ground life question

[umkcprof]

Hi all. . .

 

Chalk this one up to a severely undesirable ratio of engineering expertise to resources problem.

 

In an earlier post on balanced power, "The Chinese" mentioned that I should be lifting the ground at the destination point of my XLR connections in order to reduce my noice floor to its lowest level.

 

This begs the following important two questions:

 

QUESTION ONE: What is the "destination"?

 

Let's use my set-up (as of tomorrow) for an example. Here is my EXACT signal path from microphone to AD converter:

 

1. Manley Gold Reference mic

2. XLR cable from microphone to Universal Audio 6176 preamp

3. XLR connector from the Universal Audio 6176 610B preamp (direct out, by-passing the 1176LN compressor within the 6176 for the moment)

3. XLR cable out of the preamp to a TRS connector and into a Furman PB-48 patch bay

4. TRS connector out of the Furman patch bay to an XLR connector and into one channel of an Avalon AD2055 equalizer

5. XLR connector out of the AD2055 to a TRS connector to the patch bay

6. TRS connector out of the patch bay to an XLR connector and into a Manley Variable Mu compressor

7. XLR connector out of the Manley Variable Mu to a TRS connector and back into the patch bay

8. TRS connector out of the patch bay to an XLR connector and into a Lucid AD9624 converter.

 

So. . . WHERE should the grounds be lifted? At every DEVICE (not counting the patch bay) destination point? At EVERY destination point (INCLUDING the patch bay)? Or only at the Lucid AD9624 converter?

 

IMPORTANT QUESTION 2: How do you lift the ground??? Just open up the XLR or TRS connectors and snip the wire?

 

Sorry to ask such stupid questions, but, believe it or not, I am getting some pretty nice results.

 

It should go without saying that your kind advice is always a precious gift to me.

 

Thanks so much.

 

Steve

[where02190]

Destination=input.

[Phil O'Keefe]

What Where said.

 

PS - I think you meant "gound LIFT" Steve.

[umkcprof]

Thanks for input. . . pun intended.

 

The question I have is what exactly constitutes an input? Does this mean every input to every device in the chain (including the patch bay)? Or just the last input in the chain? Or just the devices (and not the patch bay inputs)?

 

Secondly, how does one "lift the ground"? Just snip the wire? Or connect it to a different point? Which pin?

 

Finally, why on earth do they have 3 on a balanced cable if we only really use two of the wires???

 

Thanks again!

 

Steve

[rhythminmind]

as said the rule is disconnect at input...

 

then why 3 wires? 3 are still needed but thats one advantage of balanced cable only one end needs to be grounded..."single-point grounding" .. it works because all the audio gear should have a comman AC ground..

 

a lot of studio's (most that i know of) wire patchbays with this rule. they leave the input shield's off.. they do this on all devices for double protection.. the patch bays i deal with at work lift the shield and also have a tech power ground for the gear..

 

a common clean grounded power source for all your gear is needed for ground lifting to really work..

[The Chinese]

 

Originally posted by umkcprof Hi all. . . Chalk this one up to a severely undesirable ratio of engineering expertise to resources problem. In an earlier post on balanced power, "The Chinese" mentioned that I should be lifting the ground at the destination point of my XLR connections in order to reduce my noice floor to its lowest level. This begs the following important two questions: QUESTION ONE: What is the "destination"? Let's use my set-up (as of tomorrow) for an example. Here is my EXACT signal path from microphone to AD converter: 1. Manley Gold Reference mic 2. XLR cable from microphone to Universal Audio 6176 preamp 3. XLR connector from the Universal Audio 6176 610B preamp (direct out, by-passing the 1176LN compressor within the 6176 for the moment) 3. XLR cable out of the preamp to a TRS connector and into a Furman PB-48 patch bay 4. TRS connector out of the Furman patch bay to an XLR connector and into one channel of an Avalon AD2055 equalizer 5. XLR connector out of the AD2055 to a TRS connector to the patch bay 6. TRS connector out of the patch bay to an XLR connector and into a Manley Variable Mu compressor 7. XLR connector out of the Manley Variable Mu to a TRS connector and back into the patch bay 8. TRS connector out of the patch bay to an XLR connector and into a Lucid AD9624 converter. So. . . WHERE should the grounds be lifted? At every DEVICE (not counting the patch bay) destination point? At EVERY destination point (INCLUDING the patch bay)? Or only at the Lucid AD9624 converter? IMPORTANT QUESTION 2: How do you lift the ground??? Just open up the XLR or TRS connectors and snip the wire? Sorry to ask such stupid questions, but, believe it or not, I am getting some pretty nice results. It should go without saying that your kind advice is always a precious gift to me. Thanks so much. Steve

 

 

 

 

Steve-

 

A) Destination means the Input. You should lift at every input with the EXCEPTION of Microphone inputs and unbalanced inputs.

 

B) To lift, simply cut the wire going to pin 1 of the XXLR, or the sleeve of a TRS.

 

HOWEVER....

 

You have a large caveat here, in that you are using a PB-48...This bay is not a Bussable ground, which causes problem in this scheme, and very important. Without that grround bussing happening, you will not have a shield covering your signal path when it leaves the Patchbay. while this will work and pass signal, it's less than desirable for noise reasons.

 

 

-Todd A.