Connections; Microphone Inputs (L And R); Balanced Xlr Outputs - Benchmark MPA1 Instruction Manual

Connections

Microphone Inputs (L and R)

The balanced transformerless microphone
inputs use locking Neutrik™ gold-pin female
XLR jacks with both pin 1 (Ground) and the
XLR shell directly bonded to the chassis. This
direct bonding is important for maximum RF
shielding and for immunity to hum due to
shield currents. Each input includes
Benchmark's precision-tuned, two-stage RF
filter for outstanding RF immunity.
XLR pin 2 = + Audio In
•
XLR pin 3 = - Audio In
•
XLR pin 1 = Cable Shield – bonded to
•
chassis
XLR shell – bonded to chassis
•
The microphone inputs have a wide operating
range. The maximum input level before
clipping is +29 dBu.
Each channel is equipped with a switch for
+48V phantom power. Under certain
circumstances, phantom power can cause
large voltage transients. The MPA1 is
equipped with high-current input protection
circuits that protect the sensitive low-noise
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 equipment (and your ears), we
strongly recommend shutting off phantom
MPA1 Instruction Manual
power several seconds before connecting or
disconnecting a microphone.
The MPA1 is designed to work with balanced
microphones, balanced line-level inputs, and
unbalanced sources as well. The MPA1
maintains rock-solid performance even in
difficult RF environments.
Common-mode signals in the audio band are
removed with a precisely trimmed differential
amplifier. The MPA1 even includes a subsonic
common-mode trim adjustment on each
microphone input that eliminates sensitivity
to +48V ripple caused by power supply noise
and/or the loading of microphone electronics.

Balanced XLR Outputs

The MPA1 has two balanced direct outputs.
These outputs use gold-pin Neutrik™ male
XLR connectors with direct chassis bonding of
both pin 1 and the connector shell. This
direct bonding is important for maximum RF
shielding and for immunity to hum due to
shield currents.
All outputs are transformerless and have an
impedance of 60 Ohms balanced or 30 Ohms
unbalanced. All outputs are equipped with
high-performance drivers that can drive high
signal levels into load impedances as low as
300 Ohms without an increase in distortion.
These outputs are well suited for driving long
lines.
XLR pin 2 = + Audio Out
XLR pin 3 = - Audio Out
XLR pin 1 = Cable Shield – bonded to chassis
XLR shell – bonded to chassis
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