patchbay noise

[moogerfooger]

I added a couple ADC patchbays to my humble personal studio, and love the flexibility. they are 1/4" with the remote punchdowns - normals brought out to punch panel. I got them from Bobby Hickey so they are in perfect woking order but used. the system is dead quiet when using balanced gear, and some unbalanced line level stuff but my triton hums to beat hell. if I plug it straight into the mixer it is as quiet as a triton gets. my runs aren't terribly long and the wire is of good "live sound" quality but not mogami mulit pair- if you know what I mean. the hum is not too noticable when no channel gain is applied at the mixer, but still not acceptable. I find my self writing/arranging through the patch bay and going straight in when tracking-- this defeats the purpose of the bay -not to mention the frustration from having put ALL that time in wireing them up- I'm thankfull for any and all suggestions / tips - etc

[Paully]

Sounds like you've got a ground loop. They're a bitch to isolate, but read this thread. You might get your answer.

 

http://gearslutz.com/board/showthread.php3?t=47084

 

Paul

[Paully]

Mooger,

Gotta say, it sounds like the patchbay is the problem. It might help if you explain the wiring more completely. Try disconnecting the shield at the board first, as you suggested. If no luck, try at the PB side.

 

At the PB:

* Are the channels all 1/4" balanced(TRS) or unbalanced(TS)?

* What board points does it connect to: mic or line in? A stereo synth is usually connected to the 'line in' if 'line in' is a balanced input. I'm not sure why you would want a regular mic input to be normalled if the PB is just there to bring the input out front for access. In that case, you need to 'open' the normalling structure at that PB channel only. Use the 'return' jack(front) direct to 'out' jack(rear), then connect that to the board. Don't even use the rear 'input' and front 'send' jacks. Normalling is used for interrupting a signal.. not what you want!

 

At the Triton:

* Is it a single, unbalanced out? or

* Is the output two independent mono jacks (L and R), or a balanced stereo output on a single stereo jack? In the latter case, a simple 1:1 centertapped isolation transformer might work.

 

Don't be too proud to try one of those 3 to 2 prong groundlift cubes that RadioShack sells on the Triton's AC plug. It just might work, and we all use 'em. Keep us posted.

 

Paul

[The Chinese]

Originally posted by moogerfooger Paul -- that was it -- all I had to do was jumper the sleaves on one pair of points -- 1 and 25-- and all 6 triton channels are quiet as a mouse -- there was no ground at all -- let alone a loop. Thanks for letting me bounce this off you. I was beginning to think I was crazy

 

Mooger...I meant to hop here earlier, but glad to see you got it working.

 

What this means is that your PB's are what's called Isolated ground. Each jack is set up independantly and is "isolated" There is never any normalling for ground in a patchbay, thus the reason you have to jumper it through. Many bays come as bussed ground, or looped ground (in essence what you are doing...)

 

Here's a pearl i want to pass on-

 

The real solution here is to balance the line outs of your Triton to +4dbu Balanced. You have a band-aid right now, but it could cause you problems in the future if/when you expand your studio. Also, for analog audio, i feel it best to buss the grounds of your patchbays, and then take that ground to be your star point. hit me back if you want more info.

 

-Todd A.

[Paully]

Mooger,

 

Congrats. After reading about the unnormalled rings, I was going to get back and suggest normalling all points on one channel as a test. Then I read your subsequent posts. Glad to see that worked. One other point that you're not going to like.

On your service grounding, NEVER use more than 1 ground rod, and make sure the one rod is near the main breaker panel and vertically driven. People assume that extra rods are a good thing, but the only thing that accomplishes is setting up the possibility for new ground loops. Instead, use a really heavy guage romex with a thick drain wire from the sub to the main. Trust me. This I really do know.

 

Paul

[Kiwiburger]

Installing a second ground rod and connecting to your electical earth is a recipe for hum - i've just been there and done that.

 

If your new ground rod is better than those in your neighborhood, you can attract more ground noise your way - this was extremely noticable at my place.

 

Replacing my electrical earth with my new ground rod yielded the biggest gains: dead silence compared to about a 60dB hum I used to have. (I had a serious problem of 1.5 volts AC square wave on my electrical ground. I could drive an 8 ohm loudspeaker quite loud with the potential difference between "electrical earth" and a real ground stake of any description.

 

So if you have two ground spikes, and one is better than the other (moister earth, newer etc) then you will get an AC ground loop hum that will drive your unbalanced cables crazy, because that's supplied direct to your shields.

[Paully]

 

Originally posted by moogerfooger ...however the neutral of the subpanel is still connected the ground of the main panel. so yes I still have 2 paths to ground -- the main panel ground is suspect IMO due to the fact that it is up against the foundation buried in gravel. Should I 1. go back to just using the main panel ground and hope for the best 2 use the ground from the studio as the house ground 3 install a new rod as close to the main panel as I can get it due to the fact that the main panels earthground is now covered by the cement padio and the main panel is roughly 12 feet from the corner of the basement, and the padio goes the whole legnth of the back of the house I will have to sink a rod about 13 to 15 freet from the panel the only real hum left is comming from my general use computer's audio out, but its only used for itoons and internet and such--- My DAW is dead silent.

 

Mooger,

 

Leave your sub's drain connected only to the mains, not the secondary rod. Get rid of it. Use both of your suggestions 1 and 3; NOT 2. Look at it this way. The street transformer supplying your power also has a drain wire that goes from the top of the pole to the bottom, then to ground. That's a 30-40 foot run with no problems. The purpose for grounding the main box is simple; that's where most of the house power is drawn from, and the stronger drain is needed there. Also, if you made the sub's rod

the primary, you would have to run a REAL heavy drain to the main box to cover the main's heavier needs. A single 8-10' rod at the main's location is plenty.

 

Paul

 

By the way, I archive articles on power distribution. If you want, I can PM you an attachment that will explain 'how to do it' in detail.

[Kiwiburger]

I guess your Triton has a three prong ac plug with a real earth, and the unbalanced stuff that doesn't hum just have two prong?

 

If audio gear is grounded by two seperate paths (via the electrical ground, and via the audio cable shields) you can get ground loop hum. Have you tried lifting the shield connection at one end of the unbalanced cable?