CH A1.5 User manual

A1.5 Two-channel Power Amplifier
User Manual

Dear Valued Customer,
e are honored that you chose the A1.5 Power Amplifier for your audio system. Our team devoted every effort to design and
manufacture this highest-quality versatile and future-proof product and is proud to present it to you. e wish you hours of
enjoyment from your music collection with the A1.5 Power Amplifier installed in your system.
Before you embark on your musical journey, we kindly request your special attention regarding the information contained in this
manual. The A1.5, as you will discover in the following pages, is a Swiss precision product designed for ultimate performance and
flexibility. However, reaching sonic excellence from your audio system requires your unit to be set up and operated correctly and
this what this manual is all about. If you have any questions or require assistance, please don't hesitate to contact your authorized
dealer.
e hope you will enjoy your A1.5 for many years to come.
The Concert has just begun...
Cossy F.
Heeb T.

Table of contents
1 Product highlights............................................................................................................................................................... 7
1.1 Unmatched flexibility................................................................................................................................................. 8
1.1.1 Operation modes............................................................................................................................................... 8
1.1.2 Feedback control............................................................................................................................................... 9
1.1.3 Gain control...................................................................................................................................................... 9
1.1.4 ExactBias.......................................................................................................................................................... 9
1.2 Advanced monitoring circuit...................................................................................................................................... 10
1.2.1 Power monitoring............................................................................................................................................ 10
1.2.2 Temperature monitoring.................................................................................................................................. 10
1.3 Mechanical construction............................................................................................................................................ 10
1.4 Modular architecture and slot-in boards..................................................................................................................... 10
1.4.1 Monaural analog inputs: ANALOG_IN board...................................................................................................... 11
1.4.2 Firmware update and control: CONTROL board................................................................................................... 11
1.5 Power supply........................................................................................................................................................... 11
2 Before use........................................................................................................................................................................ 12
2.1 Package content....................................................................................................................................................... 12
2.2 Safety notice............................................................................................................................................................ 13
2.3 Mains supply............................................................................................................................................................ 13
2.4 Transport and packaging.......................................................................................................................................... 14
2.5 Cleaning your unit.................................................................................................................................................... 14
2.6 Maintenance and service........................................................................................................................................... 14
3 Installation....................................................................................................................................................................... 15
3.1 Unpacking............................................................................................................................................................... 15
3.2 Unit positioning........................................................................................................................................................ 15
3.3 Connections.............................................................................................................................................................. 16
3.3.1 CONTROL board............................................................................................................................................... 18
3.3.2 ANALOG_IN board........................................................................................................................................... 19
3.4 Power cord receptacle and voltage selection............................................................................................................... 19
3.5 Amplifier modes....................................................................................................................................................... 20
3.5.1 Stereo mode.................................................................................................................................................... 20
3.5.2 Bridge mode................................................................................................................................................... 20
3.5.3 Monaural mode............................................................................................................................................... 21
3.5.4 Passive bi-amplification mode........................................................................................................................... 21
3.5.5 Active bi-amplification mode............................................................................................................................ 22
3.5.6 Daisy-chain mode............................................................................................................................................ 22
4 Operation......................................................................................................................................................................... 24
4.1 Front panel controls.................................................................................................................................................. 24
4.1.1 Front panel..................................................................................................................................................... 24
4.1.2 Front face pushbuttons..................................................................................................................................... 24
4.2 Operating modes...................................................................................................................................................... 25
4.2.1 Normal mode.................................................................................................................................................. 25
4.2.2 Shortcuts mode................................................................................................................................................ 27
4.2.3 Menu mode..................................................................................................................................................... 29
4.3 Configuration........................................................................................................................................................... 32
4.3.1 A1.5 configuration menu items......................................................................................................................... 32
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4.3.1.1 AUDIO SETTINGS..................................................................................................................................... 32
4.3.1.2 DISPLAY SETTINGS................................................................................................................................... 33
4.3.1.3 SHORTCUTS............................................................................................................................................ 34
4.3.1.4 FACTORY SETTINGS.................................................................................................................................. 35
4.3.1.5 INSTALLED OPTIONS................................................................................................................................ 36
4.3.1.6 NET ORK............................................................................................................................................... 37
5 Firmware update.............................................................................................................................................................. 38
5.1 Preparing the USB flash-drive................................................................................................................................... 38
5.2 Updating the unit's firmware.................................................................................................................................... 38
5.3 Emergency firmware update procedure...................................................................................................................... 39
6 Troubleshooting................................................................................................................................................................ 40
7 Specifications.................................................................................................................................................................... 41
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1 Product highlights
CH products are meticulously designed and manufactured in Switzerland by CH Precision Sàrl. Our engineers put together all their
know-how, expertise and ingeniousness to bring you the A1.5, a top performances future-proof modular 2-channel power
amplifier with Ethernet control capabilities and USB flash-drive firmware upgradability. Like all CH Precision products, the A1.5 is
highly versatile: 5 configuration are available with the A1.5: stereo mode requiring a single A1.5 and monaural, bridge mode,
active and passive bi-amplification modes requiring a pair of power amplifiers.
For increased flexibility, the A1.5 also provides two unique features: the global versus local feedback ratio and gain adjustments.
The amount of global feedback in the amplifying loop of each channel can be adjusted to best match virtually every loudspeaker
on the market. The amplifier gain can also be adjusted over a 24 dB range in 0.5 dB steps. This also greatly helps in matching the
output level of the preamplifier, the efficiency of the connected loudspeakers and the listening room. Three standard input are
available (balanced XLR, single-ended RCA and BNC). Unbalanced inputs can be configured as high impedance inputs, or a 300 Ω
load can be engaged. A pass-through XLR line-level output is also provided for daisy-chaining multiple CH amplifiers.
A1.5 main components
Rev 1.0 A1.5 User Manual 7

(1) Output coil for HF immunity
(2) Custom Argento Audio speaker terminals
(3) Monaural analog input boards (each A1.5 can be equipped with 1 or 2 such boards)
(4) Standby fuse
(5) Mains voltage selector
(6) Mains power switch
(7) Mains filter
(8) IEC C20 power cord receptacle
(9) Power fuse
(10) USB (firmware update) and ethernet RJ-45 (control) board
(11) Adjustment shafts
(12) Power supply regulation boards
(13) Heatsink-mounted monaural amplifier boards
(14) Heatsink-mounted rectifying diode bridges
(15) User interface buttons
(16) Custom rectifying capacitors
(17) Main analog star-ground oxygen-free copper plate
(18) Custom standby transformer (ensures green mode Standby)
(19) AMOLED display (on front panel)
(20) Custom high power transformer
1.1 Unmatched flexibility
The A1.5 offers unmatched system integration features. Not only does it provide multiple modes of operation (stereo, monaural,
bridge and active or passive bi-amplification) but it also provides adjustments to match speaker impedance and sensitivity through
feedback and gain controls. The operating modes are user-selectable either from the A1.5 amplifier's front panel or from the CH
Control app running on a tablet. In addition, multiple CH amplifiers can be daisy-chained for ultimate performance in multi-
amplification systems.
1.1.1 Operation modes
The A1.5 integrates two channels of amplification and can be fitted with a single or two input boards. hen fitted with a single
input board, two power amplifier units are required (one per channel) and the pair provides the following modes of operation:
•Bridge mode: In this mode, each A1.5 operates as a very high power mono amplifier and can deliver up to 550 atts
under 8 Ohms. Bridge mode is optimal for high impedance speakers in large rooms, requiring large voltage swings.
•Monaural mode: In this mode, the entire power supply is dedicated to a single amplification channel and each A1.5 unit
can deliver up to 700 atts under 1 Ohm. It is optimal for low impedance speakers, requiring large amount of current.
•Passive bi-amplification mode: Used with loudspeakers fitted with multiples sets of terminals. In this mode, each A1.5
operates its two channels of amplification in parallel, fed from the same input signal. Each channel drives a different set
of loudspeaker terminals. Feedback ratio and gain can be adjusted independently for each channel to best match the
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individual speaker sections. In Passive Bi-Amplification mode, each channel can deliver 150 atts under 8 Ohms.
By adding a second input board, the A1.5 provides the following additional operating modes:
•Stereo mode: In stereo mode, each amplification stage is driven by its dedicated input board and the amplifier operates
as a standard stereo power amplifier. Feedback and gain settings are replicated on both channels of amplification and
the A1.5 can deliver up to 2x 150 atts under 8 Ohms. It is the configuration used when a single A1.5 drives a pair of
speakers.
•Active bi-amplification mode: As per stereo mode, active bi-amp mode links each amplification stage to its dedicated
input board. Feedback and gain can however be adjusted individually for each channel in order to best match the
requirements of each driver. An active external crossover, usually fitted between the preamplifier (such as the CH
Precision's L1) and the A1.5, is generally used to split the signal into different frequency bands. In the Active Bi-
Amplification mode, each A1.5 can deliver up to 2x 150 atts under 8 Ohms.
1.1.2 Feedback control
One of CH range of power amplifier's most unique feature is its user controllable feedback. This feature provides control over the
ratio between global and local feedback applied in the A1.5's amplification stage. Global feedback takes a portion of the output
signal after the power stage and feeds it back to the input of the amplifier. This ensures a very low output impedance and low
distortion figures. Local feedback, on the other hand, does not include the output stage and lets the latter operate in open loop
mode. This favors small signal details and timing. As a rule of thumb, a higher ratio of global feedback is preferred for grip and
control in the low frequencies whereas a lower ratio is preferred for speed and details in the high frequencies. This rule is however
not absolute as each speaker and crossover are different and we highly recommend to experiment to find the best match with the
connected loudspeakers, especially if the A1.5 is driving a complete full bandwidth loudspeaker. In multi-amplification systems,
different feedback settings are commonly used for the various loudspeaker sections opening a whole new level of performance.
e recommend to start with pure local feedback and increase the global feedback until the bass are tight enough to your personal
taste. Feedback settings can be adjusted on the fly from the A1.5's front panel or from the CH Control app.
1.1. Gain control
The A1.5 provides an integrated gain control with a 24 dB range in 0.5 dB steps. This gain control allows an optimal matching of
the speaker sensitivity, room size, and preamplifier output level. In multi-amplification systems it can be used to match the
sensitivity of the individual speaker sections. Gain can be adjusted on the fly from the A1.5's front panel or from the CH Control
app.
1.1.4 ExactBias
The A1.5 features an advanced bias control circuitry called ExactBias that not only Counteracts the effect of slow temperature
variations, but also accurately takes into account all the dynamic aspects induced by transients in the musical content.
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1.2 Advanced monitoring circuit
1.2.1 Power monitoring
Each power amplifier board is equipped with a DSP that monitors the instantaneous output voltage and current delivered to the
loudspeaker. Both values are sampled at around 100 kHz, ensuring peak values are properly detected. DSP monitoring has
several purposes: to give the user a feedback on the peak power delivered to the loudspeakers and to detect and act in case of a
malfunction such as a short-circuit or amplifier damage.
1.2.2 Temperature monitoring
The DSPs also monitor the temperature of both the power transistors and the heatsinks. If the temperature gets excessive, the A1.5
will protect itself by turning itself off.
1. Mechanical construction
The A1.5 power amplifier is assembled from high-quality aluminum and steel elements with no visible screws on the front, top and
side panels. The front panel, base, side panels and top cover are machined from aluminum. The power supply is based on a fully
shielded 1'700 VA toroidal transformer and ultra low ESR rectifying capacitors sitting in the central position of the unit. The area
where the air flows to cool down the amplifier is hermetically sealed from the rest of the A1.5, ensuring the electronic circuitry is
protected from gradually gathering dust. Pin assembly of all chassis elements provides smooth joints between elements while
screws every 6cm ensures protection against electromagnetic interference. First class mechanical and chemical surface treatments
provide the luxury finish of the A1.5.
Four steel feet support the unit. Each foot ends with a elastomer ring to sit on delicate surfaces but is also equipped with a height
adjustable steel spike to fine tune the positioning of the unit. Horizontal adjustment is done with the provided screwdriver through
the four adjustment shafts accessible from the top of the unit. In addition to providing convenient horizontal adjustment from the
top of the unit, the shafts also serve as vibration evacuation channels for stacked units.
Special shaft covers (stacking covers) are provided to interface with the spikes of a stack of units. Any vibration from the upper
unit is transmitted by the shaft cover to the shaft of the lower unit and from there to the lower unit's feet or spikes, forming a
privileged path for vibrations evacuation. Support discs are provided and should be placed between the spike of the bottom unit
and the piece of furniture holding the equipment.
1.4 Modular architecture and slot-in boards
The A1.5 benefits from a fully modular architecture. It features separated sections for power rails, analog and digital power
supplies, front panel, signal routing and central host processor, monaural analog input boards and single channel amplification
boards. This modular architecture combined with the USB plug for firmware update allows for easy servicing and upgrade should
one section become faulty or obsolete.
The slot-in boards section consists of a vertically mounted backplane board with optional boards plugged into it. Optional boards
provide audio functionality and connectivity to other equipment.
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1.4.1 Monaural analog inputs: ANALOG_IN board
The ANALOG_IN board features a user-selectable mono analog inputs on three different connectors: single-ended RCA, single-
ended BNC and balanced XLR. Both the RCA and BNC inputs can be configured for high-impedance or 300 Ω load. In addition to
its inputs, the ANALOG_IN board includes an XLR output providing a pass-through of the input signal used to daisy chain
amplifiers.
1.4.2 Firmware update and control: CONTROL board
The CONTROL board is factory fitted to each A1.5. It features a USB port for software updates (using the provided USB flash-drive)
and an Ethernet port for remote-controlling the unit over a standard Ethernet network.
1.5 Power supply
The power supply of the A1.5 is a linear supply with multiple independent local regulations. It is based on an overspecified
magnetically shielded toroidal 1'700 VA mains transformer. A second toroidal transformer is used as standby transformer to
ensure green standby mode, meeting the latest energy saving regulations. Both transformers have static shields between primary
and secondary windings. They are mounted on a separate metal plate which is isolated from the main base plate by silent blocks.
Two 82'000μF electrolytic capacitors are used as reservoirs and filters to the main power supply. These capacitors exhibit
exceptionally low ESR, huge current capability, very high speed and high capacitance, providing instantaneous response to current
draw from the output stage.
Discrete (power-transistor and op-amp based) ultra low-noise regulators are used throughout the power supply system to ensure
the purest low noise DC feed possible to the different sections. The input stages of the power section are also fully regulated to
avoid any coupling distortion. A thick copper plate acts as signal ground star connection.
Input AC voltage to the power supply can be set to 100V, 115V or 230V AC to match your local mains voltage.
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2 Before use
Please read this manual carefully before making connections or operating your A1.5. After reading this manual, please store it in
an accessible place for future reference. If after reading this manual you feel unsure about how to make connections or how to
operate the unit, please contact your authorized dealer for assistance.
2.1 Package content
Please make sure that the package content is complete. If not, please contact your authorized dealer. Your package should
contain:
•Your A1.5 power amplifier with one or two input boards depending on what you ordered
•An IEC C19 power cord
•Four adjustment steel spikes
•A suction cup (used to unscrew the top covers)
•An accessory box containing:
◦a spike adjustment screwdriver
◦a Torx 10 screwdriver
◦four stacking covers
◦a USB flash-drive containing the latest CH Precision firmware.
◦a set of four CH Support Discs
Please store the packaging for future use. Check your A1.5 for any apparent damage. In case of a damage, immediately contact
your authorized dealer. If your A1.5 is cold due to transport, please let it warm up to room temperature before powering it up.
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2.2 Safety notice
Make sure to observe the following rules:
•Install your A1.5 power amplifier on a stable and sturdy base
•Do not install your A1.5 power amplifier near water
•Always handle the unit with care. The A1.5 power amplifier is very heavy, always have someone to help you when
moving it around
•Do not expose the unit to any kind of liquid
•Do not install in direct sunlight or near any heat sources such as radiators
•Do not install in a confined space and make sure sufficient air can flow around the unit, including under the unit.
•Never install your A1.5 power amplifier directly on a carpet or any soft material that could block off the ventilation
openings at the bottom of the unit
•Do not operate under high ambient temperature (>40°C) or with extremely high humidity
•Only use options and accessories specified or recommended by CH Precision
•Do not open the unit nor try to service it by yourself. Always refer to a qualified technician for service, maintenance or
upgrades. Failure to do so will void the unit's warranty
2. Mains supply
Make sure to use a 3 terminals (phase, neutral and earth) power cord with ground conductor. Make sure that the mains voltage
selection of the unit matches the mains voltage in your location.
Make sure your A1.5 power amplifier is disconnected from the AC wall power in the following cases:
•hen making connections (it is also recommended to disconnect the rest of the system from AC wall power)
•hen cleaning the unit
•During thunderstorms
•hen unused for a long period of time
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2.4 Transport and packaging
The A1.5 power amplifier must always be stored in its original packaging for transportation. Doing so will ensure the optimal level
of protection of your unit. Keep all the packaging material in a dry and clean place.
Besides, we recommend to remove the adjustment spikes and to put them into the A1.5 box (four holes in the bottom piece of
foam) for transportation. Vibrations during transport may cause the adjustment spikes to move from their fully retracted position
and you run the risk of scratching your rack if the spikes are not fully retracted when installing the unit.
2.5 Cleaning your unit
Use a soft, dry towel or cloth for cleaning. Never use any solvent or liquids as they may damage the surface treatment or
penetrate inside the unit.
2.6 Maintenance and service
The A1.5 power amplifier contains no user serviceable parts. Do not try to open, modify or attempt any repair on your A1.5. This
will void any warranty. Your A1.5 power amplifier must be serviced by a qualified technician in any of the following cases:
•The unit is not functioning properly
•The mains cable or the power cord receptacle is damaged
•The unit has been dropped to the floor or presents external damage
•The A1.5 power amplifier has been exposed to liquids (such as rain) or unknown substances
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Installation
.1 Unpacking
Unpack the A1.5 power amplifier and store the packaging for future transportation. Be careful when lifting the A1.5 as the unit is
very heavy. Always get someone to help you. hen unpacking and installing the A1.5, please remove any rings or watches you
may wear to prevent any damage to the high quality surface treatments.
.2 Unit positioning
e recommend to locate the A1.5 power amplifier close to the loudspeaker(s) it drives and connect it by using short loudspeaker
cables.
For best transmission and immunity to external noise, we recommend to connect the A1.5 input to the upstream unit (preamplifier)
using balanced XLR cables.
hen delivered from factory, the A1.5 amplifier's four feet sit on elastomer rings, ensuring both scratch-protection for the base on
which the unit sits as well as safe anti-slipping unit positioning. However, a more advanced vibration-channeling mechanical
coupling can be implemented thanks to the steel spikes and the polymer support discs provided with the A1.5. To use this optimal
coupling, simply go through the following steps:
1. Place the A1.5 unit on a stable base in its approximate final position, for instance in your preferred audio rack. Make
sure cool air is able to freely flow around the unit.
2. Gently lift the unit's corners and insert a support disc under each foot. The foot's elastomer ring should disappear in the
support disc's groove when properly placed. Carefully check all four feet perfectly fit in each support disc before pursuing
any further. The unit should stably rest on its feet at that point.
3. Unscrew the four top covers from the A1.5's shafts using the provided suction cup.
4. Insert the adjustment spikes into the unit's four shafts.
5. Using the provided screwdriver, gently screw each adjustment spike clockwise until some resistance is felt (just before the
spike starts lifting the unit).
6. Then screw clockwise each spike by the same amount (for example two full turns).
7. If the base is flat, the unit should be stable and horizontal. If not, correct the unit's stability and horizontality by
adjusting the required spikes.
8. If no other CH Precision unit is to be stacked on top of the A1.5, screw the four top covers back. Otherwise, screw the four
polymer stacking covers instead, and gently lay down the unit to be stacked on top of the A1.5. Be very careful that both
units are perfectly aligned in order not to scratch the A1.5's top plate with the other unit's feet. Repeat steps 3 to 8 on
the upper unit.
Rev 1.0 A1.5 User Manual 15

Adjustment shafts, feet and spikes
(1) Adjustment shafts. Insert adjustment spikes and use screwdriver to secure and adjust individual feet spikes
(2) Feet
(3) Adjustment spike heads (when inserted into adjustment shafts)
(4) Adjustment spike
Never stack any component other than CH's on your A1.5. Never use the aluminum shaft covers (top covers) when another CH
component is to be stacked on top of your A1.5.
Shaft covers (left: stacking cover, right: top cover)
. Connections
This section provides information about how to connect the A1.5 power amplifier to your system. As the A1.5 is a modular design
with different optional boards, the description applies to the example configuration presented below. For details about how to
integrate your A1.5(s) in a specific setup, please refer to the Amplifier modes section of this user manual. If you feel unsure with
the connections to be applied to your specific configuration, please contact your authorized dealer for assistance.
The example configuration is a stereo-ready (2 input boards) power amplifier. Your amplifier could only contain a single input
board if your ordered a pair of amplifiers.
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A1.5 rear panel connections
(1) Argento Audio right negative speaker terminal
(2) Argento Audio right positive (or bridge mono positive) speaker terminal
(3) Ethernet RJ-45 port for command interface [CONTROL board]
(4) USB port for software upgrades. [CONTROL board]
(5) Analog ground connectors. The bottom one can be connected to digital ground (Earth) using the provided jumper
(6) Earth connector. Internally connected to digital ground
(7) BNC single-ended analog input for right channel [Right ANALOG_IN board]
(8) RCA single-ended analog input for right channel [Right ANALOG_IN board]
(9) XLR balanced analog output (pass-through for amplifier chaining) for right channel [Right ANALOG_IN board]
(10) XLR balanced analog input for right channel [Right ANALOG_IN board]
(11) XLR balanced analog input for left channel [Left ANALOG_IN board]
(12) XLR balanced analog output (pass-through fo amplifier chaining) for left channel [Left ANALOG_IN board]
(13) RCA single-ended analog input for left channel [Left ANALOG_IN board]
(14) BNC single-ended analog input for left channel [Left ANALOG_IN board]
(15) Argento Audio left positive (or bridge mono negative) speaker terminal
(16) Argento Audio left negative speaker terminal
(17) Standby fuse
(18) Mains voltage selector
(19) Mains power switch
(20) IEC C20 power cord receptacle
(21) High current fuse for main high power transformer
Rev 1.0 A1.5 User Manual 17

. .1 CONTROL board
The CONTROL board is factory installed into the A1.5. It provides a USB port for software updates and an Ethernet port for remote-
controlling the unit over an Ethernet network. The following drawing shows the layout of the back panel of the CONTROL board:
CONTROL board back panel layout
The USB port on the CONTROL board is dedicated to the firmware update of the A1.5 unit. Do not use it for any other purpose. For
more information on unit firmware update, please refer to the corresponding section of this manual.
The Ethernet port on the CONTROL board is dedicated to network based control of the unit. Connect the A1.5 Ethernet port to an
off-the-shelf Ethernet router equipped with iFi access. Connect an Android tablet to the iFi network of the router. Install the CH
Control app on the Android tablet, freely available from the Google Play Store. Once installed, run the app. The app gives you
access to all the settings of the A1.5.
. .2 ANALOG_IN board
The ANALOG_IN board features three user-selectable mono analog inputs on three types of connectors: single-ended RCA, single-
ended BNC and balanced XLR. Both the RCA and BNC inputs can be configured for high-impedance or 300 Ω load. In addition to
their inputs, ANALOG_IN boards include an XLR output providing a pass-through of the XLR input signal. This output can be used to
daisy-chain multiple A1.5s or other CH amplifiers in multi-amplification systems for ultimate performance. Balanced connections
are recommended for optimal performance. The analog stage design is fully discrete and balanced. The following drawing shows
the layout of the connectors on the ANALOG_IN boards:
ANALOG_IN panel layout
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.4 Power cord receptacle and voltage selection
Make sure that the voltage selection is set to the correct value with respect to the AC voltage in your location. Connect the IEC C19
power cord to the IEC C20 power cord receptacle and plug the power plug to an AC wall outlet only after all other connections were
made.
If third-party power cords are used, make sure that the socket mating with the A1.5 is fully inserted and not able to move and
create intermittent contacts due to its own weight.
.5 Amplifier modes
This section describes the most standard setups in which one or multiple A1.5 amplifiers can be integrated into.
.5.1 Stereo mode
A single A1.5 equipped with two analog input boards can be used as a stereo power amplifier. This is the simplest configuration
that already allows to enjoy the unique sound of the A1.5 amplifier. The picture below shows how the stereo mode should be
wired.
Stereo mode
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.5.2 Bridge mode
A pair of A1.5 amplifier, each equipped with a single analog input board can be used as a pair of high power monoblock amplifiers
with high voltage swing. This configuration should be used when low efficiency high impedance loudspeakers are used in large
rooms to achieve higher sound level than with a single stereo A1.5. This configuration also exhibits a better signal-to-noise ratio.
The picture below shows how the bridge mode should be wired.
Bridge mode
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