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  #1  
Old 09-06-2020, 05:00 PM
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Southsidemusic Southsidemusic is offline
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Default Going insane with hum from patchbay units NEED Your Help!

Hi Friends

I am going insane with this issue we are having now.

Background info and explanation:

Bought a crapload of new analog gear for the big room lately and now we have soo much analog toys we tend to turn off a few of the racks as the power needed to run all that is enough for a small village.

So everything has Neutrik connections and Mogami cables attached into 3 balanced patchbays of high quality.

The issue:

When we powered off the racks and only have say one rack filled with gear ON but the other racks which have all the gear turned OFF but still have some units in those racks patched into the Patchbays (with the units power OFF) we get a damn HUM low irritating as hell.

We tried all the tricks like swapping power outlets, checking cables and all that and every piece of gear in our studio goes into a seperate socket in the power conditioners and not one analog synth or outboard share sockets in the power units.

The weird thing:

When we power ON the units that are patched in and cause the hum noise the hum and noise disappears.

So in conclusion:

If we turn ON ALL the outboards and the same patch settings kept no noise at all but as soon as we power off the units still patched in the bayw some make a low noise hum like 1176’s, Neve 1073 pre’s, WA Buscomp, Bluestripe Rev A and Rev F
But not say Monster-2, WesAudio NG_Nuscomp, LA2A’s, Manley Comps and 500 series units etc etc etc ...

The culprits patched in but turned OFF like some pres and comps make the humming noise and as soon as we either pull out a patch cable or turn ON these units the humming is gone!

We never noticed before as all the studio runs off the same outlets so everything has been ON all the time which made the hum not there. But now with soo much gear we started turning off some of the units and racks and kept some patched in to the balanced patchbays and thats when we noticed that some units makes this humming sound until we either turn on the units or pull out the patch cable connection.

Does anyone here know why this only affect some outboard units and why the humming appear only when turned OFF and patched in and why other units doesn’t do this even though they are also patched in and turned OFF and why it disappeared when we turn these units ON again?

Thanks a million for any help as we googled and asked ans looked into verything we know like swapping cables in the patchbays and on the non humming units to the humming ones and vice versa but still only the same 8-10 units make this humming noise only when OFF patched in and stop of we unpatch or turn the. On.

All the best and let me know if more info is needed as I am going crazy for real and my stomach pain is maxed now.
Some units
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  #2  
Old 09-06-2020, 05:39 PM
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Default Going insane with hum from patchbay units NEED Your Help!

Off doesn’t mean the power supplies are completely decoupled. Often, one side of the power transformer is still hot as the makers of older gear weren’t necessarily concerned about putting the power switch on the hot leg from the wall. Capacitive coupling to ground will allow a small current to flow which could be a possible source of your issue. In the old days before grounded and polarized power plugs, the way to find the right way to orient the plug was to measure the chassis voltage with the plug both ways. Sticking to the orientation with the lower voltage was how you assured the lowest noise.
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  #3  
Old 09-06-2020, 06:46 PM
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Southsidemusic Southsidemusic is offline
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Default Re: Going insane with hum from patchbay units NEED Your Help!

Wow

Thank you for the explanation but some units are ”New Old Versions” like the Blue stripe and the Neve preamps. Maybe they stuck to the same power suppliew and build for the UA Teletronix and Rev A and Rev F ....

So you mean that the humming could be the units still having some contact with the racks and we patchbays hence maning a humming even though they are off? And patched? The weird headscratching for us is the second we remove the patchcable from either In/Out hole the humming stops or if we turn on the units they stop humming hehe ... very very strange ..

Have you ever seen this behavior before or has anyone else here seen this IRL?
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Old 09-06-2020, 06:55 PM
Darryl Ramm Darryl Ramm is online now
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Default Re: Going insane with hum from patchbay units NEED Your Help!

Important point from James.

Simplify! Start unplugging interconnect cables and have only one connection to a box/rack that cause a problem. Then unplugging mains cables on the problem box/rack and see what happens.

There are other things that can cause issues. Some devices etc. might do bad things when when the device is not powered on. ... even differential output devices, might not really be, and/or you might not have the common mode rejection you think you do. Narrow it down to actual devices.


BTW time to celebrate again one of the best documents on hum and ground loops: https://web.mit.edu/jhawk/tmp/p/EST0...ps_handout.pdf
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Old 09-06-2020, 07:00 PM
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Default Re: Going insane with hum from patchbay units NEED Your Help!

This is awesome info Darryl!

Snd James Huge thanks to both. Will read up on this and try to eliminate as much as possible.

The joys of Analog gear hehe
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Old 09-06-2020, 07:18 PM
Darryl Ramm Darryl Ramm is online now
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Default Re: Going insane with hum from patchbay units NEED Your Help!

What chassis or external power supplies you are running the Neve preamps with? That's one thing I'd be checking. And a problem there could affect all the modules.
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Old 09-06-2020, 07:24 PM
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Default Re: Going insane with hum from patchbay units NEED Your Help!

They are neve dpa’s 19” rack units. None of all our 500 series are affected.


For the 500 series gear we have the WesAudio NG_Titan total recall chassies and two of them with HUGE powersupply. They are like 1300 USD each and super purpose built so they are not making any hums or noise, only the Bluestripe Rev A and Rev F and the WA Buscomp along with the Neve’s. All 19” racks.
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  #8  
Old 09-06-2020, 07:31 PM
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Default Re: Going insane with hum from patchbay units NEED Your Help!

Not discounting Darryl’s pointing towards grounding, but let’s stay focused on this. The issue doesn’t happen when everything is on, only when some things are turned off and still patched. Your grounding scheme isn’t the issue.

What might alleviate the problem is making sure all of your power circuits used for your gear on on the same phase. They don’t all have to on the same breaker, just the power phase should be the same.

I would also use external power switches for all the old gear or any gear you suspect is switched on the neutral side of the power. Something like this:

https://www.amazon.com/ADJ-Products-.../dp/B00KFZ98YO
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  #9  
Old 09-06-2020, 07:48 PM
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Default Re: Going insane with hum from patchbay units NEED Your Help!

Thanks James,

Yeah when we built the rooms we had it done by pro’s so made sure the analog rack units are now And will be as we add more and more are on the same phase to avlid ground loops etc.

Another weird mindblower is this hum / noise is still there if we pull the power gables out of the units causing the noises.

Patched in but turned Off = noise
Patched in no power cable = noise
Powered on patched in = no noise
Powered Off and not patched into patchbays = no noise

So this is only evident when not used as they are super quiet when they are On and in use or not used but On and patched in. No noise if they are On but not patched in of course.

Cant wrap my mind around this issue but if this is the way things works sometimes when patched in and turned off then we will have to keep them all On or drag out a patchcord, no biggie but would be great to know for sure that this is just the way it is or if there are things we can do to avlid having to unpatch everytime we dont use something thats turned off.

PS All the gear we have which is alot is on those type of switches and all connected to 8 power conditioners each with separate socket, no unit share a input socket on the power conditioners.
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  #10  
Old 09-06-2020, 08:00 PM
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Default Re: Going insane with hum from patchbay units NEED Your Help!

Quote:
Originally Posted by Southsidemusic View Post
Patched in no power cable = noise
In that case, external switches won’t help.

What happens if you unrack a unit that gives a hum and leave it patched with no power cable and not sharing the chassis ground through the rack. Still get a hum?
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