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D90P Announce & Paging Microphone

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1597B Passive Monitor Panel

INSTALLATION AND OPERATION
The ALTEC D90P Announce and Paging Microphone is designed for service in all types of communications applications.The switch in the microphone handle has auxiliary contacts to operate additional equipment such as relays, lights, buzzers, etc.
The microphone cable consists of two shielded conductors and one unshielded conductor. The black and white shielded conductors carry the audio signal from the microphone to associated preamplifiers. The unshielded red conductor (with the shield as common) may be used for operating relays, indicator lights, buzzers, etc. As shown in Figures 4, 5 and 6, the red wire is disconnected from the shield when the microphone switch is "off". Placing the switch "on" connect,, the microphone element to the audio line and closes the additional switch contacts.
When a relay or other indicator is utilized, a 20 µF capacitor must be connected between the red lead and the shield, at the location of the relay (Figures 5 and 6) to prevent undesired switching transients ('popping') in the audio circuit.
The microphone switch may be held 'in' for short transmissions, or the switch may be pushed downward which locks it in the 'on' position. The mechanical construction of the switch is such that minimum mechanical sounds are transmitted through the amplification circuitry.
The microphone is threaded for 5/a"-27 mounts. Optional accessories include the Altec 34A Shock Mount Desk stand, to which the D90P may be easily attached.

SERIES CONNECTION:
When it becomes necessary to connect two or more microphones to a single input, without isolation of either input, a series arrangement such as that shown in figure 1 may be used. This method is preferred over the parallel arrangemerA shown in Figure 2 as the D90P switch need not be rewired.
In operation, all microphones are shorted out when no switches are open. When a single microphone is actuated, the short is removed from that microphone only and continuity is obtained through the remaining shorted switches to the amplifier input. If more than one microphone is in use simultaneously, continuity is obtained via both the shorted switches of the in-operative units, plus the transformer secondary of the additional operative microphone; such procedure may cause noticeable gain reduction when two or more microphones are used simultaneously.
1. Connect the white lead of the first microphone directly to the input of the
amplifier.
2. Connect the black lead of the last microphone to the amplifier.
3. Connect the black lead of the first microphone to the white lead of the second, as shown; continue this procedure until all microphones are wired in the illustrated series connection.

PARALLEL CONNECTION:
When microphones are connected in parallel, the switch must be rewired (Figure 2) so that the inoperative units are open-circuited when ''off" (not shorted out, as in normal or series connections).
In operation, only the microphone(s) switched "on" will furnish a completed circuit to the amplifier input; however, the remaining cable may act as a'floating' line and pick-up excessive hum and RF signals.
Experimentation has continually shown that, for optimum results, each microphone performs best when connected to a single input.
1. Remove the four screws which hold the escutcheon panel to the front of the
microphone handle; gently withdraw the panel and switch assembly so that the
contacts (on the rear of the switch) are accessible
2. Disconnect the black leads from the switch terminal; twist these leads together
and solder and tape.
3. Connect the yellow lead to the terminal formerly occupied by the black leads. 4. Move the white lead to the lower terminal.

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