Architect’s and Engineer’s Specication
The mono mixer-amplier shall be equipped with six unbalanced
stereo music inputs on phono sockets (RCA jacks) and four balanced
microphone inputs on multipin connectors. The music input to be
used shall be selectable by a 6-position front panel rotary switch. The
four mic inputs shall be mixed to a mono signal and summed with a
mono (L+R) sum of the selected music input. Each mic input shall have
its own front panel level control. It shall be possible to control the
level of the music source independently of the mic levels. Each music
input and each mic input shall also have a rear panel gain control.
2-band equalisation adjustment shall be provided independently for
the selected music source and summed mic signals.
A control input shall be provided to activate one mic input
(Mic 1) by external contact closure; it shall be possible to congure
the mixer-amplier such that this function is overriden and Mic 1 is
always active. It shall be possible to congure the mixer-amplier
to perform the following additional functions: i) when activated by
its control input, Mic 1 will take priority over any other mic input
in use; ii) detection of a signal on any mic input will automatically
reduce the music level by 30 dB, iii) one line input will automatically
override all others, even if unselected. Optional remote control
panels shall be available to permit control of music level only or
music level and input selection; it shall be possible to retrot these
to the mixer-amplier at any time. An external control input shall
be provided to allow muting of the music source by a re alarm or
other external emergency system. The mixer-amplier will include a
chime generator circuit triggered by a signal on Mic 1 input; it shall be
possible to internally disable/enable this function. It shall be possible
to recongure Mic 1 input as a galvanically-isolated input suitable for
connection to compatible telephone systems; the sensitivity of the
input shall be reduced by 10 dB in this mode and the input shall be
optimised for connection to a source impedance of 600 ohms.
The microphone mixer stage shall include a high-pass lter to
remove background LF noise below 100 Hz (-3 dB). A second high-
pass lter shall be included to remove LF content below 65 Hz
(-3 dB) from the mixed music and mic signals to minimise transformer
saturation in 100/70/25 V-line systems; this lter shall be internally
by-passable. Two separate internal xed limiter circuits shall be tted;
these shall be located at i) the output of the microphone mixer
stage and ii) at the input of the power amplier stage. Operation
of either limiter shall be indicated by a front panel LED. The mixer-
amplier shall incorporate protection circuitry that isolates the
output i) during power-up, ii) in the event of DC being detected at
the amplier output, iii) if the internal heatsink temperature exceeds
90°C (194°F).
The mixer-amplier shall be available in two models with different
output powers of 120 W or 240 W, into a 4 ohm load. The mixer-
amplier shall be capable of driving either low impedance (4 ohms
or higher) loads, or 100 V-line, 70 V-line or 25 V-line line systems via
an internal transformer tted as standard. It shall not be possible to
use both types of output simultaneously. The 100 V, 70 V and 25 V
transformer outputs shall be available on separate rear panel output
terminals, shrouded by a screw-attached safety cover.
The mixer-amplier shall provide two secondary outputs from the
pre-amplier stages: i) a balanced line level output taken from the
output of the power amplier input limiter stage; ii) an output taken
from the mixer section with separate controls of the preset type for
setting the levels of the music and microphone mix components of
the output signal. This output shall be available in both unbalanced
line level form and as a galvanically-isolated signal suitable for
connection to the Music On Hold input of compatible telephone
systems having an minimum input impedance of 600 ohms. It shall be
possible to congure the music source for this output to be either
permanently Line Input 6 or follow user source selection made on
the front panel or via a remote control plate.
The mixer-amplier shall accept internal plug-in equaliser cards to
permit use with compatible loudspeakers from various manufacturers.
The mixer-amplier shall be built in a 2U steel chassis for mounting
in a standard 19” rack.Temperature-controlled forced-air fan cooling
with front-to-rear airow shall be employed. The amplier will be
tted with a front-panel power switch with LED indication.
The mixer-ampliers shall be the Cloud MPA120 (120 W output)
and the Cloud MPA240 (240 W output). The remote control plates
shall be the Cloud RL-1 Series (music level only) and the Cloud
RSL-6 Series (music level and source selection).
Cloud Electronics Limited
140 Staniforth Road, Shefeld, S9 3HF. England.
Telephone: +44 (0)114 244 7051 Fax: +44 (0)114 242 5462
Cloud Electronics USA
2065 Sidewinder Drive, Suite 200, Park City,
Utah 84060. United States of America.
Toll Free: 0855 810 0161
