From djacques@csulb.edu Tue Jun 05 08:32:46 2001
Subject:RE: mic wiring

I too question the use of two mikes on a Pro3T... I had one mike internally
wired to an XLR and it was quite adequate. In addition, I found that the
live output from the horn serves as the extra sound point, making the option
of a second mike moot...

You will also find that if you do not insulate the microphone correctly, you
will pick up a TON of noise from the Pro3 motor. Two mikes will multiply
this effect. In addition, you need to isolate the microphone far from the
transformer. Where would that second mike be located?

-----Original Message-----
From: SimpsonDan@aol.com [mailto:SimpsonDan@aol.com]
Sent: Tuesday, June 05, 2001 8:10 AM
To: CloneWheel@yahoogroups.com
Subject: Re: [CWSG] mic wiring

I'm wiring up the 2 mics I got from from Mouser to a female XLR for the
Pro3T.>

No such thing as a stupid question, Dean, and this one is actually pretty
complicated.

I'm sure there are others on this board with more electronics experience who
can provide a better explanation (Bruce, for sure), but I'll take a first
shot.

An XLR is a three-pin connector: Pin 1 (on the upper right on the female
connector, the upper left on the male connector) is the ground. Pin 2 (the
other side) is the hot signal (at least in new gear) and pin 3 (at the
bottom) is the cold. Most mics, though not all, are balanced, which means
that Pin 2 contains the hot signal and pin 3 contains a phase-inverted copy
of the same signal. The benefits are a 3dB increase in overall gain and
what is called common mode rejection. Any noise that enters the cable gets
canceled at the input since the phase relationships of the two signals are
opposite.

It is a bad idea to try to wire two mics to a single XLR. Bruce and others
can probably provide the technical rational, which is going to involve
impedance problems, among others, but I can tell you that it is not going to
work. A Y cable is not going to make it any better.

If you have two mics you have to connect them to 2 separate XLRs and then
use the mixer to combine the signals. If you only have one inpuit on the
board, then you are *FAR* better off with a single mic than trying to rig up
anything with two mics into a single XLR.

Bruce, can you add (or subtract) to this cryptic explanation? You are the
expert in the physics of this stuff.

Dan

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