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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-ampliers 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 ampliers 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 g.7 for locations of internal controls.

Power Amplier Stage

and Outputs

Line Output

The MPA Series amplier’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 tted 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 oating i.e., it is isolated from the rest of the

amplier. The maximum total combined load should not

exceed the rated power for the amplier model (see table

below).

When driving 100/70/25 V line circuits, it is strongly

recommended that the amplier’s 65 Hz high pass lter is

set ON (see High pass lter - page 10).

Low impedance operation

To convert the amplier 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 g. 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 ampliers 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 amplier, series

and parallel wiring should be employed to produce a total

load impedance of not less than 4 ohms.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

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