5
Differential Inputs
Audio Input
The PSM-2 presents a 10 kΩ input impedance to a three-
pin XLR connector wired with the following convention:
Pin 1 — 220 kΩ to chassis and earth ground (ESD clamped)
Pin 2 — Signal
Pin 3 — Signal
Case — Earth (AC) ground and chassis
Pins 2 and 3 carry the input as a differential signal;
their polarity can be reversed with the input polarity
switch on the user panel. If the switch is in the up
position, pin 2 is hot relative to pin 3, resulting in a
positive pressure wave when a positive signal is applied
to pin 2. Use standard audio cables with XLR connectors
for balanced signal sources.
Shorting an input connector pin to the case can
form a ground loop and cause hum.
A single source can drive multiple PSM-2s with a
paralleled input loop, creating an unbuffered hard-
wired loop connection. Make certain that the source
equipment can drive the total load impedance presented
by the paralleled input circuit. For example, since the
input impedance of a single PSM-2 is 10 kΩ, cascading
20 PSM-2s produces a balanced input impedance of
500 Ω. If a 150 Ω source is used, the 500 Ω load results
in a 2.28 dB loss.
Troubleshooting
If the Active lamp does not light after connection to an
AC source for three seconds, the problem is probably in
the power supply. In the unlikely case that the circuit
breakers trip (the white center buttons pop out), the
amplifier or power supply may be malfunctioning.
Do not reset the breakers! Contact Meyer Sound for repair
information.
If abnormal noise (hum, hiss, popping) is produced
from the loudspeaker, disconnect the audio source
from the speaker. If the noise stops, then the problem
is not within the loudspeaker; check your audio and
AC power sources.
If problems persist, contact Meyer Sound. If repairs are
necessary, the PSM-2’s modular components are easy
to remove and ship.
Safety Issues
Pay close attention to these important electrical and
safety issues.
Use a power cord adapter to drive the PSM-2
from a standard 3-prong outlet (NEMA 5-15R;
125 V max).
earth
ground
chassis
ground
The PSM-2 requires a grounded outlet. Always
use a grounding adapter when connecting to
ungrounded outlets.
Do not use a ground-lifting adapter or cut the
AC cable ground pin.
Keep all liquids away from the PSM-2 to avoid hazards
from electrical shock.
Do not operate the unit if the power cables are frayed
or broken; replace worn or damaged cables immediately.
Tie-wrap anchors on the amplifier chassis provide
strain relief for the power and signal cables. Insert the
plastic tie-wraps through the anchors and wrap them
around the cables.
The PSM-2 should not be installed outdoors without
weather protection. The cabinet, exposed electronic
circuitry, and drivers can all receive weather protection
treatment that allows the unit to be used safely in wet
conditions. Contact Meyer Sound for information
about weather-protected units.