The Grounding of Patchbays

[trodden]

The following is true for everything except when talking about mic signals-
It is good to lift the shield at some point of your signal path to avoid ground loops, but you have to be consistent about it (only at the inputs, or only at the outputs, or at the patch bay...). The idea being that there should be a ground connection for the shield for the whole path, but not connecting the chassis of the the two devices.
If you lift the shield at the inputs, the grounding of the shield will happen at the output of a device, providing electrostatic protection for the entire cable/patch length.
The tricky part comes with the equipment, and the various balanced/unbalanced connections. Once you decide on a plan, you may have to wire the gear in differently depending on how things will typically be used.
As far as the ground bus on the patch bay. Ug. The ideal patch bay will have the tip ring and sleeve isolated from anything else. It should not be where grounds tie together. You want to emulate connecting things together like you would without the patch bay, one cable going from output to input. The patch bay should only to be an extension of the connections on the back of the equipment.
Does that make any sense?

this is helping out alot.

so when building the patchbay that goes from pre amps to A/D, i should not connect the drain wire to the connectors that will be sending signal from the pre into the converters. correct?

on the bay i've halfway got together, where my compressors and effects will terminate, I should go back and cut the drain wires that i soldered to the connectors that will inserted in the inputs of those devices, correct?

now i jus got to figure out what kind of grounding scheme the guy who build my bay that goes from D/A to my board. Its kinda messy and confusing. Maybe i'll luck out and whatever he did, will agree with the lifting of the ground at the inputs that i will be using.

You want to emulate connecting things together like you would without the patch bay, one cable going from output to input. The patch bay should only to be an extension of the connections on the back of the equipment.
Does that make any sense?

THis is exactly how i envision it. WHich is why i'm still a little confused why you would lift the ground on one end. You don't have to worry about that when just using a cable between an outbput and an input.

[gregnrom]

You want to emulate connecting things together like you would without the patch bay, one cable going from output to input. The patch bay should only to be an extension of the connections on the back of the equipment.
Does that make any sense?

THis is exactly how i envision it. WHich is why i'm still a little confused why you would lift the ground on one end. You don't have to worry about that when just using a cable between an outbput and an input.

Lifting the shield is so that you don't have a chance for a ground loop. If one piece of gear is plugged in to another, across the room, in a different outlet, you can have a slightly different ground reference. That will cause hum.

so when building the patchbay that goes from pre amps to A/D, i should not connect the drain wire to the connectors that will be sending signal from the pre into the converters. correct?

If that ground bus wire is removed...
At the patch bay you should have all the TRS connections made. Lift the shield on the connectors to the equipment.

on the bay i've halfway got together, where my compressors and effects will terminate, I should go back and cut the drain wires that i soldered to the connectors that will inserted in the inputs of those devices, correct?

However you do it, at the inputs or outputs, just make sure that whenever pieces are plugged together, the shield has one path to ground.

now i jus got to figure out what kind of grounding scheme the guy who build my bay that goes from D/A to my board. Its kinda messy and confusing. Maybe i'll luck out and whatever he did, will agree with the lifting of the ground at the inputs that i will be using.

You should give yourself a nice blank slate, and clean up that bay. It will be a big pain to have to go back and fix it after everything is installed. Don't move into the house before you're done painting.
It is always easier to add or subtract the ground on the connectors for the equipment. So if your soldering/wiring your patch bay, and it is a pain, make it neutral, and include the individual ground terminations.
Strapping all the grounds together at the patch bay (with that buss wire across all the sleeve connections) can cause you problems.

[honkyjonk]

Hi Greg,

Okay, see, this is sort of what I was getting at (trying to imagine the patchbay as if there were no patch bay,) At the very least, to me, this makes things a lot more simple to think abut and to try and come up with some scheme.

So, just to re-iterate, is the scheme you're reccomending this?:

With all balanced inputs on every piece of gear, (excluding mic level inputs i.e. preamp ins) disconnect the shield of the cable that is connected to that input.

In this way, with every connection, anything following the path of the shield goes only 1 way: back to the ground of the output the said cable is connected to.

This makes a lot of sense to me, so I hope this is what you're saying.

Now, what get's more tricky, seems like, is how to interface balanced with un-balanced gear, especially when using balanced cable.

I just bought a new board and have a few un-balanced connections to wire up, so I'm planning on trying to follow what these guys are saying:
http://rane.com/note110.html
They sure are sure of themselves . . . .

[inverseroom]

Wow--a girlfriend who desolders. Man, I knew she was right for you from the start...

[gregnrom]

Hey honkyjonk,
Unbalanced gear is where compromises can occur.
If you're lifting all the inputs, on unbalanced ins, have the (-) wire terminated to the sleeve (in a tip-sleeve 1/4" connector), and float the shield. Unbalanced outs should have the shield and the (-) conductor tied together, terminated to the sleeve. There typically isn't a way isolate the ground in an unbalanced to unbalanced connection. Some gear have the option of connecting to audio ground, and chassis ground, usually a barrier strip connection. In that case, you can connect shield to the chassis ground, (-) to audio ground, and (+) to audio on the output (no shield connection on input).
The wiring recommendations on that rane page are ideal if your signal patch never changes. If that were true, you wouldn't need a patch bay. Our problem is that we need to be able to change our routing whenever we want without hum.
Greg

[honkyjonk]

Hi Greg,

Okay, now I'm going to be tackling this realistically as I just got a new board today.

The board's literature tells me to star ground everything to the board "since generally everything is connected to the board"

However, this just isn't true. Patching directly from external preamp outs to the recorder happens on a regular basis, not to mention a bunch of other possibilities.

So, I think the scheme will be to disconnect the shield on all balanced inputs to start with. That's easy.

Now, the only unbalanced connections that are going to be wired to the patch bay are the board's direct outputs and my plate reverb.

With the direct outputs, I'm wondering how to connect these on both the 1/4" end and the patch bay end. These could possibly be patched to balanced inputs on the recorder or to a balanced input on a compressor, or to an unbalanced input on say, a Bitreman or something external that has a wall-wart. So many options.

Since the wire I'm using and likely the connectors are stereo this makes things even more confusing.

(I also remember there being something funky about the Distressor being hooked up to unbalanced gear. I'm gonna have to dig into it's manual to figure that out. But this is a side issue)

As for the plate reverb, it is far enough away that I might just make a box with 3 transformers in it. 1 input, 2 output so I can run a balanced line the whole way.

But for now, it'll most often be patched (or directly wired) to a balanced aux send and be coming back into a balanced line in. So, in this regard, I'll definately just follow the instructions in your last post unless you have any other ideas.

For the board D.O.'s, let me know if this is how you'd hook them up-
1/4 out on board:

-connect hot to tip on TRS
-connect shield to shield on TRS
-connect the cold wire to the ring, then tie ring to shield (sleeve)

And then at the patch bay end connect them exactly the same? Or different?

Thanks for all the helpful info so far.

[Seamonster]

I'm by no means a grounding expert, but intuitively it's hard to imagine a patch bay which doesn't simply pass signal as though it were a single cable as ever being beneficial.

Meanwhile, the UCSC article linked on the first page of this thread states: "Unfortunately, many [Uninterruptable Power Supplies] use high frequency switching circuits and provide very dirty power. They should be keep out of the studio."

I've not heard this before, and would like to know how real a problem this is these days. What would the audible symptoms be?

I have a few of my gear's rackmounted power conditioners connected to the same heavy-duty APC UPS that my computers are on. (Power fails in my neigborhood every month or two; driving into power poles while drunk seems to be a sport around here.)

I don't notice any symptoms by doing it this way. However, I do have hum issues that come and go -- I'll have a little hum for a few days, then it will go away, then it will show up briefly a few weeks later. My best guess is that, while I do have my power and audio cables tied and routed separately, gear does get moved around sometimes, so maybe an audio cable will get jostled too close to an AC cable without my noticing, then it will get moved away again. There are no household appliances on this leg of the AC. This is the sort of intermittent voodoo that's tricky to troubleshoot.

Hoagie

[honkyjonk]

Hoagie,

You should do a search concerning the UPS boxes. I think folks will use the really good ones but the cheaper ones have the tendency to be feeding your gear what is essentially a square wave. From what I've heard though, this isn't a problem for computers as much as it is microphone power supplies and other analog gear.

But please don't quote me on this. I'm completely going from memory. And I don't understand it fully.

I think though, that there are really good UPS options, but that they are big, heavy, and cost lots of money.

[honkyjonk]

By the way, concerning my post a couple posts ago, I think my scheme is pretty much to try and have the patch bay only be passing signal, but passing the signal in the right way, and a way that doesn't cause a ground loop is what I'm concerned with.

At this point, I don't have any intentions of creating a star ground and then grounding that to the board.

[trodden]

Hey honkyjonk,
Unbalanced gear is where compromises can occur.
If you're lifting all the inputs, on unbalanced ins, have the (-) wire terminated to the sleeve (in a tip-sleeve 1/4" connector), and float the shield. Unbalanced outs should have the shield and the (-) conductor tied together, terminated to the sleeve. There typically isn't a way isolate the ground in an unbalanced to unbalanced connection. Some gear have the option of connecting to audio ground, and chassis ground, usually a barrier strip connection. In that case, you can connect shield to the chassis ground, (-) to audio ground, and (+) to audio on the output (no shield connection on input).
The wiring recommendations on that rane page are ideal if your signal patch never changes. If that were true, you wouldn't need a patch bay. Our problem is that we need to be able to change our routing whenever we want without hum.
Greg

Ok, new question. What about unbalanced outs to balanced gear situations. My Aux sends on my Topaz are unbalanced, so i'm guessing its -10 then as well. Is there anything i should be wary about when hooking up a patch bay and will be patching my aux outs to different BALANCED +4 gear that will be terminated in the bay as well?

Besides a lower signal, is there anything occurring when using -10, unbalanced aux sends with +4 balanced boxes in any regards, not just patchbay issues?

Seriously, a few years ago when i didn't know anything, sometimes it was easier, just plug something in and if it works or sounds good, then you're good. Now with a little knowledge, i'm questioning EVERY SINGLE THING I DO, and regards to patchbays, which are there to make work easier, its taking so much to make sure its done right in the first place so i don't have redo it all over again...AND then work flow is supposed to be easier.. grumble.

[honkyjonk]

Yeah,

No kidding. After you're done w/ that patch bay, just stop right there and don't proceed any further into the DIY world. My God, what a time commitment a couple of the mics I've modded have been. Not to mention this Hammond problem I'm having.

Shoot.

I just want to make music yo!