The δ1 relay-based R-2R stereo attenuator
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δ1 ("delta 1") is a high-end stereo stepped attenuator implemented in a R-2R resistor ladder topology. It uses high quality miniature latching relays and precision discrete resistors to achieve a level of performance unattainable with conventional potentiometers or mechanical switch-based rotary stepped attenuators. δ1 is designed to be controlled by the LCDuino-1 Display I/O Processor platform, which provides a front panel status display, infrared remote control support, front panel controls, and many other features. δ1 is fully passive, adds no distortion of its own, and with the δ2 relay-based stereo input/output selector, offers a total amplfier-control solution.

A populated δ1 board - click to enlarge.

The use of latching relays means that the relay coils draw current only while switching, and the contacts do not lose their positions even when power is disconnected. Each side of the relay coils are driven by symmetrical circuits, featuring optional LED arrays to show activity for debugging purposes. The specified relays are highly reliable telecom-grade units with silver mechanisms and gold alloy contacts.

Designed to be highly configurable and customizable, δ1 supports the installation of five to eight relays*, which provides you between 32 and 256 steps of total control. You choose between 0.1dB, 0.5dB or 1.0dB attenuation per step*. You also choose the optimum attenuator impedance for your application. Use the convenient resistor value calculator to help you select the correct resistors.

All parts are through-hole (no surface mount devices) to make the δ1 easy to build. Several different resistor sizes are supported, which provide you with a wide range of choices. You can build a high performance system with standard 1% metal film resistors or a "price-no-object" configuration with foil resistors. See the Parts list section for details.

The LCDuino-1 board supplies power to the δ1 board and communicates with δ1 via an I²C bus. Each δ1 board uses two I²C addresses, which are set by jumpers.

One δ1 board contains two stereo unbalanced channels. You may install up to two δ1 boards per system* to support a stereo balanced configuration. Multiple δ1 and δ2 boards may be "stack-mounted" to reduce their enclosure internal footprint and to simplify wiring. There are several other mounting options available which makes it flexible and easy to install δ1 boards in your choice of enclosure. See the Circuit board section for more details.

For convenience, the δ1 board provides optional ground loop breakers which you may use in some configurations. See the Parts list and δ1 board assembly instructions sections for details.

δ1 is easy to build and set up, but due to many possible configurations and options, please be sure to read every section of this site (and the LCDuino-1 website) carefully before attempting to build it. If you don't thoroughly understand everything, ask questions in the AMB DIY audio forum, or consider having someone more experienced to build it for you.

AMB audio shop offers blank δ1 and LCDuino-1 printed circuit boards and some related parts. Other parts are available from online vendors. See the Parts list section.

* Limits imposed by LCDuino-1 firmware.

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 system also provides a number of customizable options that makes it unwieldy for such a kit. Lastly, this system 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 systems

This is intended to be a project for DIYers, and AMB is not set up to manufacture completed systems, especially in light of the large number of possible configurations and options.

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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