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Subject: [motm] Re: How to connect balanced signals to the MOTM

From: Mark <yahoogroups@...>
Date: 2006-03-31

On 3/30/06, ivancu2 put forth:
>As mentioned, MOTM outputs are unbalanced and substantially higher
>than normal "pro" line-level outputs.

No, they aren't.

On 3/30/06, Paul Schreiber put forth:
>MOTM uses very large signals on the outputs: 10V pk-pk which is something like
>+24dBu
>
>Most "studio" gear uses +4 dBu which I think is like 1.5V pk-pk.

Actually, most studio gear is more or less 22V pk-pk, which is 20dBu.
Admittedly, the designation "+4 dBu" is a bit misleading. MOTM is
10V pk-pk which is around 13dBu. Which isn't as significant a
difference as one might think. MOTM is quite compatible with most
line-level gear.

The only exception might be the MOTM-120. I don't have one myself,
but I have read numerous complaints over the years that it isn't hot
enough.

>Mics need balanced cables because their outputs are in ∗microvolts∗ to say 5mv
>(that's 0.005V).
>
>Since the 'driving' signal is so small, any hum or noise is ∗relatively
>significant∗.

This is true. Imho, the advantage of using balanced interconnects
for line level over the typically short distances in most studios
isn't the common mode rejection, but that its consistent
implementation prevents ground loops and provides better level
matching.

On 3/29/06, Charles Stella put forth:
>The proper way to unbalance a balanced line is not to drop ground
>but to tie Pin 3 (XLR) or the Ring (TRS) to ground.

Which is what generally happens when one uses a TS cable with
balanced TRS jacks, however there are instances (eg. you are using a
one-conductor cable with equipment with mismatched grounds) where it
is preferable to float the ring even though it causes a 6dB loss in
signal. The ideal solution in going from TRS to TS would be to use a
2-conductor cable where the signal ground (the ring) is connected to
the the sleeve of the TS, and the TRS sleeve is connected to the cable
shield but is left unconnected at the TS end. Although that usually
isn't necessary.

>When you plug a balanced TRS cable into your MOTM the Ring connector
>is automatically grounded so there's no need to make a special cable.

I do not think that is true. Although, with good equipment the
sleeve is still grounded (to the chassis) at both ends so it should
still work, even though it is not the best way since you are ignoring
the signal ground.

However, be warned, there is equipment out there with floating
unbalanced TRS jacks where the sleeve is not connected. While these
sort of bullshit balanced connectors will work if you use a TRS cable
to connect to a TRS jack that does have its ring and sleeve
connected, and will also work if you use a TS cable, they will not
work properly if you use a TRS cable to connect to a TS jack such as
MOTM. (Oddly enough, it doesn't seem to occur to the manufacturers
that the shield remains completely unconnected when using TRS cable
to connect these pseudo-balanced TRS connections together!!)

Almost all equipment with TRS jacks is made with the expectation that
someone will stick a regular TS plug into it at some time or another.
So I strongly recommend using regular TS cables to connect MOTM to balanced
TRS, and only trying other options if noise or other problems occur.