LT0371 Issue 1.10 7 February 2018 Page 1 of 6
PA0688
Microphone Pre-Amplifier Module
Installation and Operating Instructions
Description
The PA0688 Microphone Pre-amplifier board is intended to provide emergency and non-emergency
microphone pre-amplification to “line” level with or without PTT function.
Overview
The PA0688 Microphone Pre-amplifier Module is designed for use with Vigilant EWIS systems; T-Gen2,
T-GEN 50 and QE90. It contains a microphone pre-amplifier with automatic level control, and two relays
which are operated by the PTT switch on the microphone. Refer to Figure 1.
The first relay switches the line level output between (a) line level input terminals (SPEECH IN) and (b) the
output of the pre-amplifier, and can be used to allow several PA0688 pre-amps to be connected in series to
the same panel input. The second relay is a two-pole changeover relay which can, for example, be used to
disconnect speakers in close proximity to the microphone when the microphone is in use to prevent audio
feedback. It can also be used for various other functions, e.g. to provide a switch input to a QE90 to indicate
that Paging is required.
Audio transformers should be used in conjunction with the PA0688:
for isolation, e.g. where the module is to feed multiple T-GEN units
for balancing, in order to reduce noise pickup in situations where long lines are to be used to feed
unbalanced inputs.
Refer to Figures 2, 6 and 7 for details.
SPEECH OUT
SPEECH IN
Relay Coils
+24V
0V
PTT Switch
PTT Out
MIC IN
SPARE
SPEAKER OUT
SPEAKER IN
Figure 1 - PA0688 Pre-amp Block Diagram
Connection and Operation
QE90
The PA0688 microphone pre-amplifier can be connected to the QE90 in many ways. One example is to
provide local paging to several QE90 amplifiers, using the QE90 amplifier local inputs. Refer to Figure 2.
In Figure 2 there are two pre-amps connected in a daisy chain so that either may be used. In the event of
PTT being pressed on both at the same time, the one closest to the QE90 will have priority. The connection
to the QE90 amplifier local inputs has been isolated by a transformer as these inputs are unbalanced and the
use of the transformer will provide a reduction in hum and noise. The SPKR IN+ and SPARE+ terminals on
the PA0688 have been used to obtain clean contacts which close when PTT is operated, and these have
been wired to a GP or FIP input on the QE90 that has been programmed by the manufacturer to disable
background music to the relevant amplifiers when the local paging is in use.
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All audio cables should be shielded and the shields connected to ground at the QE90.
MIC
PTT
QE90
Amplifier local input
SPEECH OUT
GP or FIP
Input
PA0688
SPKR IN +
SPARE +
SPEECH IN
0V+24V
SUPPLY
600 Ohm Line
Isolating
Transformer
Possible second
amplifier local input
PA0688
0V+24V
SPEECH OUT
SPEECH IN
SPKR IN +
SPARE +
SUPPLY
MIC
PTT
Figure 2 - Using PA0688 Pre-amp with QE90 Local Inputs
Note - An ALIM9706 could be used for the 600 Ohm Isolating Transformer. Refer to Figure 5.
Another example is shown in Figure 3. In this case the output of the pre-amp is connected to the QE90
MUSIC input, with the zones requiring paging field-programmed into the QE90. This example also shows
how the PA0688 can be used to disconnect speakers near the microphone to prevent feedback.
MIC
PTT
QE90
SPEECH OUT
PA0688
0V
+24V
SUPPLY
MUSIC IN
SPEECH IN
SPEAKER
OUTPUT
Speaker
Matching
Transformer
SPKR IN
Speaker Near
Microphone
Other Speakers
SPKR
OUT
Figure 3 - Using PA0688 Pre-amp with QE90 Music Input
NON-EMERGENCY MICROPHONE ON T-Gen2
T-Gen2 EWS has two audio inputs for connecting non-emergency background music sources or paging
facilities. The PA0688 microphone Pre-Amp can be used to boost a remote microphone voltage to feed into
the T-Gen2 Audio Input for remote paging.
The Pre-Amp needs to be located with the microphone and is supplied with 24Vdc power. Figure 4 shows
the wiring arrangement.
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Note: Screened cable should be used for the audio connections between pre-amp modules and the T-
Gen2, with the screen connected to the 0V input at the T-Gen2. The paging microphone closest to
the T-Gen will have priority if both microphone PTT buttons are pressed at the same time.
The 24V feed for the Pre-Amps should be separately fused so a fault does not remove power to
the T-Gen2.
SPEECH OUT+
SPEECH OUT-
PA0688 MICROPHONE PRE-AMP
SPEECH IN+
SPEECH IN-
SPEAKER OUT+
SPARE+
24V+
0V
PTT0V
MIC
+
-
SPEECH OUT+
SPEECH OUT-
PA0688 MICROPHONE PRE-AMP
SPEECH IN+
SPEECH IN-
SPEAKER OUT+
SPARE+
24V+
0V
PTT0V
MIC
+
-
AUD IN+
AUD IN-
T-Gen2
0V
GP IN
0V
+24V
Figure 4 – Microphone Pre-Amp to T-Gen2
T-GEN 50
Output Level
The PA0688 can be used for paging facilities to boost the voltage from a microphone to the T-GEN's music
input.
In standard form, the PA0688’s output does not provide the 2.5-3V RMS signal level required by the Music
Input of T-GEN 50. To solve this, resistor R28 on the PA0688 Microphone Pre-amp should be changed to
10k.
Wiring - Non-Emergency Microphone
One or more PA0688 Microphone Pre-amps can be wired to the T-GEN as in Figure 5.
Screened cable should be used for the audio connections between pre-amp modules and the T-GEN, with
the screen connected to the 0V input (Pin 2) of J9 at the T-GEN. The paging microphone closest to the TGEN will have priority if both PTT buttons are pressed at the same time.
PA0688 MICROPHONE PREAMP
MIC
OUT+
IN+
0V
SPEECH OUT+
SPEECH IN +
R28=10k
PA0688 MICROPHONE PREAMP
MIC
OUT+
IN+
PTT-
0V
SPEECH OUT+
SPEECH IN+
R28=10k
MUSIC
1
2
+24V
0V
24V POWER
T-GEN
+
+
-
-
OPTIONAL
(REPEAT FOR FURTHER
MICROPHONES)
J9
0V
+24V
+24V
0V
0V
PTT-
Figure 5 - Unbalanced Configuration, PA0688 to T-GEN 50, Non-emergency Microphone
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If the T-GEN and pre-amp(s) are not mounted close together then to increase immunity to any ambient
electrical noise, it is recommended that screened cable should be used and an ALIM9706 should be located
at the T-GEN input. This is shown in Figure 6.
Note that the segments of screened cable connecting the pre-amp modules to the T-GEN must have their
shields wired together and connected to the 0V input of J9 (Pin 2) or J1 at the T-GEN. Again the paging
microphone closest to the T-GEN will have priority if both PTT buttons are pressed at the same time.
Note that there are volume controls on both the ALIM and pre-amps(s), we recommend setting the ALIM
volume to maximum and adjusting each microphone separately at its pre-amp.
Figure 6 - Balanced Configuration, PA0688 to T-GEN 50, Non-emergency Microphone
Emergency Microphone For T-GEN
In the above arrangements, the remote microphone will not override tones, digitised speech, or PA
messages generated by the emergency microphone plugged into connector J1.
For an emergency microphone located at the T-GEN a suitable pre-wired handheld microphone with PTT
switch and plug is available (ME0290).
For remotely located emergency microphone(s) we suggest the arrangement shown in Figure 7.
Note that the segments of screened cable connecting the pre-amp modules to the T-GEN must have their
shields wired together and must be connected to the 0V input of J9 (Pin 2) or J1 at the T-GEN. Again, the
microphone closest to the T-GEN will have priority if both PTT buttons are pressed at the same time.
Note that there are volume controls on both the ALIM and pre-amps(s). We recommend setting the ALIM
volume to maximum and adjusting each microphone separately at its pre-amp.
PA0688 MICROPHONE PRE-AMP
SPEECH OUT+
SPEAKER IN +
SPEECH OUT
SPARE -+
MIC SPEECH IN +
SPEECH IN -
+24V
PTT-
0V
PA0688 MICROPHONE PRE-AMP
SPEECH OUT+
SPEECH OUT MIC
+24V
PTT-
0V
PA0846/646 ALIM
A+
A-
A-
A+
INPUT
OUTPUT
+24V
0V
T-GEN
24V Power
SHIELD
OPTIONAL
(Repeat for further microphones)
+
+
-
-
0V
0V
SPEAKER IN +
SPARE +
47k
47k
MIC+
MIC-
PTT0V
LK1A, LK2A NOT FITTED, LK3A FITTED 2-3
J1
Figure 7 - Remote Emergency Microphone(s) for T-GEN 50
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PA0688 Specifications
Board Dimensions:
157 x 93 x 25mm (lwh)
Shipping Weight:
0.25kg
Temperature:
Operating 0ºC – 45ºC
Storage 0ºC – 70ºC.
Humidity:
<95% relative humidity (non-condensing)
Operating Voltage:
24V (17-28V) from panel.
Operating Current:
35mA (55mA PTT operated)
Output: (1 khz test tone)
500-700 mV RMS for 1mV in @<10% distortion
600-800 mV RMS for 10mV in @<1% distortion
600-1000 mV RMS for 40mV in @<1% distortion
Nominal Output Impedance:
600 Ohm
Inputs:
MIC+, MIC-, PTT-, +24V (supply)
Microphone Input:
Suitable for dynamic microphone, 600 Ohm
nominal @ 1kHz
Accessories included with PA0688
None.
ME0290 is a suitable PTT microphone (ordered separately).
LT0371 Issue 1.10 7 February 2018 Page 6 of 6
Manufactured
Johnson Controls
Distributed
by:
17 Mary Muller Drive, PO Box 19-545
by:
Christchurch, New Zealand
Tel +64-3-389 5096
Fax +64-3-389-5938
© 2017. Johnson Controls. All rights reserved. All specifications and other information shown were current as of document revision
date and are subject to change without notice.
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