3e Audio Amp Construction

In the November 2018 issue of IEEE Spectrum, Executive Editor Glenn Zorpette returns to the world of high-performance DIY audio in our Hands On column. In this appendix, he goes into greater detail about the construction and provides a complete parts lists with links to suppliers.

Construction Tips

Chassis: Cut the rectangular hole for the power-inlet module using a nibbler tool. Cut the hole slightly smaller than you need and file it out for a smooth finish. For the large round holes for the XLR audio connectors, use a hole saw, with teeth designed to cut metal, or use a knockout punch, such as a Greenlee. The power transformer is heavy, so support it with four rubber bumpers mounted directly below it on the underside of the chassis and put two more bumpers on the two far corners of the chassis, for a total of six bumpers supporting the chassis.

The deluxe chassis comes from Landfall Systems. It is sturdily made of 0.125"-thick sheet aluminum, and it is 16.5" wide by 9" deep by 3.25" high (normally we use S.I. units in Spectrum, but as Landfall Systems is a U.S. supplier, I'm quoting the imperial measurements I used to order). For an extra $25, Landfall will laser-cut the holes in the front and rear panels to your specifications (it's best to measure and drill the holes in the bottom plate—for the PCB standoffs and the rubber bumpers—yourself). I can provide a sketch for anyone pursuing this option; write to g.zorpette@ieee.org.

• Power transformer: The power transformer, AnTek AS-2222 or AS-3222, has two primary and two secondary coils. It is capable of 230- or 115-volt input, so for U.S. mains, wire the two primaries in parallel. Connect the transformer's two red lead wires to the mains-load side of the on-off switch, and the two black leads to the neutral side. Similarly, connect the transformer's secondary leads in parallel. Connect the two blue leads to one of the two input terminals on the power-supply board, and connect the two green leads to the other terminal.

The quick-disconnect connectors that fit on the power-supply-board terminals have dimensions as follows: 5.21 mm (0.205") wide by 0.81 mm (0.032") thick by 7.75 mm (0.305") long. Yes, it's a slightly odd size.

• Indicator light: Power the LED indicator light with the + 29-V DC from the power-supply output and limit the current with a 10k-ohm, ½-watt resistor.

• Power-supply board: The kit for the power-supply board comes with four Nichicon UVY1J682MRD electrolytic capacitors. They're 6800 µF, 63 V, and they're plenty good. But a reasonable upgrade option is to use Nichicon UKW1J682MRD capacitors. A set of four from Mouser costs $24.64.

• Amplifier board: The amplifier board comes with premade cables and terminals for the signal-input and power connections. For the signal-input cables, the wire gauge is so fine that you should protect and support them with a short segment of heat-shrink tubing where they connect to the panel-mount XLR solder cups. Or, better yet, make a couple of new input cables yourself, using thicker-gauge input wires. To do that you need the plastic, 3-socket, female half of a JST connector, with a pitch of 2.54 mm. They are readily available on e-Bay.

Bill of Materials