The document is a user manual for the PS 285 Power Supply Booster. It contains sections describing: 1. The general description and purpose of the PS 285 as an auxiliary power supply for expanding the capacity of an existing intercom system. 2. Unpacking instructions and contents of the packaging for the PS 285. 3. Installation instructions for the PS 285 including mechanical installation, mains power connection, and set-up within an intercom network.

1. PRO SERIES
USER MANUAL
FOR THE
PS 285
POWER SUPPLY BOOSTER
over
load
Pro series
PS 285
On Standby On Standby
Power
Supply
Booster
Power Intercom
CHANNEL A CHANNEL B
CONTENTS
1.0 GENERAL DESCRIPTION ..........................................3
2.0 UNPACKING ...............................................................3
3.0 MECHANICAL INSTALLATION...................................3
4.0 MAINS POWER ..........................................................4
5.0 SET-UP .......................................................................4
6.0 FRONT PANEL CONTROLS.......................................5
7.0 REAR PANEL CONTROLS AND CONNECTORS.......6
8.0 CABLING.....................................................................7
9.0 PARTY LINE, TECHNICAL CONCEPT .......................8
10.0 GUARANTEE ..............................................................8
11.0 TECHNICAL SPECIFICATIONS..................................8
User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.

2. 2 User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.

3. 1.0 GENERAL DESCRIPTION
The PS 285 is designed for use as an auxiliary 2-channel The intercom line power supply is fully protected and is
power supply unit, should the main power supply of an capable of safely driving 20 beltpacks or 10 speaker
ASL intercom system be insufficient to drive the required stations, or a combination of the two, operating at full
number of stations. power.
The unit has to be placed in a network in such a way that
it feeds its own group of user stations. Fully electronic switching increases reliability and allows
The PS 285 can be used in portable as well as fixed for remote Mic Mute facility.
applications. It uses only 1U of 19” rack space.
The unit is very versatile and ideal for use in applications
where standard microphone cable is available and ease of
set-up is of paramount importance.
2.0 UNPACKING
The shipping carton contains the parts listed below ASL has taken great care to ensure that this product
reaches you in flawless condition.
* The PS 285 After unpacking the unit please inspect for any physical
* Mains power cable damage to the unit, and retain the shipping carton and
* Spare fuses relevant packing materials for use should the unit need
* User manual returning.
If any are missing, contact your dealer. If any damage has occurred, please notify your dealer
immediately so that a written claim can be initiated.
With the PS 285 will be a small packet of spare fuses. Please also refer to the guarantee section of this manual.
Please keep them in a safe place.
There is also one spare fuse included in the mains inlet.
3.0 MECHANICAL INSTALLATION
A vertical rack space of 1U (1.75”, 44mm) is required for The power supply regulator is mounted on the rear of the
the PS 285. It is not necessary to provide rear support by unit, and after a period of time it will feel hot to the touch.
extra bracing or shelving. This is quite normal, and should be no cause for alarm.
Adequate ventilation must be provided by allowing
sufficient space around the sides and rear of the unit to
ensure free circulation of air. Forced cooling is not
required.
User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands. 3

4. 4.0 MAINS POWER
The PS 285 may be connected to the mains
power outlet to which other audio equipment is
connected. The outlet should have a clean earth.
Avoid using mains power outlets which also power
dimmer controlled lighting equipment.
WARNING
This appliance must be earthed
4.1 SAFETY EARTHING
The green-and-yellow wire of the mains cord The PS 285 employs professionally designed
must always be connected to the electrical audio input and output circuits which do not
installation safety earth or ground. It is require the disconnection of any safety earth for
essential for personal safety as well as for the avoidance of hum loops.
proper operation of the PS 285 and the other
connected stations. This wire is internally
connected to all exposed metal surfaces and
any rack framework into which this unit might
be mounted is assumed to be connected to
the same grounding circuit.
4.2 POWERING UP
Powering up procedure:
- Make sure that the red power switch on the left - Turn on the power with the red button. The red
side of the front panel is OFF. overload LED will light up for about 3 seconds, then
extinguishes. The yellow LEDS will go on, indicating
- Connect the power cord to the rear of the the station is standby.
station. - When a powered partyline is connected to the
intercom line input the green LED will go on,
- Plug the other end of the power cord into a indicating the station is active.
PROPERLY GROUNDED outlet.
See for further installation and operation the concerning
sections.
5.0 SET-UP 5.1 REMOTE CONTROLLED STANDBY MODE
When the main power supply has reached its limit, a This feature enables the user to activate or de-activate
PS 285 can be used to feed another group of user the PS 285 with the power on/off switch of the main
stations. Make sure the unit is placed correctly. power supply. The standby LED’s on the front panel
When, for example, 30 beltpacks are needed, they illuminate if there is no line power (from the main power
should be equally devided between the main power supply) available at the input connectors. The PS 285
supply and the PS 285. The booster should be placed will not supply power until the standby mode has been
in the middle of the chain of user stations. released by providing line power at the input.
Refer to page 10 for an example of a 2-channel
intercom network with a booster.
4 User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.

5. 6.0 FRONT PANEL CONTROLS
over
load
Pro series
PS 285
On Standby On Standby
Power
Supply
Booster
Power Intercom
CHANNEL A CHANNEL B
1 2 3 4
1 POWER ON/OFF switch 3 ON LED
Mains power push button for switching ON and OFF This LED illuminates if a partyline is connected to the
the internal power supply. intercom input and the unit supplies power to the
output.
2 OVERLOAD LED
This LED illuminates if the internal power supply has
shut off line power due to overload. 4 STANDBY LED
If the internal power supply is overloaded (too many This LED illuminates when no line power is detected at
user stations are connected or short-cicuit in the the input connector and no power is supplied to the
interconnecting cables), it activates a circuit-breaker output connector.
which immediately shuts off line power. This circuit-
breaker resets automatically 3 seconds after the
overload situition is terminated, restoring line power
automatically.
During short-circuit, the overload LED extinguishes
very shortly every 3 seconds.
This overload LED also comes on every time you
switch on the main power.
User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands. 5

6. 7.0 REAR PANEL CONTROLS & CONNECTORS
Type Serial Number B PUSH B A PUSH A AC Input voltage :
WARNING : THIS UNIT MUST BE EARTHED. 90 - 240 V
! HIGH VOLTAGE INSIDE
50 - 60 Hz
DISCONNECT MAINS INPUT BEFORE REMOVING COVER. USE 250V FUSES ONLY
Fuse :
Intercom
HOLLAND Intercom Line Intercom Line T 1250 mA
5 6 7 8
5 OUTPUT connector 7 FUSE
This XLR-3 supplies power to the user stations This fuse protects the PS 285 against severe internal
connected to the PS 285 when line power is damage, in case of malfunction in the power section.
supplied to the input connector. To remove the fuse the mains cord must be removed.
There is one connector for channel A and one
connector for channel B. It is most important to place the correct fuse in the
holder:
Pin assignments : mains voltage fuse
1. 0V / ground shield 90 – 240 VAC T 1250 mA
2. +30V power wire
3. audio wire Spare fuses will be found in the small packet supplied
with the unit.
6 INPUT connector
This XLR-3 is the sense input and should be 8 MAINS inlet
connected to the intercom line from the main IEC Mains connector. For correct wiring and
power supply. operation refer to section 4.0.
There is one connector for channel A and one
connector for channel B.
Pin assignments are like the output connector.
WARNING
Before you plug in the mains voltage, check if:
* The fuse is correct
6 User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.

7. 8.0 CABLING
For the PRO Series Intercom system the interconnecting
cables are of the shielded two-conductor microphone cable
type and the intercom line connectors are of the XLR-3
type. Audio and Call signals are on XLR pin 3, DC power is
on XLR pin 2. XLR pin 1 is connected to the shield of the
cable which functions as the common return for audio and
power.
Since the audio signal is transferred in an unbalanced
way, certain rules have to be obeyed when installing the
cables of an intercom network. This is to avoid earth loops
and to minimize power loss and the possible effect of
electromagnetic fields.
These rules are:
• Use high quality (multipair) cable. • Keep cables parallel as much as possible
For interconnecting user stations, power supplies When two (multi channel) units in a network are
and accessories in an ASL Intercom network, use connected by more than one cable, make sure that
high quality shielded two-conductor (minimum 2x these cables are parallel to each other over the whole
0.30 mm2) microphone cable only. distance between those units. When using multipair
In case of a multi channel intercom network, use cable, parallelism is ensured in the best possible way.
high quality microphone 'multipair' cable only, each
pair consisting of two conductors (minimum 2x 0.15 • Avoid closed loops.
mm2) with separate shield. Multipair cable should Always avoid that cables are making a loop. So-called
also have an overall shield. 'ring intercom' should not physically be cabled as a ring.
All cable routes should have a 'star' configuration, with
• Use flexible cables. the central earthing point (usually close to the power
Use flexible single and multipair microphone cable supply position) as the centre of the star.
instead of cable with solid cores, especially when the
cable is subjected to bending during operation or • Keep cables away from electromagnetic sources.
installation. Keep intercom cables away from high energy cables,
e.g. 110/220/380V mains power or dimmer controlled
• Separate cable screen to XLR pin 1. feeds for spotlights.
The screen of each separate microphone cable Intercom cables should cross high energy cables at an
and/or the screen of each single pair in a multipair angle of 90° only.
cable, should be connected to pin 1 of each XLR-3 Intercom cables should never be in the same trunking
connector. Do not connect this cable screen to the as energy cables.
metal housing of the connector or to metal wall
boxes (outlets). • Place power supplies in a central position.
See page 12 for Earthing Concept. In order to avoid unacceptable power losses, place the
power supplies as close as possible to where most
• Cable trunks, connection boxes and overall power consumption occurs or, in other words, most user
multipair cable screen to clean earth. stations are placed.
Metal cable trunks, metal connection boxes and
overall multipair cable screen should be inter- • Connect ASL power supply to a 'clean' mains outlet.
connected and, at one point (the 'central earthing The ASL power supply may be connected to the mains
point') in the intercom network only, be connected to power outlet to which other audio equipment is
a clean safety earth. connected. Avoid using mains outlets which also power
See page 12 for Earthing Concept. dimmer controlled lighting systems.
• Keep metal connection boxes and cable trunks In case of more complex installations, don't hesitate to
isolated from other metal parts. contact us. Please send us a block diagram of the
Metal housings for intercom cables and connectors planned network with a list of all user stations and their
should be mounted in such a way that they are positions, and we are happy to advise you on cabling
isolated from other metal cable and connector lay-out.
housings and from any other metal construction
parts.
See Party Line, Technical Concept
User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands. 7

8. 9.0 PARTY LINE, TECHNICAL CONCEPT 11.0 TECHNICAL SPECIFICATIONS PS 285
ASL's PRO Series offers a complete two way ('full POWER SUPPLY
duplex') communications system. mains voltage range 90 – 230 V 60Hz AC
Users of the system are connected via a 'party line'. DC ouput voltage +30 V +/- 5% DC
Master stations (with built-in power supply), beltpacks, ripple and noise < 11 mV rms
speaker stations and power supplies are max. output current 1.7 A continous, 3 A peak
interconnected via standard microphone cable. One circuit-breaker delay time 0.2 sec.
wire is used as an audio line, one as a power line and automatic reset time 3.0 sec.
the screen of the cable functions as earth/return.
Current drive is used for signal transfer. Each station DIMENSIONS AND WEIGHT
utilises a current amplifier to amplify the microphone width 19" (483mm)
signal and place it on the common audio line where, height 1U (44.5mm)
due to the constant line impedance (situated in the depth 150mm
power supply between XLR pin 3 and 1), a signal weight 1.60 Kg
voltage is developed which can be further amplified
and sent to headphones or loudspeakers.
GENERAL SPECIFICATIONS
This principle has three advantages: intercom line impedance 350 ohms (1kHz)
2.2 Kohms (DC)
- the use of a single audio line allows several intercom line audio level nom. –18 dBu
stations to talk and listen simultaneously. Max. +4 dBu
- due to the high bridging impedance offered by dynamic range 80 dB
each station, the number of stations 'on line' has call send signal +2.8 mA
no influence on the level of the communications call receive signal threshold +2.4 V DC
signal. supply voltage +30 V DC (12 V to 32 V)
- power and audio to the intercom stations use the
same cable.
Note: 0 dBu = 775 mV into open circuit.
The Call signal is also sent as a current on the audio ASL reserve the right to alter specifications without
line. It develops a DC potential over the line further notice.
impedance which will be sensed by each station and
interpreted as a Call signal.
10.0 GUARANTEE
This unit is warranted by ASL Intercom to the original
end-user purchaser against defects in workmanship
and materials in its manufacture for a period of one
year from the date of shipment to the end-user.
Faults arising from misuse, unauthorised modifications
or accidents are not covered by this warranty. If the
unit is faulty, it should be sent in its original packing to
the supplier or your local ASL dealer, with shipping
prepaid. A note must be included stating the faults
found and a copy of the original suppliers invoice.
THIS PRODUCT WAS DESIGNED, DEVELOPED
AND MANUFACTURED BY :
ASL-INTERCOM BV
UTRECHT, THE NETHERLANDS
http://www.asl-inter.com
email: info@asl-inter.com
8 User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.

9. Fuse
1,25A
L
Mains Switched mode power supply 1 1
earth 2 2
switch
ON 3 3
N
Power
control
circuit
User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.
2 1 2 1
3 3
9
Block diagram PS-285
(C) 2004 ASL-intercom BV

10. 10
PS 19 PS 19 PS 29 PS 19A PGM
PS 278
PS 285
AUX
A
B
IS 140
2-CHANNEL INTERCOM NETWORK WITH BOOSTER
User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands.

11. User Manual PS 285 / Issue 1 © 2004 ASL Intercom, Utrecht, The Netherlands. 11