Cloud Electronics MPA60 - Manual (Page 9)

MPA Series User Manual v1.2 9
ideally by the people who will normally make them. The Mic
EQ should be adjusted if necessary to maximise voice clarity.
Microphone Priority
MPA Series mixer-amplifiers provide two separate
microphone priority functions. One of these enables the
microphones to have priority over music, the other allows
Mic 1 to have priority over the other microphones.
Microphone over music priority
Fully automatic voice operated priority (VOX function) is
available for the microphone signals. This function is enabled
by internal jumper J6 (default setting is ON). When enabled,
the music signal is automatically attenuated by 30 dB when
a microphone signal is detected, allowing the message to be
clearly heard. Normal music operation is restored smoothly
after the announcement ends.
Note that the presence of a signal on any of the four mic
inputs will operate this function.
Mic 1 over Mics 2-4 priority
If internal jumper J8 is set to ON (the default setting is
OFF), Mic inputs 2, 3 and 4 will be muted whenever the
Microphone Access Input is enabled. This ensures that Mic 1
will always have priority over any other microphones in use
when Mic 1 is used for paging.
Note that if jumper J13 is left at its default setting of ON,
Mics 2, 3 and 4 will be permanently disabled by this function,
leaving Mic 1 as the only active microphone input.
Chime
The MPA Series amplifiers have an internal pre-
announcement chime generator. The chime is triggered by
the Microphone Access Input, if enabled by jumper J1 being
set to ON. J1’s default setting is OFF.
An internal preset rotary control is provided to adjust the
chime volume; the front panel level controls have no effect
on the chime level. See fig.7 for locations of internal controls.
Power Amplifier Stage
and Outputs
Line Output
The MPA Series amplifier’s output stage incorporates
an output transformer suitable for driving 100 V, 70 V or
25 V line speaker distribution system. The secondary (output
side) of the transformer is permanently wired to the line
output connector (a 4-pin 5 mm-pitch screw terminal type).
A safety cover is fitted over the connector, which may be
removed to connect the speaker cable. Replace the cover
after the connection has been made.
The transformer secondary has 3 line outputs: 100 V, 70 V
and 25 V; while these have a common 0 V connection, the
output is fully floating i.e., it is isolated from the rest of the
amplifier. The maximum total combined load should not
exceed the rated power for the amplifier model (see table
below).
When driving 100/70/25 V line circuits, it is strongly
recommended that the amplifier’s 65 Hz high pass filter is
set ON (see High pass filter - page 10).
Low impedance operation
To convert the amplifier to low impedance operation, the
primary winding of the toroidal transformer nearer the
rear of the unit should be unplugged from CON8 on the
main pcb (a short pair of heavy red and black wires), and
replaced by the spare plug connected to the rear panel low
impedance output socket (same wire types). Refer to fig. 7
(page 13) for the location of this connector. Note that the
100/70/25 V line outputs will no longer be available once
the transformer is unplugged even though the transformer
secondary is still connected to the line output connector.
The low impedance output is available on a 2-pin 5 mm-pitch
screw terminal connector on the rear panel. Note that one
of the output pins is connected internally to 0 V.
The MPA Series amplifiers are able to deliver their rated
power into a 4 ohm load, as follows:
Model Rated Power
MPA60 60 watts
MPA120 120 watts
MPA240 240 watts
The maximum output power will be reduced with higher
load impedances. When using multiple low-impedance
loudspeakers (normally 8 ohms) with a single amplifier, series
and parallel wiring should be employed to produce a total
load impedance of not less than 4 ohms.