CH A1 User manual

A1 Power Amplifier
User Manual

Dear Client,
We are honored that you have chosen the CH A1 Power Amplifier. ur team has put all his efforts into designing and
manufacturing this top quality versatile and future-proof product and is proud to present it to you. We hope your A1 will bring you
uncountable hours of emotion from your musical collection.
But before starting your musical journey, we kindly ask you to pay attention to the information contained in this manual. The A1,
as you will discover in the following pages, is a Swiss precision product designed for ultimate performance and flexibility. However,
reaching sonic excellence requires your unit to be setup 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.
We hope you will enjoy your A1 amplifier for many years.
The Concert has just begun...
Cossy F.
Heeb T.

Table of contents
1 Technical highlights.............................................................................................................................................................. 7
1.1 Unmatched flexibility.................................................................................................................................................. 8
1.1.1 peration modes................................................................................................................................................ 8
1.1.2 Feedback control................................................................................................................................................ 9
1.1.3 Gain control....................................................................................................................................................... 9
1.1.4 Bias adjustment.................................................................................................................................................. 9
1.2 Advanced monitoring circuit......................................................................................................................................... 9
1.2.1 Power monitoring............................................................................................................................................... 9
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: ANAL G_IN board....................................................................................................... 11
1.4.2 Firmware update and control: C NTR L board.................................................................................................... 11
1.5 Power supply............................................................................................................................................................ 11
2 Before use......................................................................................................................................................................... 12
2.1 Package content........................................................................................................................................................ 12
2.2 Safety notice............................................................................................................................................................. 12
2.3 User manual............................................................................................................................................................. 13
2.4 Mains supply............................................................................................................................................................. 13
2.5 Transport and packaging............................................................................................................................................ 13
2.6 Cleaning................................................................................................................................................................... 14
2.7 Maintenance and service............................................................................................................................................ 14
3 Installation........................................................................................................................................................................ 15
3.1 Unpacking................................................................................................................................................................ 15
3.1.1 Removing the security screws............................................................................................................................ 15
3.2 Unit positioning......................................................................................................................................................... 15
3.3 Connections............................................................................................................................................................... 17
3.3.1 C NTR L board................................................................................................................................................ 18
3.3.1.1 USB port.................................................................................................................................................. 18
3.3.1.2 Ethernet port........................................................................................................................................... 19
3.3.2 ANAL G_IN boards.......................................................................................................................................... 19
3.3.3 Power cord receptacle and voltage selection....................................................................................................... 19
3.4 Amplifier modes........................................................................................................................................................ 19
3.4.1 Stereo mode..................................................................................................................................................... 19
3.4.2 Bridge mode.................................................................................................................................................... 20
3.4.3 Monaural mode................................................................................................................................................ 20
3.4.4 Passive bi-amplification mode............................................................................................................................ 21
3.4.5 Active bi-amplification mode............................................................................................................................. 21
3.4.6 Chained mode.................................................................................................................................................. 22
4 peration.......................................................................................................................................................................... 23
4.1 Front panel controls................................................................................................................................................... 23
4.1.1 Front panel...................................................................................................................................................... 23
4.1.2 Front face push-buttons..................................................................................................................................... 23
4.2 perating modes....................................................................................................................................................... 24
4.2.1 Normal mode................................................................................................................................................... 24
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4.2.2 Shortcuts.......................................................................................................................................................... 26
4.2.3 Menu mode...................................................................................................................................................... 28
4.3 Configuration............................................................................................................................................................ 31
4.3.1 A1 configuration menu items............................................................................................................................. 32
4.3.1.1 AUDI SETTINGS...................................................................................................................................... 32
4.3.1.2 DISPLAY SETTINGS.................................................................................................................................... 33
4.3.1.3 SH RTCUTS.............................................................................................................................................. 34
4.3.1.4 FACT RY SETTINGS................................................................................................................................... 35
4.3.1.5 INSTALLED PTI NS................................................................................................................................. 36
4.3.1.6 NETW RK................................................................................................................................................ 37
5 Firmware update............................................................................................................................................................... 38
5.1 Preparing the USB stick............................................................................................................................................. 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 Technical highlights
CH products are proudly designed and manufactured in Switzerland by CH Precision Sàrl. ur engineers have put all their know-
how into bringing you the A1, a top performances future-proof modular two output channels power amplifier with USB flash-drive
firmware update and Ethernet control capabilities. As all CH Precision products, the A1 is highly versatile: a single A1 can be used
as a stereo power amplifier (with two mono input boards), or a pair of A1 can be used as mono power amplifiers. Even in
monaural mode, 4 setups are possible: left /right mono mode (the transformer of each A1 is dedicated to a loudspeaker, but only
one output board is used), bridged mode (to nearly quadruple the available power per channel), passive bi-amp (each channel
powers a specific speaker driver) or active bi-amp (when an active crossover network is placed between the preamplifier and the
A1). Moreover, multiple A1s can be chained for ultimate performance, using multiple A1s per speakers.
For increased flexibility, the A1 also provides two unique features: global/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 any speaker on the market. The
amplifier gain can also be adjusted over a 24 dB wide range, by 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 connectors are
available (balanced XLR, single-ended RCA and BNC). Unbalanced inputs can be configured as high impedance input, or a 300
hm load can be engaged to match the output of 50 or 75 hm D/A controllers or preamplifiers. A pass-through XLR line-level
output is also provided for daisy-chaining multiple A1s.
A1 main components
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(1) utput coil for HF immunity
(2) Argento Audio speaker terminals
(3) Monaural analog input boards (each A1 can be equipped with 1 or 2 such boards)
(4) Mains switch and power cord receptacle
(5) USB (firmware update) and RJ-45 (control) board
(6) Adjustment shafts and screws
(7) Power supply regulation boards
(8) Heatsink-mounted monaural amplifier boards
(9) User interface buttons
(10) Rectifying diode bridges, mounted onto the front panel
(11) Custom rectifying capacitors
(12) Main analog star-ground oxygen-free copper plate
(13) AM LED display (on front panel)
(14) Standby power transformer (ensures green mode Standby)
(15) Main power transformer
1.1 Unmatched flexibility
The A1 offers unmatched system integration flexibility. Not only does it provide multiple modes of operation (stereo, mono,
bridged and active or passive bi-amp) but is also provides adjustments to match speaker impedance and sensitivity through
feedback and gain controls. perating modes can be selected by the user from the A1's front panel. In addition, multiple A1s can
be daisy-chained for ultimate performance in multi-amplification systems.
1.1.1 Operation modes
The A1 integrates two power amplification channels and provides the option to support a single or dual input boards. In its default
configuration, the A1 is delivered with a single input board and provides following modes of operation:
•Bridge mode: In this mode, the A1 operates as a very high power mono power amplifier, where both amplification
channels are used in balanced mode for a single audio channel. When configured in Bridged Mono Mode, the A1 can
deliver up to 350 W under 8 hm. It is optimal for high impedance speakers in large rooms, requiring large voltage
swings.
•Monaural mode: In this mode, the entire power of the transformer is dedicated to a single output channel. In Left or
Right Mono Mode, the A1 can deliver 550 W under 1 hm. It is optimal for low impedance speakers, requiring large
amount of current.
•Passive bi-amplification mode: In this mode, the A1 operates its two power amplification stages in parallel, each channel
driving a different speaker terminal with the same signal. Feedback and gain can be adjusted independently for each
channel to best match the individual speaker sections. In Passive Bi-Amp Mode, each channel delivers 100 W under 8
hm. It is optimal with speakers with more than one binding post pair on its passive crossover filter network.
By adding a second input board, the A1 provides 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 shared among both amplification channels and the
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A1 delivers 100 W under 8 hm per channel. It is the configuration used when a single A1 drives a pair of speakers.
•Active bi-amplification mode: As for 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 cross-over is generally used to split the signal into different frequency bands
between the system controller/preamplifier (such as CH Precision's L1) and the power amplifiers. In the Active Bi-Amp
Mode, the A1 delivers 100 W under 8 hm on each channel. It is optimal if the speaker has an external active crossover
filter network.
1.1.2 Feedback control
ne of the A1's most unique features is its user controllable feedback. This feature provides control over the ratio between global
and local feedback applied in the A1'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 cross-over are different and we highly recommend to try out various settings to find the best match with the
connected loudspeakers, especially if the A1 is driving a complete full bandwidth loudspeaker. In multi-amplification systems,
different feedback settings are commonly used for the various speaker sections opening a whole new level of performance. We
recommend to start with pure local feedback and increase the global feedback until the bass are tight enough for your personal
taste. Feedback settings can be adjusted on the fly from the A1's front panel.
1.1.3 Gain control
The A1 provides an integrated gain control with a 24 dB range and 0.5 dB steps. This gain control allows for optimal matching of
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 is conveniently accessed by a front panel control and can be set on the fly.
1.1. Bias adjustment
The A1 provides an advanced bias control circuitry that not only follows slow temperature variations, but also accurately takes into
account all the dynamic aspects induced by transients in the musical content.
1.2 Advanced monitoring circuit
1.2.1 Power monitoring
Each power amplifier board is equipped with a DSP that monitors the instantaneous voltage and current output of each A1's
channel. Both values are sampled at around 100 kHz, ensuring peak values are properly detected. This circuitry has several
purposes: give the user a feedback of the peak power fed to the speakers, and detect malfunctions such as short-circuits or
amplifier damage.
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1.2.2 Temperature monitoring
The DSPs are also responsible for reading both the power transistors and the radiators temperatures. If the temperature gets
excessive, the class-A polarization is turned off, forcing the A1 to work in pure class-B. If removing the output stage bias current is
still not enough, and the temperature keeps rising, the A1 will protect itself by entering standby mode. Please note that under
normal conditions, none of the above should happen.
1.3 Mechanical construction
The A1 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 1200 VA toroidal transformer and custom rectifying capacitors sitting in the central position of the unit. Argento Audio
internal wiring is used throughout the unit and binding posts from the same manufacturer provide the best possible interface to
your speaker cables. The area where the air flows to cool down the amplifier is isolated from the rest of the A1, ensuring all
electronics are preserved from dust accumulation. Pin assembly of all chassis elements provides smooth joints between elements
while screws every 6cm ensures protection against electromagnetic interferences. First class mechanical and chemical surface
treatments provide the luxury finish of the A1.
Four steel feet support the unit. Each feet ends with a elastomer ring to sit on delicate surfaces but is also equipped with a height
adjustable steel spike to fine tune unit positioning. 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 any stacked unit. Special shaft covers are provided to interface with
the spikes of the stacked unit. 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.
The area where the air flows to cool down the amplifier is hermetically sealed from the rest of the A1, ensuring the electronic
circuitry is protected from gradually gathering dust.
1. Modular architecture and slot-in boards
The A1 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 in a vertically mounted mother board with optional boards plugged into it. ptional boards
provide audio functionality and connectivity to other equipment. There are two types of slot-in boards:
•ANAL G_IN: provides mono single-ended RCA and BNC (both configurable as either high impedance or 300 hm
terminated) and balanced XLR analog audio input. ne (left or right) or two (left and right) such boards can be fitted
into the A1. By default, the A1 is factory delivered with a single ANAL G_IN board.
•C NTR L: provides a USB port for software upgrade and an Ethernet port for command. The C NTR L board is factory
mounted in each A1.
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