MP-2 Microphone Preamplifier
User Guide and Technical Information
Page 5
©1999-2000 Sound Devices, LLC
Operational Notes
Input Circuitry
The isolation characteristics of transformers are
superior to other balancing techniques for the
adverse and uncontrolled environments of field
production. Input transformers provide complete
galvanic isolation from the source, meaning there
is no direct electrical connection. Signals are
“transformed” magnetically. The MP-2 features
expensive Lundahl input transformers, which are
unparalleled in sound quality. Lundahl input
transformers use premium magnetic core material
and advanced winding techniques to achieve high
signal handling capability and flat frequency
response while keeping distortion to a minimum.
Because of their inherently high common mode
impedance, transformers are unrivaled by any
other type of input for common-mode noise
rejection.
Output Circuitry and Tape Output
Each line level XLR output of the MP-2 uses a
discrete, six-transistor, “impedance balanced”
output stage. The circuit uses oversized, high
speed transistors to achieve low-distortion, robust
line driving capability. Pin 2 is driven with signal,
and pin 3 is not. [A common misunderstanding is
that a “balanced” output refers to equal and
opposite signals on pins 2 and 3. Correctly,
“balanced” refers to equal
impedances from each
signal (pin 2 and pin 3) to ground,
not the signal
voltage.] To drive unbalanced inputs, pin 3 can be
grounded or left unconnected. There is no change
in signal level driving balanced or unbalanced
inputs.
The Tape Output is designed to feed consumer
level devices, such as computer sound cards, DAT
or MiniDisc recorders, and cassette recorders. A
cable wired with 3.5 mm TRS to 3.5 mm TRS or,
3.5 mm TRS to Left/Right phono (RCA) connectors,
is useful when directly connecting the MP-2 to
portable consumer audio electronics.
Phantom Power
Microphones requiring phantom power should use
the lowest voltage acceptable to maximize MP-2
battery life. Condenser microphones that can
operate on phantom voltages from 11-52 volts will
not have a performance benefit with 48-volt
phantom; therefore 15-volt phantom is
appropriate. The 15-volt setting will increase
battery life versus the 48-volt setting.
Microphones requiring 48-volt phantom will not
operate, or may operate with lower headroom and
increased distortion at the 15-volt setting;
therefore use 48-volt phantom for these mics.
Consult your microphone documentation.
Dynamic microphones do not require phantom
power. A properly connected balanced, dynamic
microphone will not be affected by the presence of
phantom power nor will it draw any current.
However, it is good practice to turn phantom
power off when not needed. Poor or incorrectly
wired microphone cable can cause audible artifacts
in microphone signals. Some wireless receivers
outputs are adversely affected by the presence of
phantom power, therefore, consult the wireless
receiver documentation.
High Pass Filter
The two-position high pass (low cut) filter in the
MP-2 is useful for removing excess low frequency
energy in audio signals. This excess energy can be
caused by multiple sources, including wind noise,
vibration, unidirectional proximity effect, or high
ambient noise levels. The 80 Hz position is
appropriate when recording general speech, music,
and ambient sound. The 160 Hz position is useful
to enhance speech clarity. The MP-2 high pass
circuit topology is unique in that the filters are
placed immediately after the input transformer,
before any active gain circuitry. This gives the
MP-2 higher headroom with low frequency signals,
as the low frequency signals are not amplified
before they are removed, as in most other designs.
The high pass filter is a single pole design (slope of
6 dB per octave) and uses high quality film
capacitors for very low distortion. The high pass
filter switch controls both inputs. The center
position of the switch removes the filter from both
audio paths.
When possible, attempt to equalize at the sound
source with microphone selection, use of
windscreens, shock mounts, microphone
placement, and onboard microphone filtering.
Multiple high pass filters (filters on microphones
and on the MP-2) will give an additive effect,
increasing the slope of the filter.
M/S Stereo Matrix
Mid/Side stereo recording is an often used stereo
technique for live music and sound effects
applications. With the implementation of the 5.1
