Page 9 of 12 DocNo.DCP0001326 DSM 05/01/05 rev7
The amplifier may be used in conjunction with 100
Volt constant voltage loudspeaker systems. This
technique is ideal in public address applications
where it is necessary to operate loudspeakers
over a distance from the amplifier as it prevents
excessive line losses. Line matching transformers
must be installed at each loudspeaker to match them to the amplifier. Low ohm speakers will sound distorted.
This is similar in principle to mains electricity distribution where power is transformed to high voltages and
sent long distances over small conductors before being transformed down again at its destination(s).
These constant voltage outputs are most convenient for distribution of power when a number of speakers are
installed. Each loudspeaker must have a 100 Volt line transformer with a tap that gives the power desired for
that loudspeaker. The total number of power settings for all speakers should be equal to the amplifier power
rating or less. See the following diagrams.
100 Volt connection (200 Watt)
100 Volt connection (400 Watt)
Operation and Set-up
Once an amplifier is installed and powered up, it is necessary to adjust or verify the following
settings:
1. Ensure that an audio lead from a SigNET routing matrix is connected to both Main Inputs a.
2. Check that the monitoring tone is not disabled (the tone fail (TF) indicator is not lit).
3. No audio should be routed into the Main input except for the 22 kHz monitoring tone
4. Using an oscilloscope (e.g. Maplin Part No.IN02158) or true r.m.s voltmeter (RS218-0265) capable of
reading up to 25 kHz, connect to each 100V line output across 0V + 100V. Adjust the main level control
to give a reading of 6 Volts Peak to peak (2.12 Volts r.m.s)
NB
Default factory setting is 0V (off), other than on full System deliveries.
5. Once set, this level control must not be adjusted again – all level adjustments must be carried out
by altering the levels from the source equipment (matrix).
Set-up the load monitoring circuit is as follows;
6. Turn the Threshold and Windows controls to minimum (anticlockwise). Ensure load and End of line
(EOL) unit are connected. If loudspeaker splitters are used there must be an end of line unit on each
spur. If more than two end of line units are fitted, the monitoring system will not operate reliably.
7. Turn up the threshold control clockwise until the Load Hi and Load low LED’s are just toggling.
8. Open window control fully (clockwise).
9. Remove the EOL unit. Load Hi should come, and remain on.
10. Refit EOL, Load Hi LED should extinguish.
Note
Loudspeaker runs of more than 400m are not recommended, as faults cannot be reliably
detected.
Output connections
Output socket
