#2194 - 08/06/01 12:38 AM
Is there any benefit in using a balanced cable in an unbalanced connection?
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Wiggum
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Registered: 01/28/01
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Hey all,
This sounds like a dumb question, but is there any benefit in using a balanced TRS cable in an unbalanced connection?
I thought I read that with a certain configuration, you could gain some shielding, or perhaps some other benefit.
Thanks,
Wiggum
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#2195 - 08/06/01 10:59 AM
Re: Is there any benefit in using a balanced cable in an unbalanced connection?
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fantasticsound
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In my limited electronic knowledge, no, a TRS cable will provide no benefit in an unbalanced circuit.
However, you may be mistaking TRS balanced for another concept. There is a method of wiring, involving a 2 conductor + shield cable, used with TS connectors that is supposed to provide superior shielding. I've heard it referred to as "mushroom" wiring the cable. It's very simple to do.
Mark one TS connector to differentiate the two ends of the cable. I sometimes use angle jacks for the output from my guitar and a straight plug for input to the 1st pedal/preamp/guitar amp/etc.
[*]Solder the + conductor to tip at both ends of the cable.
[*]At the output end, trim back the shield and, if necessary, insulate it with some electrical tape. Solder the - conductor, only, to the sleeve.
[*]At the input end, solder both - & shield to the sleeve.
That's all. Someone explained to me the reason this shields your signal more effectively, from noise, in an unbalanced connection. Unfortunately, this information has slipped away from me.   
If someone else would be kind enough to enlighten us, I, too, would be most appreciative.
------------------
Neil
Reality: A few moments of lucidity surrounded by insanity.
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#2196 - 08/06/01 12:16 PM
Re: Is there any benefit in using a balanced cable in an unbalanced connection?
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miroslav
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***See my next post below, I've left this one intact since much of it is relevant AND usefull for BALANCED connections.***
Yes...that's the ticket. Using a 2 conductor and lifting the shield at one end. I am in the process right now of making (4) 26 channel snakes using that method for all the single conductor plugs.
Each channel of the snake is 2 conductor + mesh shield w/bare 3rd wire cable.
One end:
+ tip (first conductor)
- sleeve (both second conductor AND mesh shield)
Other end:
+ tip (first conductor)
- sleeve (JUST the second conductor)
As fantasticsound pointed out...this is the tricky part...how to keep the mesh shield from touching the sleeve. Simple solution...place shrink wrap tubing over several inches of the cable end. Expose ONLY the two conductors (about 3/4 inch), cut back the shield so that the shrink wrap will completely cover it, leaving only the two conductors. Now you can place the plug around the cable and have only the 2 conductors touching the tip/sleeve respectively (the shield is under the shrink tubing).
As I said above...I'm using this soldering method and it actually works quite well...now comes the big moment of truth...will it effectively keep noise out???
Here's the rub, by disconnecting the shield at one end you can effectively remove ground loop hum but you also stand the chance of introducing RF interference because all those disconnected shields have now become "antennas". Well...you have to try it and see.
I've left myself the option of easily attaching the shields if needed by NOT completely cutting away the little wire that makes contact with the shield. With better quality 2 conductor cable you get that bare 3rd wire that is really part of the shield, and by only cutting back the mesh and NOT this wire, I've then taken this 3rd wire and just tucked it's 3/4 " length UNDER the shrink wrap. So...if I need it I can just pop it out from the wrap and solder it on without having to first unsolder the previous connections (very slick If I may say so myself )
I've read one way to reduce the chance of your shield acting like an antenna is to attach a 0.1 - 0.01 micro Farad ceramic capacitor from the floated shield end to the chassis...but now you are back to a potential ground loop hum problem. Haven't tried this yet though...it's not hard to do or a major cost to attach the caps, but I just get sick of all this soldering.
Last thing...which end of the cable do you float? General practice is...either, as long as you stay with the same scheme throughout your set-up. I am currently going with the outputs connected and inputs disconnected...that is...at my mixer, where the signal is LEAVING (output) I have the shield connected, and where it coming IN (input), I float the shield. This follows for all the gear you have and don't get criss-crossed when/if you use patch bays…stay with the scheme. You could also go the other way INPUTS connected and OUTPUTS disconnected, but pick one and just stay with it through out.
Don't get too crazy theorizing though...just connect some stuff one way and see what you got...if there is no hum or RF interference...LEAVE IT ALONE...regardless of how the wire is connected. If you do come up with any problems...treat JUST the problem connections first...then if needed....work you way deeper through the rest of your gear. Often it could be just one bad connection causing a LOT of problems and the rest are fine.
GOOD LUCK!
This message has been edited by miroslav on 08-06-2001 at 01:10 PM
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miroslav - miroslavmusic.com"Just because it happened to you, it doesn't mean it's important."
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#2197 - 08/06/01 02:55 PM
Re: Is there any benefit in using a balanced cable in an unbalanced connection?
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miroslav
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OK...after doing some more research and talking to the techs at Rane (great people, thanks Chris!)...I'm going to re-evalute my own situtation and my post above.
Apparently, lifting the shield at one end of an unbalanced cable like what we are talking about above, is NOT going to really solve anything and WILL possibly bring RF problems into the picture.
The recommandation for 2 conductor + sheild for unbalanced, single-ended plugs/jacks:
+ tip: (first conductor)
- sleeve: (second conductor AND shield connected AT BOTH ENDS OF CABLE)
NO FLOATED SHEILDS...that only helps BALANCED connections.
OK...so now I have to correct some of the cables I was making yesterday...SHIT...well, good thing I left the shield wire under the shrink wrap...should only take about a 1/2 hours to correct 16 channels worth.
Check out the Rane web site...Tech Note 110 is required reading for anyone doing system wiring...though it gets a bit spooky when you're mixing unbalanced/balanced connections...trial and error
This message has been edited by miroslav on 08-06-2001 at 01:11 PM
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miroslav - miroslavmusic.com"Just because it happened to you, it doesn't mean it's important."
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#2198 - 08/07/01 01:53 AM
Re: Is there any benefit in using a balanced cable in an unbalanced connection?
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Wiggum
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Registered: 01/28/01
Posts: 428
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Sounds too complicated for me...
But I do appreciate the info. Realistically, at the lengths I am using, I don't see much opportunity for interference. With some high quality unbalanced cables, I think I'll be fine.
Thanks,
Wiggum
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