Adastra A4-PLUS User manual

A4-PLUS
Rackmount Stereo Amplifier with Media Player
Item ref: 953.434UK
User Manual
Version 1.0
Caution: Please read this manual carefully before operating
Damage caused by misuse is not covered by the warranty

A4-PLUS User Manual
Introduction
Thank you for choosing the Adastra A4-PLUS rackmount dual stereo amplifier to power your public address system. This
amplifier is designed to offer high quality, reliable service for mobile and installed systems. Please read this manual fully
and follow the instructions to achieve the best results with your new purchase and to avoid damage through misuse.
SAFETY SYMBOL AND MESSAGE CONVENTIONS
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
AVIS
RISQUE DE CHOC ELECTRIQUE NE PAS
OUVRIR
This symbol indicates that dangerous voltage constituting a risk of electric shock is
present within this unit
This symbol indicates that there are important operating and maintenance instructions in
the literature accompanying this unit.
SAFETY NOTICE
1. Prior to use, read through this manual
2. Keep the manual in good condition
3. Pay attention to safety warnings
4. Observe all operating requirements
5. Do not use the device near water or wet areas
6. For cleaning, only use a lint-free, dry cloth
7. Install according to the specifications
8. Place away from heat sources or heating appliances
9. Use mains lead provided and avoid damage to cable or connectors
10. Unplug power from mains during stormy weather or if unused for long periods
11. In case of malfunction, water ingress or other damage, consult qualified service personnel
12. Do not place in damp areas or near liquids or moisture. Do not spill liquids on the housing
13. Please pay attention to warning symbols during transit and placement
14. Terminals marked with the symbol are HAZARDOUS LIVE and should only be connected by qualified personnel
15. Ensure that the apparatus is connected to a mains socket with a protective EARTH connection
16. Ensure correct operation of the mains switch
Warning
To prevent the risk of fire or electric shock, do not expose any components to rain or moisture.
If liquids are spilled on the casing, stop using immediately, allow unit to dry out and have checked by qualified personnel before
further use. Avoid impact, extreme pressure or heavy vibration to the case
No user serviceable parts inside –Do not open the case –refer all servicing to qualified service personnel.
Safety
•Check for correct mains voltage and condition of IEC lead before connecting to power outlet
•It is recommended to use speaker wire with a minimum current rating of 6A per output.
•Do not allow any foreign objects to enter the case or through the ventilation grilles
Placement
•Keep out of direct sunlight and away from heat sources
•Keep away from damp or dusty environments
•For rack-mounting, use the rack ears provided and ensure adequate support for the weight of the amplifier
•Ensure adequate air-flow and do not cover cooling vents
•Ensure adequate access to controls and connections
Cleaning
•Use a soft cloth with a neutral detergent to clean the casing as required
•Use a vacuum cleaner to clear ventilation grilles of any dust or debris build-ups
•Do not use strong solvents for cleaning the unit

A4-PLUS User Manual
Front panel
1.
Power on/off switch
12.
Channel 1 / 3 output level control
2.
SD card slot
13.
Channel 2 / 4 output level control
3.
Media player display
14.
USB port
4.
3.5mm stereo Aux input
15.
Media player control panel
5.
Aux input volume control
16.
Mic 1 input 6.3mm jack
6.
Media player volume control
17.
Mic 2 input 6.3mm jack
7.
Line 1 input volume control
18.
Mic 1 volume control
8.
Line 2 input volume control
19.
Mic 2 volume control
9.
Stereo input selector
20.
Talkover on/off button
10.
Bass EQ control
21.
Output Signal & Clip indicators
11.
Treble EQ control
Rear panel
22.
Ventilation grille (do not obstruct airflow)
28.
Line 1 input (L+R 6.3mm jack)
23.
FM antenna connection (F type)
29.
Line 1 input (L+R RCA)
24.
Line 2 input (L+R RCA)
30.
Line output Ch1+Ch2
25.
Line output Ch3+Ch4
31.
Channel 3 speaker output +/- 4mm posts
26.
Channel 1 speaker output +/- 4mm posts
32.
Channel 4 speaker output +/- 4mm posts
27.
Channel 2 speaker output +/- 4mm posts
33.
IEC mains inlet & fuse holder

A4-PLUS User Manual
Speaker connections
The A4-PLUS has 4 speaker output channels (Ch1, Ch2, Ch3, Ch4) which can be assigned as 2 independent
stereo zones –i.e. Left 1 + Right 2 outputs and Left 3 + Right 4 outputs.
When connecting speakers, connect “–” to the “–” output terminal(s) and “+” to the “+” output terminal(s)
Connect speakers with a combined impedance of no lower than 4Ω(4 Ohms) to each output channel.
•If the speakers are 8Ωimpedance, you can connect up to 2 speakers in parallel to each channel.
•If the speakers are 16Ωimpedance, you can connect up to 4 speakers in parallel to each channel.
Some example wiring diagrams are
shown opposite with speakers
connected in parallel.
The impedance of the load
measured in “Ohms” (Ω) will also
determine the power output.
The amplifier delivers its maximum
power output at the minimum
impedance rating (4Ω).
Higher impedances result in a lower
output.
•Note: Some speakers have 4Ωimpedance, in which case connect only 1 speaker to each channel.
The combined load on each output shares the power from the amplifier. If the amplifier is delivering 300W to
2 speakers connected in parallel with the same impedance, they must each be capable of handling 150W.
Input connections
The A4-PLUS has 2 mic inputs and 4 selectable stereo sources (one is the internal media player)
Connect wired microphone(s) to the Mic 1 and/or Mic 2 jack inputs (6.3mm) on the front panel (16, 17)
The volume level of these is controlled by the Mic 1 and Mic 2 volume controls (18, 19)
A smart phone, tablet or mp3 player can be connected to the Aux jack (3.5mm) on the front panel (4)
The volume level of this stereo input is controlled by the Aux volume control (5)
To hear this input through the speakers, “AUX” must be set on the input selector (9) of either stereo zone.
On the rear panel, there are 2 further stereo line inputs for connecting CD/DVD players, DVB/DAB tuners etc.
Line 1 input has a choice of Left + Right 6.3mm jack (28) or RCA inputs (29)
The volume level of this input is controlled by the Line 1 volume control (7)
To hear this input through the speakers, “LINE 1” must be set on the input selector (9) of either stereo zone.
Line 2 has Left + Right RCA inputs (24)
The volume level of this input is controlled by the Line 2 volume control (8)
To hear this input through the speakers, “LINE 2” must be set on the input selector (9) of either stereo zone.
The mix of mic/line inputs to Ch1+Ch2 can be fed onto further equipment via the RCA line output (30)
The mix of mic/line inputs to Ch3+Ch4 can be fed onto further equipment via the RCA line output (25)
For good reception of FM radio stations (if needed) in the media player, the A4-PLUS has an “F” connector on
the rear panel (23) which can be connected to an external FM antenna (aerial)
Connect the IEC power inlet (33) to the 230Vac mains supply, using the IEC lead provided.

A4-PLUS User Manual
Operation
When all connections to the amplifier are made, turn all rotary controls down and switch on the power (1) and
the media player display will illuminate.
Turn Bass and Treble controls (10, 11, 23, 24) to the 12 o’clock position (pointing straight up) and turn the
Ch1, Ch2, Ch3 and Ch4 rotary controls (12, 13, 25, 26) up part way for testing.
If a microphone is connected to one of the mic inputs (17, 18) gradually increase the volume control for that
channel (19,20) and speak into the mic until it is heard through the speakers.
Alternatively, play a signal into one of the aux or line inputs (4, 33, 34, 35) and ensure it is selected on the
input selector (9, 22) and turn up its volume control (5, 7, 8) until the signal is heard through the speakers.
The same test applies for the internal media player (see section below) by playing a track or radio station.
Select “MEDIA PLAYER” on the input selector (9, 22) and gradually increase the media player volume (6)
Turn up the Ch1, Ch2, Ch3 and Ch4 volume controls to the maximum required volume level and reduce the
channel volume control if necessary.
The output of each speaker channel is represented on the SIG and CLIP LEDs (14) and care should be taken
that the red CLIP LED is only lit momentarily during use. Anything longer than a short flash of this LED may
be indicating distortion or clipping of the output signal and the output channel volume control should be
turned down.
Any microphones connected should not be able to “hear” the speakers, which can cause feedback (squealing
or howling) and should not be pointed towards the speakers. If this still happens, turn down the volume for
that microphone and adjust Bass and/or Treble EQ controls to reduce the feedback.
If the TALKOVER feature (21) is switched on, speaking into the microphone will “override” any audio playback
from the selected stereo Aux, Line or Media input, which will be reduced in volume temporarily.
This allows voice announcements to be heard without interference from the line inputs or media player.
In addition to input and output volume controls, there are Bass and Treble EQ controls (10, 11, 23, 24) to
adjust the tone of the overall output of each pair of outputs. At the 12 o’clock position, these controls apply no
effect to the signal (no boost or cut).
Moving the Bass control clockwise boosts the low frequencies in the audio, whilst moving it anticlockwise will
cut these low frequencies.
Likewise, moving the Treble control clockwise boosts the high frequencies in the audio, whilst moving it
anticlockwise will cut these high frequencies.
Adjust these EQ controls to suit the type of audio signal or compensate for the room acoustics.
To avoid loud pops through the speakers, turn down the Ch1, Ch2, Ch3 and Ch4 volume controls before
powering down.

A4-PLUS User Manual
Media player
The A4-PLUS amplifier is equipped with a multi-functional media player for playback of audio files from USB or
SD media, FM radio stations or Bluetooth connection. Front panel controls are as described below.
MODE
Select between USB, SD, FM tuner & Bluetooth
REP
Repeat mode –Random, One, Folder and All

Previous track/FM station (hold for volume down)

Play/Pause (Auto-tune in FM mode)

Next track/FM station (hold for volume up)
EQ
Select preset - Bass/Pop/Rock/Jazz/Classical/Normal
USB/SD media playback
Insert USB or SD media containing mp3 tracks and playback should begin automatically.
The stored tracks should be standard mp3 audio format. If playback does not start, press MODE or 
The display will initially show the track number and then an elapsed time counter.
A USB or SD symbol will also be displayed to show which media is being used.
Ensure MEDIA PLAYER is selected on the output selector (9) and turn up the MEDIA volume control (6)
Tracks may be navigated by pressing for the previous track and for the next track.
Press and hold to reduce the media player volume or press and hold to increase the volume.
Playback can be paused and resumed by pressing 
Pressing REP sets the repeat mode: = random, = single track, = folder, = all tracks
Pressing EQ sets the preset:= bass, = pop, = rock, = jazz, = classical, = normal
FM Tuner
The FM tuner function operates in the same way as a standard FM radio and benefits from the connection of
an FM antenna to the rear panel ‘F’ type connector.
Press the media player MODE button until the display shows a frequency (e.g.”.MHz”)
If auto-tuning has already been performed, the display may show a channel (e.g. “”)
If no channels are tuned in, press the button to begin auto tuning, which scans available stations and
stores them as channels within the FM tuner. Pressing again will abort the auto-tuning.
To step through pre-set stations, press the or buttons…–––etc.
Press and hold to reduce the FM radio volume or press and hold to increase the volume.

A4-PLUS User Manual
Bluetooth
The Bluetooth function allows connection of a smart phone or tablet to the media player section for playback
of stored files or streamed digital audio. To enable this function, it will be necessary to pair the sending device
to the receiver as follows.
1. Press the media player MODE button until the display flashes “”
2. Open the Bluetooth settings menu on the smart phone or tablet (or other sending device)
3. Scan for Bluetooth devices and look for “A series” in the list of available devices
(ensure that the A4-PLUS is powered on, Bluetooth mode is selected and within reception range)
4. Select “A series” and the sending device should confirm that it is connected as an audio device.
5. Play audio from the sending device, ensuring that volume controls are not turned down/muted
6. Select MEDIA PLAYER input (9) and turn up the MEDIA volume control (6) to the required level.
The , and buttons will operate in Bluetooth as remote playback controls.
Holding the or buttons will adjust the output volume of the player.
If the sending device goes out of range, connection should automatically resume when back in range.
Likewise, if a different mode is selected, connection should resume when Bluetooth mode is re-selected.
If Bluetooth is disabled on the sending device or paired to a different receiver, it will be necessary to re-
connect the sending device to the A4-PLUS from step 2 above to re-establish a Bluetooth link.
Media player remote control
In addition to front panel controls, the media player can be operated via the supplied I.R. remote handset.
As supplied, the handset will have a plastic tab at the bottom to preserve battery charge before first usage.
Remove this tab by pulling away from the handset to engage the battery and activate the remote control.
If this needs to be replaced, the battery compartment can be slid out from the bottom to reveal the cell.
Replace the battery with a CR2025 button cell.
Point the top of the remote control towards the media player display and operate in line of sight.
Some of the controls on the remote handset mirror those on the front panel and are described below.
Media player power on/standby button
Repeat mode –select Random, One, Folder or All tracks
MODE
Select USB, SD, FM tuner or Bluetooth mode
CH- / CH+
Select FM radio station
EQ
Select preset EQ –Bass, Pop, Rock, Jazz, Classical or Normal
/ 
Previous or Next track select

Play / Pause track (auto-tune in FM tuner mode)
/ 
Adjust media player volume down or up
0 - 9
Direct track or channel access –key in number

A4-PLUS User Manual
Specifications
Power supply
230Vac, 50Hz (IEC)
Power consumption max.
540W
Fuse
F6.3A, 250V
Output power rms @ 4 Ohms
4 x 300W
Output power rms @ 8 Ohms
4 x 150W
Amplifier: construction
Class D
Frequency response
20Hz - 20kHz ±0.5dB
Microphone inputs
2 x 6.3mm jack (mono)
Line inputs
Line 1: L+R (6.3mm jack/RCA), Line 2: L+R (RCA), Aux (3.5mm stereo)
Input sensitivity: line
0.775Vrms
Input sensitivity: aux
0.480Vrms
Input impedance
20k Ohms (balanced), 10k Ohms (unbalanced)
Audio source
USB/SD mp3 playback, FM tuner, BT receiver
Input controls
Aux, Media, Line1, Line2, Mic1, Mic2, Talkover
Line output
4 x RCA
Speaker outputs
4mm binding posts (4 channels)
Antenna connection
F type (FM tuner)
Output controls
2 x Source select, 2 x Bass, 2 x Treble, Ch1, Ch2, Ch3, Ch4
Dynamic range
92dB
THD +N
<0.1%
Protection
Thermal, over-current, over-voltage, short-circuit
Dimensions
482 x 260 x 88mm
Weight
7.13kg
Troubleshooting
No power LED on control panel
Ensure IEC lead is in good condition and connected properly
Ensure POWER switch is on and check mains inlet fuse
Power light and output LEDs lighting
but no output
Check speaker output terminals are connected correctly
Check speakers are working (test on another amp if available)
Check memory device is connected properly (remove and re-insert)
Check file types –standard mp3 digital audio files required
Check memory device works on a PC or Mac for standard playback
Bluetooth cannot connect
Ensure that Bluetooth is enabled on sending device
Ensure that the sending device is within Bluetooth range (5-10m)
Check that the device is connecting to “A series”
No audio from Bluetooth device
Ensure that volume controls are not turned down on sending device
Check volume and Play/Pause buttons on media player
Output too loud or distorted
Reduce MIC, LINE IN, USB/SD and/or MASTER level
Ensure Hi-Z line level input(s) not connected to a Mic input
Output too quiet or inaudible
Increase MIC, LINE IN, USB/SD and/or MASTER level
Check for quiet recording of media files on USB
Check VOX override is not unintentionally suppressing audio playback
Feedback from microphone
Face microphone away from speakers and monitors and reduce level
Amplifier overheating
Ensure cooling vents are clear from debris and dust
Ensure that the load impedance on any output channel is no less than 4Ω
Disposal: The “Crossed Wheelie Bin” symbol on the product means that the product is classed as Electrical or
Electronic equipment and should not be disposed with other household or commercial waste
at the end of its useful life. The goods must be disposed of according to your local council guidelines.
Hereby, AVSL Group Ltd. declares that the radio equipment type 953.434UK is in compliance with Directive 2014/53/EU
The full text of the EU declaration of conformity is available at the following internet address:
http://www.avsl.com/assets/exportdoc/9/5/953434UK%20CE.pdf
Errors and omissions excepted. Copyright© 2022.
AVSL Group Ltd. Unit 2-4 Bridgewater Park, Taylor Rd. Manchester. M41 7JQ
AVSL (EUROPE) Ltd, Unit 3D North Point House, North Point Business Park, New Mallow Road, Cork, Ireland

EU Declaration of Conformity
AVSL Group Limited, Declare that the product:
953.434UK A4 PLUS Dual Stereo Amp 4 x 300W
Has been manufactured in conformity with the following standards:
EMC Directive: 2014/30/EU
Standard Date A1 A2 A3 A11 A12 A13
EN 55032 2015
EN 55035 2017
EN 61000-3-2 2014
EN 61000-3-3 2013
LVD Directive: 2014/35/EU
EN 62368-1 2014 2017
EN 62479 2010
RED Directive: 2014/53/EU
EN 300 328 V2.1.1 2016
EN 301 489-1 V2.2.1 2019
EN 301 489-17 V3.2.0
2017
EN 303 345 V1.1.7 2017
RoHS Directive: 2011/65/EU
EN 62321 2009
Date: 07/12/22
Authorised by: Chris Walsh
Position: Compliance Manager
Authorised Signature:

UK Declaration of Conformity
AVSL Group Limited, Declare that the product:
953.434UK A4 PLUS Dual Stereo Amp 4 x 300W
Has been manufactured in conformity with the following standards:
Electromagnetic Compatibility Regulations 2016
Standard Date A1 A2 A3 A11 A12 A13
BS EN 55032 2015
BS EN 55035 2017
BS EN 61000-3-2 2014
BS EN 61000-3-3 2013
BS
BS
Electrical Equipment (Safety) Regulations 2016
BS EN 62368-1 2014 2017
BS EN 62479 2010
BS
BS
BS
BS
Radio Equipment Regulations 2017
BS EN 300 328 V2.1.1 2016
BS
EN 301 489-1 V2.2.1
2019
BS
EN 301 489-17 V3.2.0
2017
BS EN 303 345 V1.1.7 2017
BS
BS
The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment Regulations 2012
BS EN 62321 2009
Date: 07/12/22
Authorised by: Chris Walsh
Position: Compliance Manager
Authorised Signature: