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Make
the number
lower
for ohms.
Maximum
load =
minimum
ohms, so read carefully.
When the minimum/maximum
statement is made
you can safely assume that the manufacturer has already
done the "saven times is best" ratio calculation, And the
number
given in ohms
does not have to be multiplied.
You can match
the ohmic value of your input to this
number of ohms successfully, but as always, higher ohms
will be okay (Less load).
7
QUICK TEST FOR SAFE LOADS WITHOUT
USING
TEST
GEAR
tf you don't know the exact value input impedance
for a device you want to connect there are still a couple
of ways to test it.
1, Listen to the main signal output {line out or Aux
out) as you remove and re-connect the device to the
direct out. If you hear a drop in level or a change in
the.tonal balance of the sound on the main line out,
the device is likely to be drawing too much current
and is unsuitable.
lf you can get a steady tone to work with, you can
read your
VU
meter
and
make
this measurement.
Patch the steady tone through the mixer from input
to line out. Set the faders so the tone reads "O" VU
'on the meter.
Now connect the device you wish to
check to the "direct out" on the input module you
are using for the steady tone,
If the drop in level on
the meter is more than 0.5 dB, the device has too low
a value of input impedance.
It will not damage the
mixer to use it, but it will affect the quality of the
signal on the main line.
Nn
If making the connection
to the direct out causes
the main line signal to drop 6dB, the input impedance
of the device is the same as the true output impedance.
You should also know that to make the "disconnect,
re-connect
the load" test in. section 1 above, you must
actually pull out the connection.
Many devices
will affect
a circuit when the signal cable is connected, even if they
are not plugged
in the power line, or their power (AC)
switch is in the off position.
3. THE MODEL 15 FROM MIC IN TO LINE OUTS
In our description of the seven different types of
module
used
in the M-15, we'll disregard the physical
layout and follow the block diagram, or actual wiring
sequence.
3.1 INPUT MODULE
All sixteen input modules are identical and can be
interchanged
without
modification.
An
additional
8
modules
can be added
io the frame at any time. The
extra
positions are completely
wired, with one excep-
tion. The RMX
(remix) position will be inoperative on
the last 8 positions (17-24) because there is no provi-
sion on the tape A or B circuit for the extra 8 busses
necessary. All other features will be identical in the 24
input mode.
MIC
IN XLR
CONNECTOR
This connector and the small amount of wiring
immediately in front of the input transformer are the
oniy parts of the M-15 that use the 3 wire balanced
type of circuit. The Mic in XLR, the pad of 20 dB that
is switch
selectable
and
the transformer
primary
are
"balanced".
All circuits thereafter are 2 wire "single
ended", one hot lead, one ground.
MIC ATT
SWITCH
When
this switch is set to the left, a balanced pad
lowers the "Mic In" level by 20 dB, Since the maxirnum
permissible
input
to the transformer
is 0 dB (1 volt),
when
high output
mic's are used on very loud sounds,
extra external pads may be required to lower the input
signal to safe levels. The input load impedance of the
"Mic In" group of parts is 20 kohms. This circuit cor-
rectly matches 50-250 ohm low impedance microphones.
LINE
IN JACK
An RCA jack on the rear of each input module. The
maximum signal you can apply here is +28 dB (25 volt).
The Mic Att switch does not affect this input. The input
impedance is 50 kohms.
INPUT
SELECT
SWITCH
This switch has 3 positions, left selects the Mic in
XLR, center selects the Line In RCA jack on the back
of the module, and right, marked
"w" (remix), selects
as an input one of the "Tape In" jacks on the buss master
modules.
Since each input module will receive only one
"Tape In" signal, we'll provide a chart to show which
signal goes to which module.
The "Tape In" A and B systems normally feed the
monitor sections on the buss master modules.
The "s#"
{remix}
position
on
the
input
module
will allow you
to route tape playback signa! to the input module for
final mixing
without
moving
the cabies plugged
in at
tape A or B to the input "Line In" jacks, in addition,
selecting this "m" (remix) position on the input module
will not disable the normal
operation of the monitor.
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