Re: When not to ground pin 3
- From: Walt <walt_askier@xxxxxxxxxxxxxx>
- Date: Thu, 22 Jun 2006 12:30:32 -0400
apa wrote:
Walt wrote:
apa wrote:
I have a Tascam MS-16 with balanced outs wired into a patchbay which
mixes some balanced and unbalanced gear. All of the unbalanced
connections are wired nomally at the bay and have the ring shorted to
the sleeve at the connector end. I was getting a lot of bleed from the
MS-16's outputs into the board and into the inputs some of the effects
in the rack. The only solution was to lift pin 3 on the MS-16 outputs.
Is this the proper way to unbalance the MS-16 (or any other piece of
gear with a transformerless output that carries signal on both pin 2
and 3) or is it an indication that I've got something wrong with my
patchbay wiring?
Yes, the best way to connect an active balanced (transformerless) output
to an unbalanced input is to just pick off the non-inverted signal and
throw away the inverted signal. Assuming pin 2 is hot, lift pin 3 and
you're done. A TRS 1/4" does this automagically when inserted into an
unbalanced 1/4" connector.
However, the best place to do this is not at the output of the MS-16 or
at the pacthbay, but at the input of the unbalanced device. Keep the
signal balanced until it reaches the inupt you're driving and lift the
unused signal there. That will obviate the problem you describe below.
It sounds like you have 1/4" connectors feeding the input that tie the
shield and one of the conductors to the sleeve. Snip the conductor and
your crosstalk problem should go away. Or, replace the tip-sleve
connectors with trs. Just be aware that it won't work if you have
transformer balanced outputs.
Ideally I'd like to keep it balanced because I have no polarity reverse
on the board and I can reverse with a patch cable if I need to, but I
can live without that if lifting pin 3 is the only solution.
That's the rub - some of the gear is transformer balanced - so for that
to feed the unbalanced connections properly, I need to keep the ring
grounded. Unless I snip the pin 3 wire on all the unbalanced
connections and use a patch cable that grounds pin 3 when I want to
connect the transformer pieces to the unbalanced inputs.
Ok, I see your dilemma. You are trying to mix three flavors of audio connections (active balanced, transformer balanced, and unbalanced) via a patchbay and want to be able to patch anything into anything else. There are approaches that make any two of the three interoperate, but I am unaware of any scheme that will make all three work together gracefully. The serious professional approach is to make all the inputs electrically identical and all the outputs electrically identical (same level, same polarity, same or at least similar impedences, same pin high, etc.) You can get away with two out of three, but not all three.
Converting all your unbalanced stuff to active balanced is probably not cost effecteve, so maybe getting a couple of RDA stick on modules for your transformer gear to make it look like active balanced to the outside world would help. Good luck.
//Walt
.
- References:
- When not to ground pin 3
- From: apa
- Re: When not to ground pin 3
- From: Walt
- Re: When not to ground pin 3
- From: apa
- When not to ground pin 3
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