[sdiy] Request brain dump on balanced lines

[media.nai at rcn.com]

At 3:09 PM -0500 10/11/02, Grant Richter wrote:
>
>Can someone familiar with balanced mixing console lines summarize the
>information?
>
>What I need to know is typical voltage levels and impedance's for TRS jacks
>and XLR connectors.

In the real world, there are no typical levels and impedances :)

Mic inputs can range from less than 100 Ohms or more than 4K, but 2K is
typical for your average board.

There are line inputs out there that are less than 10K, but thankfully,
they are usually between 10-50K.  Most specs simply list them as ">10K".

10Vp-p is about 20dBu into 600 Ohms, which might be too hot for some mic
pre's.  However, most boards have pads, line level inputs, or both.

There are AD units that use the same TRS jacks for mic and line.

>I'm trying to figure out a nice (i.e. cheap) way to interface +/- 5 volt
>single ended synth signals to your typical mixing console balanced inputs.

The least expensive, and least confusing, is to wire it to a TS plug,
ground to shield, hot to tip.  That says "unbalanced line signal" to any
soundman that might find it dangling.  It will work fine with a TRS jack --
nothing special is needed.

>Is a single ended to balanced transformer a good way to go, or is an active
>differential output better?

I would say for short runs at line level, the best way would be to wire it
directly.  Unless this is for a very hostile environment, adding
transformers or another amp stage will add more noise than balancing will
prevent, nevermind the distortion.

If you need a long run, just use a small mixer (like a Mackie 1202) to
balance the signal.