MP-1 Microphone Preamplifier
User Guide and Technical Information
Page 4©1999-2000 Sound Devices, LLC
Operational Notes
Transformers
The isolation characteristics of transformers are
superior to other balancing techniques for the
adverse and uncontrolled environments of field
production. Transformers provide complete galvanic
isolation from the driving source, meaning there is
no direct electrical connection. Signals are
“transformed” magnetically. Both the transformers
in the MP-1 use premium magnetic core material to
achieve high signal handling capability (especially at
low frequencies) 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.
Both the input and output of the MP-1 can be
balanced or unbalanced without any problems.
When unbalancing (either input or output) ground
pin 3 to pin 1. There is no change in gain with an
unbalanced connection into or out of the MP-1.
Phantom Power
Microphones that require phantom power should
use the lowest voltage acceptable to maximize
battery life. Electret-condenser microphones that
can operate on phantom voltages from 11-52 volts
will not have any performance benefit using 48-volt
phantom; therefore 12-volt phantom is appropriate.
Microphones requiring 48-volt phantom will not
operate, or may operate with lower headroom and
increased distortion, at 12 volts, therefore use 48-
volt phantom. Consult your microphone
documentation.
Dynamic microphones typically do not require
phantom power. A properly connected balanced,
dynamic microphone will, typically, 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 if the microphone cable is
suspect. Poor or incorrectly wired microphone cable
can cause audible artifacts in the microphone
signal. (Phantom is an excellent cable tester.)
High Pass Filter
The two positions of the high pass filter (low cut) in
the MP-1 are useful for removing excess low
frequency energy in the audio signal. 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
high pass filter is a single pole design, 6 dB per
octave.
When possible, attempt to equalize at the sound
source with microphone selection, use of a
windscreen, microphone placement, and onboard
microphone filtering. A high pass filter on the
microphone and a high pass filter on the MP-1 will
give an additive effect, increasing the slope of the
filter.
Limiter
The MP-1 has a built in peak responding limiter
which can be turned on or off by the switch on the
front panel. The MP-1 limiter is really two
completely separate limiters activated by the one
switch; the first limiter keeps the input gain stage
from clipping, and the second limiter limits the
output to +17 dBu. The two limiters enable the MP-
1 to limit in excess of 50 dB, meaning that it is very
difficult to clip the unit, no matter the gain setting.
The Limiter LED on the front panel illuminates in
proportion to the amount of limiting.
Batteries
The MP-1 is designed to operate on two AA alkaline
cells for approximately 26 hours with typical signals
(without phantom power). The audio performance
of the MP-1 does not vary throughout the life of the
batteries.
Many factors affect battery life including - battery
chemistry, ambient temperature of operation,
phantom voltage, microphone current draw, and
output drive level. The chart below can be used as
a starting point to estimate battery life.
Experimentation is recommended to determine
battery life for each individual setup. Note: Nickel-
Cadmium batteries are not recommended in the
MP-1 since these batteries have lower energy per
cell than other types and will result in very short
service.
Battery
Type Microphone
Type Battery
Life
Duracell AA
MN 1500 Dynamic handheld 26 hrs.
Duracell AA
MN 1500 Electret condenser, 12-volt
phantom 18 hrs.
Duracell AA
MN 1500 Studio condenser, 48-volt
phantom 5 hrs.
(Test conditions: 70 degrees F, 42 dB of gain with an acoustic
music source, 600 ohm load, +4 dBu output)
