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How to fix a ground loop issue with Avalon AD2022?
Old 30th January 2013
  #1
Gear Addict
 
🎧 5 years
How to fix a ground loop issue with Avalon AD2022?

I have recently purchased an Avalon AD2022 preamp and I am experiencing a ground loop issue with the device. I have the Avalon connected to a Samson TRS patchbay via balanced XLR output, and from the patchbay into my RME UCX interface via TRS.

I am hearing low humming noise on the headphone output of my D-BOX when I have the Avalon turned on and connected to the UCX.

What is the best solution to fix the ground loop issue and get rid of the hum in this case?
Old 30th January 2013
  #2
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savyurrecords's Avatar
 
🎧 10 years
The only solution is through troubleshooting. You have to isolate the problem.

First thing I would do is patch the preamp directly to a monitor system, such as a powered speaker. Then listen is there a hum? Yes? Change the input source, Change the cabling, Still there? Yes. Well it looks like the Avalon box has an issue.

If you did not hear a hum then your problem could be in the patchbay/wiring or the audio interface. Then you have to add one piece back at a time till you hear the hum.

Electrical hum can be a tricky issue and can sometimes seem to have a mind of its own. Keep working at it and you will fix it.

I understand it is just a patch bay but why are you patching that nice Avalon through a Samson patch bay? Do you have to do this?
Old 30th January 2013
  #3
Gear Addict
 
🎧 5 years
I have already tested extensively and narrowed down the problem to the Avalon preamp output ground loop issue.

I have been instructed to "lift the shield (pin 1) of the male side of the output cable coming from the Avalon to the interface", but I am not quite sure what does that mean - especially as I am connecting the Avalon to a TRS patchbay and from there into my audio interface and/or outboard gear.
Old 30th January 2013
  #4
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savyurrecords's Avatar
 
🎧 10 years
Well you didn't say that you had narrowed the problem down. That bit of info would have saved me a bit of typing. ....

Ok ground lift is easy. On your XLR connector on the cable that is connected to the output, take the shell off and look for the wire connected to Pin 1. It will most likely be the only wire you see without a insulator around it. The pin 1 labeling will be hard to read but it is definitely there. Now get a pair of cutters and clip this wire, it is the ground. Now put the connector back on and label the cable so you remember what you did.

If it were me I would get the soldering iron and a desoldering tool disconnect the wire that way. But clipping works just fine.

How is the patchbay grounded? Are the grounds all tied together or isolated?
Old 31st January 2013 | Show parent
  #5
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by savyurrecords ➑️
Well you didn't say that you had narrowed the problem down. That bit of info would have saved me a bit of typing. ....
Well, if you would have read the topic

Quote:
Originally Posted by savyurrecords ➑️
Ok ground lift is easy. On your XLR connector on the cable that is connected to the output, take the shell off and look for the wire connected to Pin 1. It will most likely be the only wire you see without a insulator around it. The pin 1 labeling will be hard to read but it is definitely there. Now get a pair of cutters and clip this wire, it is the ground. Now put the connector back on and label the cable so you remember what you did.
As I am using a female XLR to TRS cable going from Avalon (XLR) to the patchbay (TSR), am I supposed to do this procedure on the TRS end of the cable, or the female XLR end?

Quote:
Originally Posted by savyurrecords ➑️
How is the patchbay grounded? Are the grounds all tied together or isolated?
I am not sure if it is grounded or not, the model I am using is Samson S-Patch Plus and I have it set to "thru" mode.
Old 31st January 2013
  #6
Gear Guru
 
matt thomas's Avatar
 
🎧 15 years
The TRS end, but both ends will work. Remember to clearly label the cable that you do this to!

I'm not sure why you're going via the patchbay at all. You should just go straight to the interface, assuming you are not actually patching anything.

matt
Old 31st January 2013 | Show parent
  #7
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by matt thomas ➑️
I'm not sure why you're going via the patchbay at all. You should just go straight to the interface, assuming you are not actually patching anything.
I'm going via the patchbay so that I can run the preamp thru my Dangerous Bax EQ and/or Manley Vari-Mu when needed.

Quote:
Originally Posted by matt thomas ➑️
The TRS end, but both ends will work. Remember to clearly label the cable that you do this to!
Ok, good to know. Will need to seek some instructions on how to do the ground lift on a TRS connector then.
Old 31st January 2013 | Show parent
  #8
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matt thomas's Avatar
 
🎧 15 years
Quote:
Originally Posted by devastat ➑️
I'm going via the patchbay so that I can run my preamp thru Dangerous Bax EQ and/or Manley Vari-Mu while tracking when needed.



I will have to seek some instructions over the net on how to do the ground lift on a TRS connector, I have no idea how to do this..
Oh I didn't know you had those other pieces to patch in. You could also permanently have them inline, and use their bypasses? Unless you use them on other things as well.

You might want to look up "star grounding". There is a decent amount about it at the beginning of the Toft ATB manual that you could download just to read. Also be aware that it can be dangerous if something goes wrong and some current needs to find its way to earth. So do it properly, and do so at your own risk. Ideally, it should get rid of (most) ground loops.

You'll want to lift the "S". This is the sleeve, or the part of the cable that wraps around the other two wires in the cable. (note how it is also labelled as "ground" in this diagram)



Matt
Old 31st January 2013 | Show parent
  #9
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by matt thomas ➑️
Oh I didn't know you had those other pieces to patch in. You could also permanently have them inline, and use their bypasses? Unless you use them on other things as well.
I'm also using them for mixing and mastering via my D-Box so I guess that patchbay is still the best solution in my case.

It looks like it might best for me to order such cable from Redco, as I don't have any experience on soldering cables yet..

Thanks a lot for your help, really appreciated!
Old 31st January 2013 | Show parent
  #10
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matt thomas's Avatar
 
🎧 15 years
Quote:
Originally Posted by devastat ➑️
It looks like it might best for me to order such cable from Redco, as I don't have any experience on soldering cables yet..
Just open the plug and snip through the sleeve wire attached to the Sleeve of the plug. Make sure that none of it still connects or touches anything else, and you're done. After putting the plug back together of course.

matt
Old 31st January 2013
  #11
Gear Addict
 
🎧 5 years
Ok, i'll try that!

P.S there is no danger I might accidentally fry my Avalon preamp or RME UCX if I do it wrong?
Old 31st January 2013 | Show parent
  #12
Gear Guru
 
matt thomas's Avatar
 
🎧 15 years
Quote:
Originally Posted by devastat ➑️
Ok, i'll try that!

P.S there is no danger I might accidentally fry my Avalon preamp or RME UCX if I do it wrong?
I wouldn't like to 100% guarantee that there is NO danger, in case there is something I haven't thought about. But I can't think of any reason it could be bad if this is all you do.

I would do it if it were my own.

If you want, you could email Avalon to ask what they think.

matt
Old 31st January 2013 | Show parent
  #13
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by matt thomas ➑️
I wouldn't like to 100% guarantee that there is NO danger, in case there is something I haven't thought about. But I can't think of any reason it could be bad if this is all you do.

I would do it if it were my own.

If you want, you could email Avalon to ask what they think.

matt
Ok. I'll give it a try
Old 31st January 2013
  #14
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matt thomas's Avatar
 
🎧 15 years
Old 31st January 2013
  #15
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matt thomas's Avatar
 
🎧 15 years
ps. Just remembered, it can cause a level drop in a small number of situations, but I forget where.. you might want search for that..

m
Old 31st January 2013 | Show parent
  #16
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by matt thomas ➑️
ps. Just remembered, it can cause a level drop in a small number of situations, but I forget where.. you might want search for that..

m
Ok, I'll do that. Tho, I might just go for it and compare the cable with normal one and see if there is a level drop.

My temporal solution so far has been removing the D-Box (that I use for monitoring) from the rack, it also removes the hum..
πŸ“ Reply

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