The α10 stereo pre-amplifier
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Overview

α10 ("alpha 10") is a high-performance stereo pre-amplifier which integrates the AMB projects listed below. A brief summary of each is provided, please visit each of the project sites for details.
α20 line stage amplifier
At the heart of the pre-amplifier is a pair of α20 line stage amplifier boards (one for each stereo channel). Its fully-complementary, all-discrete circuit topology featuring JFET input stage has very low noise floor, wide bandwidth, high speed, low distortion, high input impedance and low output impedance characteristics. The old JISBOS v1.01 buffer amplifier may be used in lieu of the α20, but it is unity-gain only.
LCDuino-1 display I/O processor
LCDuino-1 integrates a front-panel LCD display to show input/output selections, as well as volume attenuation settings with a bargraph and a numeric dB readout. It also has a number of other configurable display options and modes, including a real-time clock. LCDuino-1 supports a wide array of off-the-shelf infrared remote controls for all pre-amplifier functions. Based on an Arduino-compatible platform, it runs special open-source firmware which is field-upgradable with a special USB cable.
δ1 relay-based stereo stepped attenuator
Using eight highly-reliable latching miniature relays with gold-alloy clad silver contacts, the δ1 volume attenuator, controlled by LCDuino-1, has 256 precision steps in 0.5dB increments from 0dB to -127.5dB with excellent channel tracking accuracy. A "drive-by-wire" motorized front-panel potentiometer serves as an "valuator device" to the LCDuino-1 processor (in addition to the remote control), but the audio signal does not pass through the potentiometer.
δ2 relay-based stereo input/output selector
Also controlled by LCDuino-1 and using the same type of relay as δ1, the δ2 input/output selector offers switching for up to eight stereo inputs and outputs. It selects one stereo input at a time, but could select zero or more concurrent stereo outputs. δ2 provides muting delay function for all the configured outputs at turn-on. Between δ1 and δ2, the LCDuino-1 also implements a user-configurable level-matching system, so that when switching input and outputs, the playback volume can be made to be relatively equal regardless of input source or output target.
σ22 dual-rail tracking regulated power supply
The σ22 has ultra low-noise, excellent line and load regulation, low output impedance, wide bandwidth, and soft turn-on characteristics. It provides the purest possible DC rails to the α20 line stage amplifier boards.
σ25 single-rail regulated power supply
The σ25 regulated power supply provides a stable, always-on 5V housekeeping power to the LCDuino-1 subsystem.
A special α10 backplane board allows the above to be plugged-in as "modules", minimizing internal wiring, maximizes accessibility and serviceability, and greatly enhances neatness and appearance. The backplane has ground planes on both sides of the board (with separate areas for analog signal ground and digital ground), providing a rock-solid ground potential reference and helps to shield noise and interference. Logical plug-in module arrangement and careful trace layout of the backplane board also ensures short signal paths and vanishingly low inter-channel and I/O port crosstalk.

The integration of these modules and backplane results in an elegant stereo pre-amplifier with an uncluttered front panel, tidy and modular interior, plenty of input and output connectivity, convenience of IR remote control, excellent test-bench performance, and great sound.

Note that α10 is an audiophile-quality stereo line stage pre-amplifier. It does not contain a phono stage, a tape loop or tone controls. If you wish to use an analog turntable, AMB recommends the use of an external high quality phono stage for best results.

Some photos of AMB's reference α10 pre-amplifier (click to enlarge):

The scope of the α10 project

The α10 project is primarily centered around the α10 backplane board and each of the plug-in modules listed above. To build a working amplifier, you will also need a AC power supply of the appropriate specifications, as well as select and/or build enclosures to house everything. The AC power supply can be located in the main pre-amplifier enclosure, or in a separate enclosure for maximum isolation from magnetic field interference. The information in this website assumes that you have separate enclosures.

WARNING: Building the power supply for the α10 would require that you work with AC line voltage, which is a lethal shock hazard. If you don't know what you're doing, please ask someone who is experienced to help you. (See the disclaimer).

What skills and tools are needed

You should know how to read a schematic diagram and correlate it to the circuit board layout, identify electronic parts and their pin-outs, have decent soldering skill, and be proficient with a multimeter. You need at least a basic set of tools for electronics work, such as a good soldering iron and accessories, screw drivers, needle nose plier, diagonal wire cutter, etc. For the chassis case, you will also need to be familiar with using the tools that are necessary, such as an electric drill, bits, center punch and others.

Why not offer a full kit

AMB is not prepared to stock all the needed parts and offer them as a full kit. This amplifier also provides a number of customizable options that makes it unwieldy for such a kit. Lastly, this amplifier is AMB's contribution to the DIY community rather than a for-profit product, AMB cannot assume the commercial support role that might be implicit with a full kit.

Why not offer completed amplifiers

This is intended to be a project for DIYers, and AMB is not set up to manufacture completed amplifiers.

Where to get help

Be sure you read all the information at this site. If you cannot find an answer to a question, or encounter a problem you cannot solve, the best place to get support is the AMB DIY audio forum. Search the forum for an answer before asking a question. Your question may have already been asked and answered.


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