Phantom Power Switches; Input Protection; Polarity Switch; 40 Hz High-Pass Filters - Benchmark MPA1 Instruction Manual

Phantom Power Switches

Up = Phantom On
Down = Phantom Off
CAUTION: ALWAYS TURN OFF PHANTOM
POWER AND WAIT SEVERAL SECONDS
BEFORE CONNECTING OR
DISCONNECTING MICROPHONES.
The MPA1 has an internal 'Phantom Defeat'
jumper. When this jumper is removed,
phantom power cannot be applied to the
respective microphone input. This feature
should be used when the MPA1 is dedicated
to ribbon microphone. The purpose is to
protect the ribbon element in case the +48V
switch is thrown. The internal 'Phantom
Defeat' jumper is located behind the left
channel's +48V switch (bottom-left in the
following picture).
CAUTION: ALWAYS DISCONNECT POWER
FROM THE MPA1 FOR FIVE MINUTES
BEFORE ADJUSTING THE PHANTOM
DEFEAT JUMPER.
MPA1 Instruction Manual

Input Protection

Under certain circumstances, phantom power
can cause large voltage transients. The MPA1
is equipped with high-speed, high-current,
low-capacitance protection circuits that
protect the sensitive input-transistors from
the worst-case phantom-induced transients.
Large transients are produced when a
microphone is connected or disconnected
while phantom power is on. The worst
possible transients occur when a microphone
cable has an intermittent short to ground
from either pin 2 or pin 3. The MPA1 is very
well protected against both of the above. For
the protection of your microphones (and your
ears), we strongly recommend shutting off
phantom power several seconds before
connecting or disconnecting a microphone.

Polarity Switch

Up = Polarity is Inverted
Down = Polarity is Normal
The polarity switch allows the polarity of the
input signal as to be easily reversed. Typical
applications that require polarity inversion
include using the back-side of a figure-8
microphone (such as a ribbon), having two
microphones on one instrument but facing
opposite directions, or when a microphone or
cable is constructed with inverted polarity.

40 Hz High-Pass Filters

Up = Filter Enabled
Down = Filter Off
The 40 Hz high-pass filter is a second-order
filter with a slope of 12 dB per octave. This
filter is intended to remove unwanted
subsonic noise and rumble caused by sources
such as HVAC, air currents, and vibration.
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