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oof.lucasmicrophone

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Posts: 90 Member Since: 24/01/2014

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Jan 15 17 4:31 PM

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Sounds like i need to pull my power supply and measure the outputs.  Often, but not every day, recently every pot and switch crackles.  Aux sends, EQ, and switches.  On every channel.  Pan pots are quiet as are the faders and fx send/return pots.  Mixing is limited when this is happenning-- no live eq/send adjustements.

It's an old Sound Workshop 34c desk that was completely rebuilt around 2002 or so and has been remarkably trouble-free. I would normally assume it would be dirt or leaking DC on a channel.  But the fact that it is on everything, makes me think power supply.
So, if you think this is a valid point, my question is:
 If I put a scope on the outs of the two  +/- 16v supplies (and they verify at 16v) will the scope show me noise on the rails that might be causing the scratchiness?  
--it could be dirt in the connections between the supply and the cable, and the cable to the console. so will clean those when I pull the supply out.
-- i am testing with a 100Hz tone.  With music, the knobs are a bit quieter.  switches still bark....
As a last resort, and I mean last, I will sink all 32 modules and master section in the old Ultrasonic Bath.  What a hassle that would be.  NYC is a dirty place, but this seems like more than that.
Thanks, in advance for any insight!
David

Last Edited By: oof Jan 15 17 4:40 PM. Edited 1 time

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John Eppstein

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Posts: 1,219 Member Since:31/05/2015

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Jan 15 17 4:44 PM

oof wrote:
Sounds like i need to pull my power supply and measure the outputs.  Often, but not every day, recently every pot and switch crackles.  Aux sends, EQ, and switches.  On every channel.  Pan pots are quiet as are the faders and fx send/return pots.  Mixing is limited when this is happenning-- no live eq/send adjustements.

It's an old Sound Workshop 34c desk that was completely rebuilt around 2002 or so and has been remarkably trouble-free. I would normally assume it would be dirt or leaking DC on a channel.  But the fact that it is on everything, makes me think power supply.
So, if you think this is a valid point, my question is:
 If I put a scope on the outs of the two  +/- 16v supplies (and they verify at 16v) will the scope show me noise on the rails that might be causing the scratchiness?  
--it could be dirt in the connections between the supply and the cable, and the cable to the console. so will clean those when I pull the supply out.

As a last resort, and I mean last, I will sink all 32 modules and master section in the old Ultrasonic Bath.  What a hassle that would be.  NYC is a dirty place, but this seems like more than that.
Thanks, in advance for any insight!
David

It sounds to me like something's leaking DC - or setting up an imbalance that causes DC to appear across all the controls. I'd check the voltages on all the rails. I'd be surprised if the problem was actual noise on the rails - DC across a control will cause scratchiness. Since it's intermittent I'd suspect a bad connector or solderr joint somewhere, but it could be something else.

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oof.lucasmicrophone

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Posts: 90 Member Since:24/01/2014

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Jan 15 17 6:38 PM

Hi John, thanks as always, for the helpful response. I did measure the pus and it was within .1v on each side. But I did notice a .4v drop from the supply to the master section on the desk. So I trimmed up the supply to 16.4v and now I get 16v at the desk. Not sure if.4v makes difference in operation, but it feels good.
Still have the noisey pots and switches though.
One more piece of info: There is one supply for modules 1-16 and another for 17-32. the noise is present on all modules. So perhaps it's NOT the supply, since it would be rare for both supplies to exhibit the same problem. They were last replaced in 2004 and I don't leave them on 24/7. I used to a long time ago, but now power down at the end of the day. Just as a friend told me, "whatever will blow will do it in the first couple of weeks -- after that you'll be stable." Just how it happened. And it cut my electric bill in half. More $$ for tequila.

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zmix

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Posts: 4,060 Member Since:20/01/2011

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Jan 15 17 6:39 PM

I concur, measure the rails at one of the noisy channels with a sensitive DVM and see if there is an imbalance.

Barring that, remove and individually clean each pin on the main PSU connectors..


..

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oof.lucasmicrophone

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Posts: 90 Member Since:24/01/2014

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Jan 15 17 9:02 PM

Thanks Chuck & Bark, for the suggestions. I have cleaned all pins and I'm within .2v between the rails. I did reseat the molex (Aack!) connectors in the PSU but will go back in there see what else I can clean up. I figure it has to be there since the scratchiness varies and is global. For now, I can live with fewer on-the-fly EQ changes, but I do want to figure out. Maybe Mercury is in retrograde. Or in Uranus. I don't know....

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gold

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Jan 16 17 3:11 PM

Forgive me if this is obvious but did you measure any DC across any of the offending pots? It might be easier to chase it down backwards from the pots instead of forward from the PSU.

If audio common is separate from chassis I'd see if there is DC between chassis and common.

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oof.lucasmicrophone

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Posts: 90 Member Since:24/01/2014

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Jan 17 17 3:32 PM

Thanks Paul- only insignificant DC measured at the pots. BUT.. I did figure it out this morning.. Good and Bad news. I pulled a modules and shot a bit of DeOxit into the EQ pots and they are now quiet as could be. It seems amazing that so many pots could become noisy, but in day-to-day sessions I don't really use the desk EQ's so much so I guess it just crept up on me and I hadn't really noticed the extent of the issue.
So it's time total a day or two and pull each module and either:
1. DeOxit each pot
2.take them to the spa up the street where they can get a nice soaking in the warm ultrasonic bath. Pedicure-- no extra charge.

Thanks for the advice guys-- sorry it turned out to be so pedestrian. It's been more than 10 years so time for a good cleaning.

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oof.lucasmicrophone

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Jan 17 17 9:14 PM

not that this hasn't been debated since the times of Spartacus, but...is there an issue with DeOxit D5 for cleaning switches and pots? Some say it leaves too much of a residue. so maybe using a blast of compressed air afterwards?. I also have a can of MG Chem Electrosolve zero residue here so that is an options,( to be followed by a bit of lubricant?). I will make enough downtime and do the entire desk so I'd like to be sure I'm using the best solvent on the pots specifically. I've used D5 for ages on pots here and there, but never for a whole desk.
Thanks

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John Eppstein

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Posts: 1,219 Member Since:31/05/2015

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Jan 19 17 5:15 AM

oof wrote:
Thanks Paul- only insignificant DC measured at the pots. BUT.. I did figure it out this morning.. Good and Bad news. I pulled a modules and shot a bit of DeOxit into the EQ pots and they are now quiet as could be. It seems amazing that so many pots could become noisy, but in day-to-day sessions I don't really use the desk EQ's so much so I guess it just crept up on me and I hadn't really noticed the extent of the issue.
So it's time total a day or two and pull each module and either:
1. DeOxit each pot
2.take them to the spa up the street where they can get a nice soaking in the warm ultrasonic bath. Pedicure-- no extra charge.

Thanks for the advice guys-- sorry it turned out to be so pedestrian. It's been more than 10 years so time for a good cleaning.

DON"T USE DEOXIT!

It contains lubricants that will catch and hold dirt particles and will cause a return of the problem, Use a cleaner that does not contain lingering lubricants. My Studer tech recommended one by Miller-Stephenson that does a great job,. I don't remember the number offhand but I'll look for it in the (relative) morning and post it here.

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soapfoot

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Posts: 7,311 Member Since:04/02/2011

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Jan 19 17 6:58 AM

on the other hand, pots NEED lubricating because if you don't, the conductive material can scratch and flake off (particularly in older carbon pots), which creates dust that makes it scratchy again.

brad allen williams

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oof.lucasmicrophone

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Posts: 90 Member Since:24/01/2014

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Jan 19 17 11:01 AM

This is what I find so interesting. Concerning Cleaing solvents there seems to be no consensus on what's best. Even reading through the Sticky, it's clear that everyone has a different experience. I agree that pots want lube, yet that same lube attracts dirt. But don't they come lubed when they're new? Can you operate them without lube and not have loose-feeling pots that will eventually pit themselves from the scraping?
Hmmm...

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zmix

Aqua Marine

Posts: 4,060 Member Since:20/01/2011

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Jan 19 17 3:41 PM

oof wrote:
This is what I find so interesting. Concerning Cleaing solvents there seems to be no consensus on what's best. Even reading through the Sticky, it's clear that everyone has a different experience. I agree that pots want lube, yet that same lube attracts dirt. But don't they come lubed when they're new? Can you operate them without lube and not have loose-feeling pots that will eventually pit themselves from the scraping?
Hmmm...

The "lube" should be on the shaft, not the conductive track.


I think this is a fascinating comparison, have a look and see what you think:






...

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gtoledo3

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Posts: 4,110 Member Since:23/10/2013

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Jan 19 17 7:10 PM

Compressed air can get you really far sometimes ... referring to that vid, not the original thread post necessarily.

I bet if he had given the compressed air fader another blast, or maybe exercised the fader a few times more times after, that little gap might have gone away.

I wondered after seeing that tape the first time why he didn't try compressed air, then the lubricant, so that he isn't gumming up a bunch of dust right off the bat. I have done it in that order since seeing the vid when lube is needed, since it got me thinking about it more.

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zmix

Aqua Marine

Posts: 4,060 Member Since:20/01/2011

#15 [url]

Jan 19 17 9:37 PM

gtoledo3 wrote:
Compressed air can get you really far sometimes ... referring to that vid, not the original thread post necessarily.

I bet if he had given the compressed air fader another blast, or maybe exercised the fader a few times more times after, that little gap might have gone away.

I wondered after seeing that tape the first time why he didn't try compressed air, then the lubricant, so that he isn't gumming up a bunch of dust right off the bat. I have done it in that order since seeing the vid when lube is needed, since it got me thinking about it more.
I think what he did was representative of the methods typically used by most techs. 

What's particularly valuable is that he demonstrated the relative effectiveness of these methods. 


(and, also,  I thought it was fairly obvious how each method could be adapted to improve the efficacy for any given symptom.)



...

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