13
Audio Input
The PSW-6 uses a 10 kΩ balanced input imped-
ance 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.
TROUBLESHOOTING NOTE: Shorting an input con-
nector pin to the case can form a ground loop and
cause hum. If other abnormal noises (hiss, pop-
ping) are produced from the loudspeaker, discon-
nect the audio source from the speaker. If the noise
stops, then the problem is not within the loud-
speaker; check the audio input and AC power.
A single source can drive multiple PSW-6s with a
paralleled input loop, creating an unbuffered hard-
wired loop connection. Make certain that the source
device can drive the total load impedance pre-
sented by the paralleled input circuit. For ex-
ample, since the input impedance of a single
PSW-6 is 10 kΩ, cascading 20 units produces a
balanced input impedance of 500Ω. If a 150Ω
source is used, the 500Ω load results in a 2.28 dB
loss.
Amplification and
Protection Circuitry
The PSW-6 is powered by the Meyer MP-4, a
four-channel 2480 Watt amplifier (620 W/ch) uti-
lizing complementary power MOSFET output stages
(class AB/H). The following sections discuss the
MP-4s limiting circuitry and four-fan cooling sys-
tem.
The TruPower Limiting System
Conventional limiters assume that the resistance
of a speaker remains constant and set the limiting
threshold by measuring voltage only. This method
is inaccurate because the speakers resistance
changes in response to the frequency content of
the source material and thermal variations in the
speakers voice coil and magnet. Conventional
limiters begin limiting prematurely, which under-
utilizes system headroom and deprives the speaker
of its full dynamic range.
The TruPower Limiting (TPL) system accounts for
varying speaker impedance by measuring cur-
rent, in addition to voltage, to compute the actual
power dissipation in the voice coil. TPL
improves performance before and during
limiting by allowing each driver to produce
its maximum SPL across its entire frequency
range;
protects the drivers by controlling the tem-
perature of the voice coil;
eliminates long-term power compression when
the system is operated at high levels for
extended periods.
The PSW-6 performs within its acoustical specifi-
cations and operates at a normal temperature if
the limit LEDs are on for no longer than two
seconds, and off for at least one second. If either
LED remains on for longer than three seconds,
that channel is hard limiting with the following
negative consequences:
Increasing the input level will not increase
the volume.
The system distorts due to clipping and non-
linear driver operation.
Unequal limiting between the low and high
channels alters the frequency response.
The life-span of the drivers is reduced be-
cause they are subjected to excessive heat.
Serious degradation of the cardioid response
pattern.
NOTE: Although the TPL limiters exhibit smooth sonic
characteristics, we do not recommend using them for
intentional compression effects. Use an outboard com-
pressor/limiter to compress a mixed signal.
Differential Inputs
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