 2009 10:24

Yes a very neat piece of gear.
I use mine to do 4 way monitors from FOH.
No hiss.
I run aux 1-4 xlr in to xlr out to snake, to 2 crown xs1200.
Even with hi gain on the amps it is dead quiet.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Art Welter on May 28, 2009, 12:45:52 PM

Kevin,

Are you sure you are not boosting gain with the EQ, 10 dB is available.
Boosting above 5K would also increase hiss.
What happens when you hit bypass?
What happens when you use the same two XLR plugs that went through the unit and connect them together?

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Alan Roberts on May 28, 2009, 03:57:47 PM

I've noticed hiss only when the EQ is hooked up to powered speakers with digital amps.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Kevin Callery on May 28, 2009, 06:57:04 PM

I've a festival coming up this weekend and the rack is currently packed for moving so I'll have to have a good run through it before sound checks begin to see how I can get the most out of it.
I'll have 4 monitor mixes so I'll be running all 4 channels so I'll see how it behaves

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: jake hedlund on June 16, 2009, 02:05:43 PM

I am having an identical problem with the same equipment. Bypass does nothing and the hiss is there even if there are no inputs plugged in. I am using shielded XLR cables for everything. Any ideas of what could be wrong?

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Art Welter on June 16, 2009, 02:39:45 PM

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?

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Don Boomer on June 16, 2009, 03:03:30 PM

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.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Marty McCann on June 16, 2009, 04:33:59 PM

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

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: jake hedlund on June 16, 2009, 04:47:32 PM

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

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?

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Art Welter on June 16, 2009, 06:34:55 PM

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?

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: jake hedlund on June 16, 2009, 07:11:41 PM

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

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...

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Art Welter on June 16, 2009, 08:25:28 PM

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.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Kevin Callery on June 17, 2009, 10:53:28 AM

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.

Title: Re: Mackie Quad EQ with a lot of Hiss........
Post by: Art Welter on June 17, 2009, 01:07:19 PM

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.