To the left of the Lamps switch is the
Output Limiter (LIM)
three-position switch. The
setting of this switch (Off, “S” separate, or “G” ganged) determines the limiting function.
Two independent and separate limiters are built into the AlphaMix; particularly useful
when recording split tracks. This allows one limiter to engage when the limit threshold
(+3 on the meter) is reached. If the other channel remains below threshold it will not
engage. The compression ratio of the limiter is approximately 2.7 to 1 with a 1mS
attack time and 100mS release. The presence of output limiting is displayed on the
meter. PSC recommends use of the limiters at all times when recording to Betacam
type cameras.
The last switch on the lower left of the front panel is the
Power (PWR)
switch. This two-
position switch selects the power source. The AlphaMix can be
powered from an internal battery (IN) or an external source (EXT).
Headphone output
function controls are located on the upper
right corner directly above the LIM switch. These controls consist
of a recessing output volume (HP VOLUME) pot, a source toggle
switch (HP) and a rotary mix select switch. The headphone
circuitry of the AlphaMix will drive most any headphone with
impedance of 32 to 600 Ohms.
After setting the desired headphone level, the rotary
HP VOLUME
pot can be recessed
to prevent accidental changes. To the right of the volume pot is the three-position
source toggle switch
(labeled
HP
). This switch enables the operator to monitor the
AlphaMix’s tape returns. Tape returns arrive through the Hirose™ 10-pin connectors on
the Output Panel. In the center “D” position the operator is able to monitor the mixer
directly. Positions “A” and “B” monitor camera/recorder returns. “A” and “B” levels can
be adjusted to match the signal levels of most any device using a small jeweler’s
screwdriver. Levels are adjusted on the bottom panel. Below the HP VOLUME pot is
the
mix selector
(not labeled). This 5-position rotary switch determines the monitoring
of Left only (L), Stereo L/R (S), Right only (R), mono (M) or Mid Side Stereo (MS).
When
recording stereo X-Y or M-S signal
s the headphone mix selector should be set
in the Stereo or MS position respectively. Additionally, the input-ganging switch located
on the bottom of the mixer must be set to the “ganged” position. This allows the inputs
of channels 3 and 4 to be ganged enabling both channels to be controlled by pot 4.
With either type of stereo mixing, the pan pots for channels 3 and 4 remain independent
and should be panned hard L (3) and R (4). When recording X-Y stereo; identical
microphones are plugged into channels 3 and 4. M-S stereo recording requires that the
middle “M” microphone (cardioid) is plugged into channel 3 and the “S” side microphone
(bi-directional) be plugged into channel 4. The headphone amplifiers receive MS
decoded signals that appear as standard stereo audio for monitoring without affecting
the main XLR outputs.
