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Author Topic: Noise/static elimination  (Read 4574 times)

Hal Bissinger/COMSYSTEC

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Re: Noise/static elimination
« Reply #10 on: October 24, 2015, 02:51:34 pm »

Not crazy to swap in a small mixer just to test and confirm no larger systemic issue.

I agree. This really sounds like a problem with the mixer. How old is it?

-Hal
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Stephen Swaffer

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Re: Noise/static elimination
« Reply #11 on: October 24, 2015, 03:57:26 pm »

Mixer is around 8-9 years old.

I haven't answered the fader question because I can't give an accurate answer. This afternoon,  I have to go put things back together after the disassembly I did during The Wednesday evening service. From thoughts on here, sounds like I will finish disconnecting everything and see what results I get. I will also experiment with master fader.

I have also located a 16 channel mixer that is available for our use that might give me a window of opportunity for repair.  We can get by with that if we have to.

The biggest conundrum I see is that IF external sources are acting as antenna and that noise is being rectified in the mixer, then either removing the antenna or repairing the mixer potentially eliminates the problem-and repair is the only action with usable results. 

Update: For once an intermittent problem cooperated.  With everything disconnected except a pair of headphones we still have static.  The static does respond to main fader and main mute-but it is still discernible with the headphones.

So topic swerve.  We also have 4 noisy channels we no longer use (48 channel mixer).  Repair or replace?
« Last Edit: October 24, 2015, 05:15:21 pm by Stephen Swaffer »
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Lee Buckalew

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Re: Noise/static elimination
« Reply #12 on: October 24, 2015, 06:50:35 pm »

Mixer is around 8-9 years old.

I haven't answered the fader question because I can't give an accurate answer. This afternoon,  I have to go put things back together after the disassembly I did during The Wednesday evening service. From thoughts on here, sounds like I will finish disconnecting everything and see what results I get. I will also experiment with master fader.

I have also located a 16 channel mixer that is available for our use that might give me a window of opportunity for repair.  We can get by with that if we have to.

The biggest conundrum I see is that IF external sources are acting as antenna and that noise is being rectified in the mixer, then either removing the antenna or repairing the mixer potentially eliminates the problem-and repair is the only action with usable results. 

Update: For once an intermittent problem cooperated.  With everything disconnected except a pair of headphones we still have static.  The static does respond to main fader and main mute-but it is still discernible with the headphones.

So topic swerve.  We also have 4 noisy channels we no longer use (48 channel mixer).  Repair or replace?

Well...that depends on other troubleshooting.
The noise is still present even with all input (don't forget the talkback mic if you have one) and output connections disconnected from the console AND with all input channels, aux returns, groups, etc. muted and faders at infinity?
There are no cables connected to the console except the headphone cord and the power supply cable, correct?
There are no insert connections from the console either correct?
No signal was routed to the master?
The pink noise generator is turned off and potted town and unassigned?
Have you excersised all of the buttons and knobs at some point when soloing each channel (EQ in/out, mic/line, HPF, polarity/phase switch, phantom power, etc.)?  Sometimes analogue controls can develop a portion of their travel that produces static. 

Does the power supply have a properly wired IEC power cord and is there a known good outlet/circuit feeding it?

Does the same noise appear and behave the same way with only left main fader up and only L-R selected in the Monitor section?
Does the same thing occur if you pull down the left main fader and push up the right main?
Again with mono but deselect L-R and select M in the monitor section, any difference?
If with all busses unassigned and nothing even being routed to the master (even all the little extra bits in the master section that could route external signal or the internal generator to it) you still have noise in headphones when soloing the output masters then I would say the board needs service.

As has been suggested by others a quick swap to a different console would tell you if the problem stayed or went away.

Lee
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Lee Buckalew
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Nicholas Quek

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Re: Noise/static elimination
« Reply #13 on: October 26, 2015, 01:40:26 am »

Had a problem exactly similar to yours before on an old mixer,  replacing the power supply filter caps fixed the problem... 

Noise came back after about another 8 years and then did the same thing to fix it again.


Sent from my iPhone using Tapatalk
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Stephen Swaffer

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Re: Noise/static elimination
« Reply #14 on: October 26, 2015, 04:44:02 pm »


There are no cables connected to the console except the headphone cord and the power supply cable, correct?

Does the power supply have a properly wired IEC power cord and is there a known good outlet/circuit feeding it?


 

Update: For once an intermittent problem cooperated.  With everything disconnected except a pair of headphones we still have static.


I guess I should be precise and state power was connected-but assumed that listening to a board with power disconnected would be a waste of time.  I also made sure nothing was even touching the console.

Power is a known good circuit wired by myself with the help of another licensed electrician-and both of us happen to be pretty picky about our work.  We have another system in another building physically about 200 feet away, power comes from same overhead drop as our main system and it is having no issues.  Power would be the only thing that swapping in another mixer would test, given that the testing I did was a stand alone test?

It does sound like we may have people interested in springing for a new mixer-probably as good a time for us to make the jump to digital as any and something that is already on our radar.  If that flies, we will either sell board as is or have serviced and sell.  It is too nice to scrap-it has lived in our sound booth its entire life covered when not in use primarily used by myself and one or two others.

Powers supply caps sound plausible-while they wouldn't necessarily be suspect (in my mind anyway) if the wiring is acting as antennae.  I haven't had the opportunity to do as thorough a test as Lee has suggested, but it sounds like a challenging project for some cold winter evenings.
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Steve Swaffer

Lee Buckalew

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Re: Noise/static elimination
« Reply #15 on: October 26, 2015, 08:40:07 pm »

I haven't had the opportunity to do as thorough a test as Lee has suggested, but it sounds like a challenging project for some cold winter evenings.

Most of what I suggested can be done standing at the console with headphones on (and it sounds like you have done much of it).  It's just divide and conquer. 
Testing with another temporary console would be a very good option before trying to isolate the problem to a section of the console.

Lee
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Lee Buckalew
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Jim Thorn

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Re: Noise/static elimination
« Reply #16 on: October 27, 2015, 02:38:31 am »

Stephen,

I had a noise problem with a GL4800 a few years ago.  As with yours, the noise was intermittent, and would occur without regard to the input I was soloing.  Noise appeared in headphones and at mixer outputs.  After months of chasing it without being able to reliably duplicate it, I finally got lucky.  A user reported that every input channel to the right of the master section went dead during a rehearsal, but by the time I got a look at it they were working.  Lifting the mixer an inch off the table and letting it drop would now trigger the noise, which the users had described as sounding like thunder.  When I opened the mixer up to check ribbon cables, I found discoloration of the insulation on two conductors of the ribbon cable at the insulation displacement connector of the Master section's board.

It turns out that the multi pin connector from the external power supply has fairly heavy-gauge wires feeding the Master board, but the voltages are then sent from there out to all the other boards on small-gauge conductors of the ribbon cable that runs the entire width of the mixer.  Two adjacent conductors are used for each voltage (+/- 17 volts IIRC).  Apparently the insulation displacement connection for +17 was imperfect, and over time began to heat up, discoloring the insulation and oxidizing the copper, making the problem steadily worse.  I was able to cut out a few inches of the damaged conductors, clean up the connector with Deoxit, and punch down fresh pieces of 20 gauge hookup wire, which I then spliced to the cut ends of the ribbon cable.  It wasn't very pretty, but it worked well until I was able to get a new ribbon cable assembly.

If this is what is happening with your mixer, you may be able to see a light tan or brownish cast on the light gray insulation of the ribbon cable at the master module, since that is the only place where the total current feeding all other boards must pass through two small IDC connections. 

I'm hoping that this is your answer -- it would be great if someone else could benefit from my hard-won knowledge!

Jim Thorn
I have been fighting noise on our church sound system for months.  Very erratic sometimes very minimal other times unbearable.  I have chased it and one time it seems like it is from one mic or set of mics, the next somewhere else.  I was able to eliminate (or at least greatly reduce it) for about 2 weeks by cleaning all of the jacks on the platform with De-oxit.

Unplugging nearly all of the mics at the mixer also helps-though it defeats the purpose!

Most of the mic jacks have been in place 10 years or longer and we use special effects every year at Christmas time that I can't help but think contribute to degrading of the jacks.

I have recommended wholesale replacing the jacks, but am being asked my confidence level in this curing the problem.  The mixer is an A&H GL3800.  (Which I recently cleaned ) Could there be a problem with the mixer making it more susceptible to static, or does my approach seem reasonable?
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John Roberts {JR}

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Re: Noise/static elimination
« Reply #17 on: October 27, 2015, 12:33:23 pm »

Yup ribbon cables can be problematic. If you isolate it to inside the mixer, an obvious thing to check.

JR
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Stephen Swaffer

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Re: Noise/static elimination
« Reply #18 on: November 06, 2015, 11:29:24 pm »

I often wonder the conclusion of the matter in some threads, to that end I give this update.

Installed a QU-32 last Saturday (we decided an upgrade/conversion to digital made sense in the big picture anyway and we had a couple people write checks to facilitate).  A couple hours of testing and setup, services on Sunday and Wednesday and no noise/static.  A number of compliments in the clarity/quality of sound.  Not sure if that is to be blamed on going digital, or if there was another less obvious problem lurking as well.  In any case, all is good now.  Thanks to all who took time to weigh in.

Jim, I will give the ribbon cables a thorough going over after the first of the year when (I hope anyway) things calm down a bit.  Day job is slamming me with a big deadline the same week as our annual Christmas play-both 6 weeks out so pretty much putting optional stuff on hold for a while.
« Last Edit: November 06, 2015, 11:33:16 pm by Stephen Swaffer »
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Steve Swaffer

ProSoundWeb Community

Re: Noise/static elimination
« Reply #18 on: November 06, 2015, 11:29:24 pm »


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