Distribution amp for headphones?

[ledogboy]

Hey Gents-
I have a nagging issue at my studio with ground noise in the headphone distribution system.  It is the only ground noise issue I have (the studio is well wired, with an isolation transformer between it and the outside world), and I strongly suspect that the issue is caused by the half assed way in which HP sends were wired.  There are eight sends in the console pachbay that go out to five different HP patch panels in the various live/iso rooms.  There are four stereo jacks in the HP patch panels, so the eight sends are being sent as pairs with a shared ground and two hots (we use mixer/amps, so all eight mono feeds are often used).  All five snakes meet the console wiring such that (for instance) HP send 1 and 2 is wired from the console to channel 1 and 2 of all five snakes.  If I bypass this wiring and patch from my aux (or PT) outs directly into the HP amp, there is no hum- even if I use an extension cord and plug the ac into any of the other rooms.

I am thinking that getting rid of the kludged wires and using an old broadcast distribution amplifier might be my ticket to hum free headphones.  I have also considered installing an entirely new HP system (ala Furman), but other that the hum, I am perfectly happy with what we have, and I would hate to have to re-wire (the cable is through-wall, and not in conduit).  Any thoughts?  I see a number of reasonably priced old ADA's on ebay, but I'd hate to throw money away without a reasonable expectation of success.  Any input is greatly appreciated!

Cheers,
Ryan

 

[ledogboy]

Eh, what the hell.  Distro amps were so cheap on ebay I decided to just give it a whirl.  If it doesn't help my current situation, I can use it for something else!

 

[Matthew Jacobs]

Not sure a DA will help, but please let us know if it works. I think a DA would increase the signal to noise ratio therefore pushing the humm down in level maybe? don't know?

I think it would be best to fix the wiring so that it can be balanced.

Transformers might help your current situation, but that's an expensive option.

 

[ledogboy]

Hey Matthew-
Thanks for the reply.  I actually tried switching the sends to four balanced, rather than the current configuration, to no avail.  I also tried putting transformers between the desk and the send snakes to little or no effect.  I'm going to play around with the console tomorrow and see if I can't find a solution.  I'll keep you posted!
Cheers,
Ryan

 

[pucho812]

you should be using balanced connections  for as much of you connections as you can. As for balanced to unbalanced and making cables read this rane note. It will help you out.


http://www.rane.com/note110.html

 

[0dbfs]

So, do you get hum if you send just one balanced channel out to the studio over that installed snake? How about if you keep everything the same but run a dedicated "balanced-test-cable" out to the studio to the HP amp?

Cheers,
jonathan

 

[fazer]

You refer to mixer/amps.  Does that imply the use of a mixer like a mackie or something.  If so you need to balance to float the ground to the mixers.  You could have a loop between mixer stations.   

Also we have a Amek/Mozart console at work.  People get hum on the headphones when they turn up the master on the console and don't drive the sends on each channel loud enough.  The solution was to lower the gain on the headphone/amps and drive the channels louder and turn the master mixer on the console to about 50%  This made for a unity gain with low noise from the headphone amps.