MP-2 Microphone Preamplifier
User Guide and Technical Information
Page 6
©1999-2000 Sound Devices, LLC
audio specification for DTV, M/S stereo is often
used to capture stereo ambience.
The
HP ONLY position routes M/S decoded signal
to the headphones, while sending unaffected Mid
and Side signals to the outputs. This allows the
flexibility of decoding later in post production while
monitoring in stereo to optimize microphone
placement. The
HP + OUTS position can be used
to decode directly to the Line Outputs, Tape Out,
and Phones for decoding on location. The width of
the stereo image can be varied by changing the
gain of the Side (Input 2) signal relative to the Mid
(Input 1) signal. More side signal relative to the
mid signal widens the stereo image. Mono
compatibility is maintained with M/S stereo.
Headphone Monitoring and Tape Return
Headphone monitoring is an essential need in
production audio. The MP-2 enables monitoring of
program (mixer) audio or a second audio source.
In normal operation the headphones monitor the
output bus directly. Using the Tape Return input, a
second audio source can be monitored in the
headphones. This is useful to verify that signal is
reaching cameras and tape machines. The three
position Tape Return switch on the front panel
selects the audio source being monitored. The left
and right positions monitor the tape return audio.
Left is locking, and right is momentary. The center
position monitors the Left and Right outputs of the
MP-2. As the MP-2 can drive headphones to very
high levels, care should be exercised when
monitoring.
Limiters
The MP-2 has two built-in peak responding limiters,
one for each input channel. The three-position
LIMITER switch on the input panel activates both
channels limiters. Each limiter in the MP-2 is a two-
stage circuit; the first stage keeps the input gain
stage from clipping; the second stage limits the
variable gain stage to the level set by the Limiter
Threshold control. This unique two stage topology
limits the gain stage directly after the mic input
transformer, to make the front end virtually
“unclippable”, but does not change the input
impedance as other “at the mic” limiters do. The
circuit enables the MP-2 to limit, when necessary,
in excess of 50 dB, making it very difficult to clip
the unit no matter the gain setting.
The three-position Limiter switch can be set to
operate in either dual mono or stereo linked
operation. Dual mono operation (ON switch
position) allows each input to limit independently,
responding only to its input signal. Stereo linked
operation (LINK switch position) connects both
limiters, ensuring that the limiters control both
channels identically. This linking is important for
stereo operation to maintain a proper stereo
image. When the limiters activate, the Peak/Limiter
LED on the front panel illuminates amber in
proportion to the amount of limiting for each
channel.
Metering
Above each input gain control is a two-color LED
that illuminates red when the input approaches
clipping (3 dB before clipping). This clip circuit
monitors both the front end gain stage and the
variable gain stage. If the audio signal clips
anywhere, this LED will show it. Above the
headphone level control, the headphone clip LED
shows when either channel of the headphone
circuit is nearing clipping level. The headphone clip
LED also shows when either channel of the tape
return audio is nearing clipping level. Between
these three clip indicators, any clipping, anywhere
in the mixer will be seen before it is heard.
When the limiter is activated, the input LED’s
illuminate amber in proportion to limiting action.
The MP-2 has a highly visible, seven segment LED
output meter. The meter is peak responding,
showing the instantaneous output level in dBu.
Peak readings are essential when the outputs feed
digital devices. The meter uses expensive Gallium
Nitride (GaN) LED’s which allow for excellent
viewing (with minimal current draw) under all
lighting conditions, including direct sunlight. The
front panel Meter Brightness switch controls the
meter brightness (low, normal, or super-bright).
The meter indicates a signal range of 46 dB. From
left to right the first three LED’s are separated by
15 dB and the next four LED’s are separated by 4
dB. This calibration provides a large dynamic range
with good resolution in the critical signal level
range.
Power Sources
The MP-2 is designed to operate from two internal
AA alkaline cells for approximately 6 hours with
typical signal levels (without phantom power).
External DC sources such as AC to DC transformers
and external battery supplies can also power the
MP-2. Because of its regulated power supply
