CH A1.5 Manual de usuario
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
6 A1.5 User Manual Rev 1.0
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
8 A1.5 User Manual Rev 1.0
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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