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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. Be-
cause 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 un-
balancing (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. Micro-
phones 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, dy-
namic 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. (Phan-
tom 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 fre-
quency 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.
