The δ2 relay-based stereo input/output selector
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Overview

δ2 ("delta 2") is a high-end stereo input and output selector board. It features a unique and flexible design, and uses high quality miniature latching relays to neatly achieve a level of functionality unattainable with conventional mechanical switch-based selectors. δ2 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. δ2 is fully passive, adds no distortion of its own, and with the δ1 relay-based R-2R stereo attenuator, offers a total amplfier-control solution.

A populated δ2 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.

δ2 supports the installation of up to eight relays, each one supporting a "port". Each port can be set up to be an input port or an output port. You decide the configuration that's right for your project -- all ports could be set up as input ports (for input selection of up to eight sources), or all as output ports (for outputs to up to eight targets), or a mix of port types as long as the total number does not exceed eight. Note that due to DPDT relays, a "port" actually comprises both stereo channels.

Input ports operate in a one-of-many model, where only one port from the pool can be selected at a time. However, output ports can work in either one-of-many or any-of-many model. The latter is called "Multi-Out", where every port can be independently enabled or disabled. This is selectable at run-time using the LCDuino-1's infrared remote control.

Under LCDuino-1 management, turn-on and turn-off muting delay functionality is provided. Before power is turned off, all output ports are first disconnected, and remains so after power is turned on until a user-settable delay time is elapsed. This helps prevent thump noises from being passed to the output target(s).

All parts are through-hole (no surface mount devices) to make the δ2 easy to build. See the Parts list section for details.

The LCDuino-1 board supplies power to the δ2 board and communicates with δ2 via an I²C bus. Each δ2 board uses two I²C addresses, which are set by jumpers.

One δ2 board contains two stereo unbalanced channels. You may install up to two δ2 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 δ2 boards in your choice of enclosure. See the Circuit board section for more details.

δ2 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 δ2 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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