Chapter 3: Amplification And Audio; Audio Input Modules - Meyer Sound UPJunior UltraCompact VariO Operating Instructions Manual

CHAPTER 3: AMPLIFICATION AND AUDIO

The low- and high-frequency drivers in the UPJunior are
powered by a two-channel proprietary Meyer Sound ampli-
fier with MOSFET output stages. The audio signal is pro-
cessed with an electronic crossover, correction filters for
phase and frequency response, and driver protection cir-
cuitry. Each channel has peak and rms limiters that prevent
driver over-excursion and regulate the temperature of the
voice coil.
The user panel on the back of the UPJunior has two slots for
modules. The top slot contains an audio input module
(described in this chapter). The bottom slot is reserved for
the optional RMS module, used for connecting to the RMS
remote monitoring system (see Chapter 7, "The RMS
Remote Monitoring System").

AUDIO INPUT MODULES

The UPJunior can be equipped with either of two audio
input modules: The Looping Audio Input module or the
Looping, Polarity, and Attenuating Audio Input module. Both
audio input modules have input and looping connectors,
and LEDs for monitoring temperature and limiting. In addi-
tion, the Looping, Polarity, and Attenuating Audio Input
module has a switch for swapping the signal's polarity, and
a knob for attenuating the input signal level to –18 dB.
The Looping Audio Input Module
The Looping Audio Input module includes the following con-
nectors and LEDs.
Looping Audio Input Module
Input Connector
The female XLR Input connector accepts a balanced audio
signal with an input impedance of 10 kOhm. The connector
uses the following wiring:
Pin 1 — 220 kOhm 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. Pin 1 is
connected to earth through a 220 kOhm, 1000 pF, 15 V
clamped network. This circuitry provides virtual ground lift
for audio frequencies while allowing unwanted signals to
bleed to ground. Make sure to use standard, balanced XLR
audio cables with all three pins connected on both ends.
Telescopic grounding is not recommended, and shorting an
input connector pin to the case may cause a ground loop,
resulting in hum.
TIP: If unwanted noise or hiss is produced by
the loudspeaker, disconnect its input cable. If
the noise stops, there is most likely nothing wrong
with the loudspeaker. To locate the source of the
noise, check the audio cable, source audio, and AC
power.
Loop Connector
The male XLR Loop connector allows multiple UPJuniors to
be looped from a single audio source. Connect the Loop
output of the first UPJunior to the Input of the second
UPJunior, and so forth. The Loop connector is wired in par-
allel to the Input connector and transmits the unbuffered
source signal even when the UPJunior is powered off.
To avoid distortion when looping multiple UPJunior loud-
speakers, make sure the source device can drive the total
load impedance of the looped loudspeakers. The source
device must be capable of delivering a minimum of 20 dBV
(10 V rms into 600 ohms) to yield the maximum peak SPL
over the operating bandwidth of the loudspeaker.
To calculate the load impedance for the looped loudspeak-
ers, divide 10 kOhms (the input impedance for a single
UPJunior) by the number of looped loudspeakers. For
example, the load impedance for 10 UPJuniors is
1000 Ohms (10 kOhms / 10). To drive this number of looped
loudspeakers, the source device should have an output
impedance of 100 ohms or less. This same rule applies
when looping UPJuniors with other self-powered Meyer
Sound loudspeakers and subwoofers.
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