Amplification And Limiting - Meyer Sound UPM-1P Operating Instructions Manual

CHAPTER 2
Looping, Polarity and Attenuating Audio Input
Module
The looping, polarity and attenuating audio input mod-
ule (Figure 2.3) has a balanced, female XLR audio input
connector, a male XLR loop connector, an input polarity
switch, and a level attenuator. The input polarity switch
offers a convenient method of reversing the polarity of the
loudspeaker. The loop out remains unchanged.
GND 1 1
Circuit 2 2
3 3
220k
Case
Earth /
Chassis
Input Loop
Figure 2.3. The looping, polarity and attenuating audio input module
When the input polarity switch is in the up ( + ) position, pin
2 is hot. When the switch is down ( - ), pin 3 is hot relative
to pin 2, resulting in a positive pressure wave when a posi-
tive signal is applied to pin 3. The level attenuator operates
between 0 dB (no level attenuation) when turned all the way
to the right and –18 dB when turned all the way to the left.
NOTE:
In both modules, Pin 1 is connected
to earth through a 220 kOhm, 1000 pF, 15-
volt clamp network. This ingenious circuit provides
virtual ground lift at audio frequencies, while
allowing unwanted signals to bleed to ground.
Use standard audio cables with XLR connectors
for balanced signal sources with all three pins
connected on both ends. Telescopic grounding is
not recommended.
Regardless of the input module type, audio signals can be
daisy-chained using the loop output connector on the user
panel. A single source can drive multiple loudspeakers with
a paralleled input loop, creating an unbuffered hard-wired
loop connection. If driving multiple loudspeakers in a sys-
tem, make certain that the source device can drive the total
load impedance presented by the paralleled input circuit of
the system. The audio source must be capable of providing
a minimum of 20 dB volts (10 volts rms into 600 ohms) to
produce the maximum peak SPL over the operating band-
width of the loudspeaker.
To avoid distortion from the source, make sure the source
equipment provides an adequate drive circuit design for the
total paralleled load impedance presented by the system.
The input impedance for a single loudspeaker is 10 kOhms.
If n represents the number of loudspeakers in a system,
paralleling the inputs of n loudspeakers will produce a bal-
anced input load of 10 kOhms divided by n.
10
Looping Polarity & Attn. Audio Input
10k Balanced
+
-
-
9
- -
12 6
-
-
3
15
Polarity
+ Limit
- -
0
18
Attn dB
On / Temp.
NOTE: Most source equipment is safe for
driving loads no smaller than 10 times the
source's output impedance.
For example, cascading an array of 10 loudspeakers
produces an input impedance of 1000 ohms (10 kOhms
divided by 10). The source equipment should have an out-
put impedance of 100 ohms or less. This is also true when
connecting UPM-1P or UPM-2P loudspeakers in parallel
(loop out) with other self-powered Meyer Sound loudspeak-
ers and subwoofers
TIP:
If the loudspeaker produces hissing
and popping or similar noises, disconnect
the audio cable from the loudspeaker. If the noise
stops, then most likely the problem is not with the
loudspeaker. Check the audio cable, source, and
AC power.
AMPLIFICATION AND LIMITING
The low- and high-frequency drivers in the UPM-1P and
UPM-2P loudspeakers are powered by a two-channel
proprietary Meyer Sound amplifier utilizing complementary
MOSFET output stages. The amplifier processes the audio
through the use of electronic crossover, phase and frequen-
cy response correction filters as well as driver protection
circuitry. Each channel has peak and rms limiters that pre-
vent driver over-excursion and regulate the temperature of
the voice coil. Limiter activity for the high and low channels
is indicated by two yellow limit LEDs on the rear panel (the
high-frequency limit LED is on top and the low-frequency
limit LED is on bottom).
CAUTION: Although the UPM-1P and
!
UPM-2P use the same amplifier/heatsink
module, their internal control boards are different.
In order to maintain factory acoustical specifications
and driver protection (as well as keep from voiding
the factory warranty), never interchange the ampli-
fiers used in the UPM-1P and UPM-2P. If you need
to replace a UPM-1P or UPM-2P amplifier and/or
control board, please contact Meyer Sound.