MPA685 Owner’s Manual
3/2012
9
INSTRUCTIONS FOR USE
1. AC Power
AC power is applied through an IEC 320-C16 (Male Pins) connector with earth ground.
An AC fuse is contained in the connector. The fuse holder can be removed when AC
power is unplugged from the unit. Use a flat blade screwdriver to remove the fuse
holder from the unit.
Use only a 500mA slow blow fuse.
2. Turning Power On and Off
The power supply is designed to ramp the DC voltage slowly when the power switch is
turned on and off, and power-on/off transients are minimal. However, for good practice,
reduce the studio volume before turning power on or off.
After power up, please allow approximately 5 minutes time for component warm up and
stabilization time for the electronics before beginning critical listening or recording.
3. Audio Connections
Audio microphone input and output connections are made with standard ITT Cannon
XLR 3-31 and 3-32 types. XLR audio input and output connections are balanced, with
pin 2 positive, Pin 3 negative and Pin 1 ground. A ground lift toggle switch is included
on the back panel to isolate XLR connector Pin 1 from chassis ground should hum be
encountered. Note that both input and output Pin 1 is permanently connected to audio
ground for maximum stability with highest gain settings. Should output connector Pin 1
need to be fully disconnected from the pre-amplifier, this is best accomplished by
disconnecting Pin 1 in the XLR cable connected to the pre-amplifier output.
Your unit is configured with an extra ¼” phone jack on the back panel, labeled “Opt”. It
is hardwired to the XLR input connector. The ¼” jack is wired for Tip = Hot, Ring = Cold
and Sleeve = Ground.
This extra input can be used as a microphone signal loop-through for mic splitting
applications. Simply use a TRS ¼” balanced cable to connect Channel 1 “Opt” jack to
Channel 2 “Opt” jack, and the mic signal is effectively split to Channels 1 & 2
simultaneously.
