Topic: Balanced --> unbalanced

[Jamos]

Hey all you cable builders out there...
I want to build a pair of balanced XLR M --> 1/4" TS cables.

Just wondering what's best to do with pin 1 of the XLR?  Some sources say that you should just leave it open on the TS end, and others say that it should be jumpered to pin 3 (ground) at the XLR.

[Jamos]

I've always thought pin 1 should be tied to the shield.  Bigger question is what to do with pin 3 and that depends on the gear involved.

http://www.vandenhul.com/artpap/wiring.htm

Thanks for the link.

Yes, you're right...I had 1 & 3 backwards.

I'll be coming from an Apogee Mini MP.  Apogee claims the outs are "electronically balanced", which I'd probably regard as fig. 1 on the vanderhul page:
http://www.vandenhul.com/artpap/wiring4.htm

Apogee claims:
"On the output side, the Mini-MP uses Apogee’s newly developed electronically balanced line drivers which were designed for the Mini-Dac and simulate true transformer behavior. The result is perfect symmetry when used in balanced mode (even with an unsymmetrical load) and no increased distortion when used unbalanced."

So I think the MP will be fine whether I tie the pin 3 to the shield or not.

[heath]

i almost always tie low to ground.

[ghellquist]

i almost always tie low to ground.

My two cents on this. I am no expert, but I´ve dabbled in electronics for 30 odd years and has done my share of mistakes.

Now, depending on circumstances that can be a bad idea, or a requirement. The situation is as follows.

1 - the output has two amplifiers.
One sends the "hot" pin 2 signal, another the "cold" pin 3. If you connect the output of pin 3 to ground, you are putting the output of the "cold" amplifier directly to ground. It will most probably not be destroyed (see, I said most probably), but it will draw a lot of unnecessary current. A bit of heat and a bit of extra drain on any battery may be the effect.
2 - the output has a transformer.
Now, in budget and modern equipment we seldom see transformers on the outputs. They are quite frequent in field mixers used for film or TV work though and in vintage equipment they are quite common.
The transformer output is electrically isolated from everything else. Therefore you have to connect both ends of the wiring, meaning that to get any useful signal you have to connect "cold" pin 3 to ground.

There is a multitude of configurations out there, where the manufacturer knows that people are going to connect pin 3 to ground (regardless what the manual may say). These generally are sort of "pseudo"-balanced inside the box. The mini-MP is one of them. My guess is that it is better to leave "cold" pin 3 unconnected for those as well, but it surely depends on the exact circuits.

Gunnar

[heath]

great input.  as i deal primarily in vintage studio gear, option 2 applies to me, hence my tying low to ground

[Nick's Picks]

why would you wire it any differently than standard balanced?

pin1 > shield
pin2 > tip
pin3 > ring


or am I reading something wrong?
going from MMP > ?

any way..
I always ground 3 into 1...
but wonder what happens if you just leave 3 disconnected.  the signal never leaves the preamp at that point...well, to the pin of the XLR any way.