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Old Sunday, May 7th, 2006, 03:54 PM
libbym78's Avatar
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soundcraft spirit live noise

We have a Soundcraft Spirit 4^2 mixer. 32 channel, 4 Subgroups,

We have had problems with buzzes, hums, etc. Part of the problem was wiring--which we have replaced the signal wiring from the mixer to the amps. That got rid of some sporadic buzzes, etc.
<O
However, to my disappointment, much of the noise seems to be coming from the Subgroups on the board (I had hope that rewiring would get rid of the noise)

<O
Typically, we route all of the channels through one of the 4 subgroups (vocal on one, guitars on another, etc). I found, yesterday, that the more channels routed to the subgroups, the more noisy the output of the board becomes. If I, instead, route all of the channels directly to the main outputs--bypassing the subgroups (by pressing the "mix" button instead of the 1-2 or 3-4 buttons on each channel) there is essentially no noise.
<O
The noise is incremental based on the number of channels routed to the subgroups. If there is one channel routed to the subgroups it is quieter than if there is two, which is quieter than if there is 5, which is quieter if there is 10 and so on.
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Is this something I should expect from this mixer, or is there something wrong that can potentially be fixed?
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Any thoughts or ideas would be helpful.
<O
Thanks

MIKE
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Old Sunday, May 7th, 2006, 05:32 PM
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Welcome to satan's torment for the sound crew

There are still TONS of things that could be causing that buzzing. Once we would get little bits of static in our board. Ended up (after paying to clean amps, check wiring etc) that an old effects processor had a dirty pot. Even when muted it would send static throughout our whole system...it was really weird.

The only way to truely find out is to run your board clean and slowly plug in each channel and test it to make sure that it's not a cable or another component somewhere else.....
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Old Sunday, May 7th, 2006, 06:51 PM
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Check your gain structure

what you want to make sure is that you are feeding a relatively hot signal at each point, so that you are not really cranking the pots for excessive gain at any given point. A goal is unity gain at each point-generally not really possible, but a good goal. Warning signs-clipping on any of the channels (not familiar with your specific board, but requently clip lights are available on every channel). If this is happening, then either turn down your gain/trim pads, or add a 20-30 db pad-ususally available near the gain knobs. Another issue can come if you have to have your faders way down on any channel or the group faders. You can overdrive the summing amps-you can correct for slightly hot levels but bringing the faders down a bit, but if you're down around the 10-20 % mark on the faders-you are feed the buss way to hot of a signal.
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Old Sunday, May 7th, 2006, 07:36 PM
MPCC Media's Avatar
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Our spirit live board had to be sent in for refurbishing, which is kind of costly.
But what you discribe could be dirty faders. Cleaning them is simple. Simply grab on the fader that causes the problem, and rapidly slide it up and down for about a minute or two for every fader. It has to be fast, not just push up and down. That will clean off any dust collecting on the fader's contact points to ensure a better signal flow.
Try it, see what happens. Build your arm muscles at the same time.
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Old Sunday, May 7th, 2006, 09:01 PM
Gzsrulz
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Quote:
Originally Posted by MPCC Media
Our spirit live board had to be sent in for refurbishing, which is kind of costly.
But what you discribe could be dirty faders. Cleaning them is simple. Simply grab on the fader that causes the problem, and rapidly slide it up and down for about a minute or two for every fader. It has to be fast, not just push up and down. That will clean off any dust collecting on the fader's contact points to ensure a better signal flow.
Try it, see what happens. Build your arm muscles at the same time.
a few simple steps to clean faders, dont bother with triclorothane/blackothane/674/etc anything plastic will melt and most paint will peel off , the contact cleaner from rad shack is not well made either, it has a stay behind lube that can cause issues too in the long run

to make it as simple as possible, buy a bottle of zippo lighter fluid, then unplug the console, put a bit of the lighter fluid in the fader, move fader up and down really fast for a few seconds, then move to the next fader, it also works for pots and contact switches VERY well

lighter fluid is by far the best cleaner i ever found, but make sure the console or device is unplugged as remote as it sounds, an arc can ignite it, and it leaves no residue behind, it wont work for silica based dirt as sand, but will help with dust and dirt

i saw a guy clean a console with WD40, i decided that company was not a very good place to work and add to my resume`

Blessings

Last edited by Gzsrulz; Sunday, May 7th, 2006 at 09:02 PM. Reason: Merged Double Posts
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Old Monday, May 8th, 2006, 09:00 AM
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It sounds like one of a couple of things. Either your ACNs (Acive Combining Networks also called summing amps) are going bad in your sub groups, or your gain structure is off. There are 2 basic ways of doing gain structure at aa console.

One is the mackie way. You PFL your channel so that the input amp is feeding your main meters and you turn your gain up while and instrument is playing and you try to get your meters to read about zero. This is fine for small ensembles or spoken word. But if you have many channles feeding your groups, then you can overload your groups.

The other way is to slide your iput faders to the unity or "0" mark on the console. First make sure your gains are all the way down. Then slide your groups and master to Unity or "0". As the instruments are playing, adgjust your gains so that the volume is acceptable without getting clips on the channels. This should produce a clean even signal through your groups and help out with some of the noise issues you are having. This also assumes that the gain structure to your processing and amps is set up correctly. If this does not help your noise, than it is probably the ACNs.
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Drew
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Old Monday, May 8th, 2006, 09:35 AM
Nathan J's Avatar
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Quote:
Originally Posted by libbym78
<o><o><o><o>Is this something I should expect from this mixer, or is there something wrong that can potentially be fixed?<o><o>
Others have covered the problem, but I just wanted to clarify again. I have this board and no, this is not something to be expected.


</o></o></o></o></o></o>
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Old Monday, May 8th, 2006, 06:32 PM
libbym78's Avatar
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Quote:
Originally Posted by Drew Ryan
It sounds like one of a couple of things. Either your ACNs (Acive Combining Networks also called summing amps) are going bad in your sub groups, or your gain structure is off. There are 2 basic ways of doing gain structure at aa console.
Im sure it isn't a gain structure problem because it happens even when all of the channels are muted. The only difference between noise and no noise is having channels assigned to the groups. I also am a stickler with maintaining good gain structure.

I am leaning towards something being wrong with that stage of the board.

I am also pretty sure that it isn't dirty pots, i haven't ever noticed any scratching, etc as I move the pots. This is a constant noise (whenever I am using the subgroups)

Thanks for the thoughts. Does anyone know what we would expect to pay for a repair (or replacement) of the subgroups? The board also has two channels that are dead (I believe that it was purchased used about 7 years ago (just before my time at the church) so we could stand to send it in.

Mike
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Old Monday, May 8th, 2006, 11:17 PM
MPCC Media's Avatar
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It's expensive, I believe our quote from Soundcraft was about $2000 or so, which is about as much as MPCCs yearly media budget, so ours is sitting and collecting dust right now.
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Old Tuesday, May 9th, 2006, 06:42 AM
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Quote:
Originally Posted by libbym78
Does anyone know what we would expect to pay for a repair (or replacement) of the subgroups? The board also has two channels that are dead (I believe that it was purchased used about 7 years ago (just before my time at the church) so we could stand to send it in.
I paid about £40 for a replacement main mix board on this model. So replacement channel boards should be available for a reasonable price.

Do you get the noise on both sets of subgroups? If so that would seem to eliminate a subgroup board problem. Is the ribbon bus cable seated on each board properly? Another place I would look is the PSU.
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