Patch bay cabling, seeking unbalanced advise

I need to put together some cabling for a soundcraft board I picked up, I'm hoping to use up some materials I have on hand.  The inserts on the console are the standard trs break jack to un-balanced TS.  My patch bays are located in a small rack/shelf above the console, I've got the insert points wired to one patch bay.  It seems obvious that I'd want a second patchbay below that with all the ins and outs of my outboard gear. 

Since the signal is already unbalanced on the console inserts, is there any point in using balanced cabling to connect the back of the second patchbay to the rack of outboard gear?  I ask because I have a few 8 ch unbalanced snakes that came with the console, so if I can I'd rather re-use those. 

Thanks!

maybe..
wont matter with some gear, transformers etc but..

if you are connecting an electronically balanced piece of gear to the unbalanced return you will be better off with pin 3 floating on the output.

if you are wired into a trs patchbay with standard Y cable (trs - ts) then the inverted output will be put to ground and you will stress the output

Thanks
Meaning just leave pin 3 unconnected (at the output of the rackgear) rather than letting it short to ground in the patchbay?

This is how I'm wiring my insert cables...

If you are going to roll your own, I would consider TRS insert to two TRS jacks for send and return. Also use two separate, three conductor with shield cables, one for each TRS destination.

At console insert end connect all shields and all sleeves to console TRS sleeve. Connect both send and return "rings" to console insert Sleeve. Connect console insert tip to one destination TRS tip, and console insert ring, to the other TRS tip. Do not connect shield to sleeve at send/return ends.

Which is the send and which is the return will depend on particular console insert wiring.

Note: if appropriate consider XLR instead of TRS for Send and return terminus.

While this insert is not balanced, using differential wiring can gain you some benefit when interfacing with balanced/differential circuitry in external gear.

JR
__________________
John Roberts
www.CircularScience.com

Click to expand...

yes, you got it.

good advice.

substitute said:

If you are going to roll your own, I would consider TRS insert to two TRS jacks for send and return. Also use two separate, three conductor with shield cables, one for each TRS destination.

At console insert end connect all shields and all sleeves to console TRS sleeve. Connect both send and return "rings" to console insert Sleeve. Connect console insert tip to one destination TRS tip, and console insert ring, to the other TRS tip. Do not connect shield to sleeve at send/return ends.

Which is the send and which is the return will depend on particular console insert wiring.

Note: if appropriate consider XLR instead of TRS for Send and return terminus.

While this insert is not balanced, using differential wiring can gain you some benefit when interfacing with balanced/differential circuitry in external gear.

John Roberts
www.CircularScience.com

Click to expand...

Du.uuh!  Could one of yus initiated please draw a lil' diagram of the above for those of us hu kunt reed en rite.  This is a serious request.

rane notes 110 is all you need.

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

Yeah, that's a great resource!

I started messing with the "John Roberts" wiring last night,  man that is a ton of crap to cram into a 1/4 jack. 

Ricardo, the idea is you have two cables going into one TRS jack, each cable has a 3 wires (tip, ring, sleeve) AND a shield wire.  Everything but the tips, or hot, or + wires gets grounded inside the TRS that plugs into the console.  On the other ends the everything is connected normal, but  you leave out the shield wire...

I think.

last time I made insert cables for mackie and other mixers that use this set up I did the following.  I used 2 pair snake cable. This makes it easy to cram all of that into your 1/4 ends. I prefer the neutrik 1/4 as you have a little more room to cram.  On the  trs ends that connects into the patchbay or into the gear your inserting I wired it as normal Tip ring sleeve. On the trs insert send/return in the console, I leave out/lifted the sleeves, took one channel and wired tip to tip and ring to sleeve. on the other connection take tip and wire it to ring and sleeve to ground.  I found this to work best. Now depending on your mixer one of those is send and one is return.

I think I got a bit lost there, I had to read that about 5 times for it to make sense pucho.
I guess it IS easier with pictures. Show us your Ms PAINT Skills!
still not sure why you would use 2 pairs of snake!!?
also not sure what you're all on about in regard it 'fitting it all in' ???
its just two leads with their shields. (even rca pair girth!) right?

i'd lift the ground at the split ends if needed, not at mixer just on the return usually.
having a couple of patch cables with shield connected only one side would work well too.


so JR/Pucho
both of you's suggest... with your cables wired like that, grounding the rings.
with an equipment chassis (let assume gssl output as an example.)
inverted audio ground reference at output being 0v and an electronically balanced output feeding the 'ring' (pin 3) of your wiring goes straight to 0v via mixers insert gnd.

i can see how it would work for an input comparator (or cross coupled output) but i dont understand in the case of gssl balanced out? or similar may have even less than the 100r  on the outs.

anyway, here is an Excellent drawing, it took me a few hours so i hope you enjoy it

you have my wiring wrong all wrong.

For starters,

2 pair snake cable also known as 2 channel audio snake.

Mogami part number 2930 or whatever cable of your choice.
use this as regular balanced mic/line cable has too thick a jacket and you would not be able to fit both send and return into the 1/4 trs end that is going into the mackie or whatever mixer.

1. the shields are only connected on the end that connects into the gear or patch points for the send and returns.

2. The hot of send or return goes to tip(pin 2) of the insert connector on the console. Now depending on mixer that may be send or return.

3. the hot on the other connector goes to ring(pin 3) of the insert connector on the console. Again  depending on mixer that may be send or return.

4. The rings on both connectors go to ground(pin one) of the  insert connector on the console.

Drawing attached

WRONG... ALL WRONG. lol
sorry Pucho. i thought it seemed strange. glad you clarified.

never heard of 2 pair equaling 2 before, must be some crazy mogami thing.
otherwise, i got it.
anyway i see your big picture now that clears up what you were trying to say.


although if you can help me understand. my question still stands regarding your wiring, you still have the send and returns 'rings' pin 3 wired to ground at the mixer.
I understand shield is only tied one end, from the patchbay (thats fine, I do guitar leads like this with mic cable.)
but, one side of your balanced out is still trying to drive to ground in this configuration... right?

kepeb said:

WRONG... ALL WRONG. lol
sorry Pucho. i thought it seemed strange. glad you clarified.

never heard of 2 pair equaling 2 before, must be some crazy mogami thing.
otherwise, i got it.
anyway i see your big picture now that clears up what you were trying to say.


although if you can help me understand. my question still stands regarding your wiring, you still have the send and returns 'rings' pin 3 wired to ground at the mixer.
I understand shield is only tied one end, from the patchbay (thats fine, I do guitar leads like this with mic cable.)
but, one side of your balanced out is still trying to drive to ground in this configuration... right?

Click to expand...

yes mogami often refers to their multi channel audio snakes as pairs, for example 8 pair is really 8 mic/line channels, 24 pair is 24 channels and so forth and so forth.


Yes but that is because the insert i/o in the mixer is unblanced.

yea,  it's 2 x twisted pair or 2 'balanced channels' .  obviously they're unbalanced inserts as my first drawing indicates and the OP said. what you have drawn is fine for transformer out, 'impedance matched' or cross coupled

I'm definitely NO expert. but all documentation I have seen suggests that your wiring would burn some balanced outs. you NEED pin 3 floating for ic balanced signal feeding unbalanced input.
NOT tied to ground. says this in the Rane notes you posted above.
seems convincing enough to me but i must have misunderstood.

so you're actually supposed to ground unused ic outputs?

kepeb said:

I'm definitely NO expert. but all documentation I have seen suggests that your wiring would burn some balanced outs. you NEED pin 3 floating for ic balanced signal feeding unbalanced input.
NOT tied to ground. says this in the Rane notes you posted above.
seems convincing enough to me but i must have misunderstood.

so you're actually supposed to ground unused ic outputs?

Click to expand...

Indeed, there are problems when intermixing "brain dead" "balanced" outputs with balanced inputs, particularly if a patchbay is involved.

Example.  The widely used Avid/Digidesign 192HD A/D D/A units have  "brain dead"  "balanced" outputs.  You are NOT supposed to ground the "cold" output lines, but instead use only the "hot" and "ground" lines from the DB-25 when feeding an unbalanced destination.  But, this reduces the 192HD output levels (and headroom) by 6 dB.  This is a......ahhhhh....questionable design, but Avid has made million$$$ selling this.

There is really no way I can think of to correct this in a patchbay besides having TWO jacks in the bay for every output from the "brain dead" devices:  1 jack to be used when feeding into a balanced destination and 1 jack to be used when feeding a balanced destination.

The other solution is to add balancing circuitry/transformers at the inputs or outputs of the equipment.  I ran into this situation in a studio (which had 192HD units) when attempting to patch into certain unbalanced input API modules in the studio's lunchboxes.  The least expensive option was to build an external box containing six transformers which connected to the various channels on the lunchboxes which held unbalanced input modules.  (The other option was to add 32 transformers to the outputs of the 192HD.)

Bri

Brian Roth said:

There is really no way I can think of to correct this in a patchbay besides having TWO jacks in the bay for every output from the "brain dead" devices:  1 jack to be used when feeding into a balanced destination and 1 jack to be used when feeding a balanced destination.

Click to expand...

this is an excellent work around!, worth the extra patch slots.

i only have a few unbalanced ins but including tape machine, desk insert returns and some old effects units
that's already over 30 transformers just for the comfort of knowing you're doing it right.
or just continue to fanny around with leads EVERY time you make a patch
it's an overlooked area when setting up permanent connections like that

anyone have experience with 'possible' problems when feeding a differential balanced IN with pin 3 (inverted) floating?

One way round the active balanced output problem is to use a buildout resistor on the leg that can get grounded. At least this way you don't short the output to ground, and you ensure continuity when patching to a transformer in. If you are patching to bridging inputs this will work fine.
Simply put a resistor say 600 to 1K in series with the leg that will be earthed before the jack.
With differential inputs, you must feed both legs or you lose the cancellation that the diff in provides.

if adding the series resistor, then both hot and cold lines will require the same matched resistors to avoid screwing up the CMRR of a balanced/diff input.

Bri

this is true, the resistanc (impedance) needs close matched resistors
this is what i was referring to with the phrase 'impedance matched'(not 'correct' term i know).. cheating
if you're getting out the soldering iron, may as well just do it properly if its not just a patch cable solution.

anyway.
I KNOW grounded outs have been burned but was
looking for someones BAD experience with pin 3 floating on the input.
there is still a reference for the floating pin most times

kepeb said:

this is true, the resistanc (impedance) needs close matched resistors
this is what i was referring to with the phrase 'impedance matched'(not 'correct' term i know).. cheating
if you're getting out the soldering iron, may as well just do it properly if its not just a patch cable solution.

anyway.
I KNOW grounded outs have been burned but was
looking for someones BAD experience with pin 3 floating on the input.
there is still a reference for the floating pin most times

Click to expand...

The pair of matched series resistances is a bit of a kludge and can introduce other problems.  For instance, if you install 602 ohm resistors in series with both the hot and cold leads, and then patch into an input with a 600 ohm input impedance (such as a LA-2 or 1176....vintage or re-issue), then you have inserted a 9.5 dB pad between the source and the input of the 600 ohm device.

I don't understand the second part of the question regarding "pin 3 floating on the input".  If the input uses a transformer, you can NOT float the "cold"/pin 3 line.  What happens with other types of inputs will vary if you let the cold input line float.

Bri