American DJ Mix 44 - Manual (Page 2)

THEORY OF OPERATION
The Mix 44 combines four separate mixers into one unit, pro­
viding a versatile method of line level audio signal mixing and
distribution. The four input by four output matrix design allows
flexible routing of four input signals to as many as four sepa­
rate locations at the same time. A typical use for the Mix 44 is
as an outboard four channel matrix with four buss audio con­
soles, to provide multiple feeds. All inputs and outputs are
active, electronically balanced circuits accessed through XLR
connectors. The input section and all critical gain sections of
the Mix 44 use the same IC chips as top professional mixing
boards. The inputs are instrumentation grade differential
amplifiers which yield exceptionally high Common Mode
Rejection (CMR). The C.M.R. of the Mix 44 is greater than
75dB, 20 to 20KHz. The Mix 44 has a 1 Meg Q. input imped­
ance allowing it to tap onto any balanced audio line without
loading it.
adequately "turn off line level signals. Maximum signal level
through the Mix 44 at clipping is -t28dBm balanced and
-i-22dBm unbalanced. The same figures apply to both the input
and the output and individual clip LEDs are provided which
illuminate at -3dB below actual clipping. With THD+n typical­
ly less than .02% in the entire audio spectrum and a unity gain
signal tp noise ratio greater than 85dB with 22dB of headroom,
the Mix 44 delivers excellent sonic performance. An internal
provision has been made for a direct input to the sum buss of
each mixer. The Mix 44 can be individually customized to take
advantage of this feature if required.
The male output XLR connectors on the Mix 44 are actively
balanced with pin 2 being positive, pin 3 being negative and
pin 1 being audio ground. For unbalanced operation use pins 1
and 2 leaving pin 3 UNCONNECTED.
Each of the 4 inputs is connected through a female XLR and is
parallelled to a male XLR thru jack for normal operation. Pin 2
is positive, pin 3 is negative and pin 1 is audio ground for all
connections. Next to each male XLR there is an input select
switch which determines how matrix 3 and matrix 4 are fed
input signal. With the channel input select switch set to the
normal, loop thru "in" position, the female and male XLR are
parallel wired for in and thru connections. With the channel
input select switch in the "out" position, the female XLR
becomes the input for matrix 1 and matrix 2 only and the male
XLR becomes the input for matrix 3 and matrix 4. This config­
uration eliminates the thru connection but increases flexibility
by completely separating mixers 1 and 2 from mixers 3 and 4.
Female to female XLR adaptors can be used to change the sex
of the male connectors.
All the gain controls on the Mix 44 (Channel gain and Master)
have a range of -60 to +13dBm. Total gain of the unit is 26dB.
With both the channel and master volume controls at the same
position, unity gain is at the 12 O'clock knob position. The
60dB of attenuation in the off position allows the Mix 44 to
The Mix 44 has a monitoring section consisting of channel
select switches, an LED VU meter, a headphone volume con­
trol, and a 1/4" TRS headphone jack. Selecting any combina­
tion of the 4 channel select switches routes those channels'
audio signals to the headphone circuit and the LED VU meter,
allowing the user to monitor the output of the mixers. The VU
LEDs display, in dBm, the exact level that is at the XLR output.
The headphone circuit is a mono type which drives both left
and right stereo earpeices. The circuit works with any head­
phones of greater than 20 ohm impedance. The headphone vol­
ume control also has a gain range of -60 to +13 dB to accom­
modate a wide range of audio levels.
The Mix 44 utilizes two dual primary power transformers which
can be configured with internal jumpers for 120 VAC 60Hz. or
230 VAC 50Hz. operation. There is an internal fuse on the hot
side of the AC cord, and the power switch makes and breaks
both the hot and neutral legs of the AC cord. A ground lift
switch is provided which can disconnect the audio circuit
ground from the AC chassis ground.