Studio Technologies Mic-Pre - Manual (Page 13)

Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 15
4) Connect Mic-PreEminence balanced
line output to scope: pin 1 to scope
common, pin 2 to scope input channel
1, pin 3 to scope input channel 2. In this
way the two traces will show both sides
of the balanced line output.
5) On scope: both input channels set for
AC, sensitivity to 5 millivolt scale.
6) On Mic-PreEminence: set the two CMR
trim pots of the channel under test to
12-o’clock (when looking from the front
of the unit).
7) While watching both traces on scope:
in tandem, adjust the trim pots slowly
clockwise to give minimum but equal
levels for both traces.
8) On scope: adjust input sensitivity to
0.5V scale.
9) Change 1710A generator output
connection to Mic-PreEminence mic
input: one terminal of balanced output
to pin 2, the other balanced output
terminal to pin 3, CT terminal to pin 1.
This puts a differential mode signal on
the Mic-PreEminence input.
10) On scope: observe both traces. The
two AC voltage levels should be equal
within
±
20 percent of each other. This
step confirms that the output is bal-
anced. If not go back to step 3 and
again perform the CMR adjustment.
11) Connect the 1710A generator output
to the Mic-PreEminence mic input in
the differential mode configuration as
previously described in step 9.
12) Connect the Mic-PreEminence
balanced line output to the 1710A
analyzer input (balanced): pin 2 to one
side of balanced input, pin 3 to the
other side.
13) On 1710A: analyzer mode to set level,
set adjust pot to get 0 reading on meter.
14) Connect the 1710A generator output to
the Mic-PreEminence mic input in the
CMR mode configuration as previously
described in step 3.
15) On 1710A: mode switch to dB volts, it
should measure –64dB minimum. (The
–64dB reading relates to an actual CMR
measurement of 70dB when the test
setup is taken into account.) After
measurement is taken, change mode
switch back to set level.
16) If CMR measurement is not –64dB or
better (e.g., –70dB, –80dB, etc.), go
back and start CMR adjustment proce-
dure again.
17) If any repairs have been performed
on the other channel, repeat the entire
procedure for that channel.