Monday, 8 August 2016

First component built

While the circuit for the amp is in the design phase I've decided to prepare one of the simpler stand-alone components - this is strictly a "nice-to-have" but I've decided that the amp will have a 5V USB socket on the back for running a USB-powered source accessory.

Currently I'm running a Sony integrated, which the valve amp will eventually replace. Connected to one of the inputs on this is a Chromecast Audio, which I'll run into the valve amp when it's built.

So with this in mind, I decided that a simple voltage regulator circuit running off the heater supply would do the job. However most linear regulators have a 2v dropout voltage, meaning that the input voltage must be at least 2v higher than the output.

However, the LM2940CT-5 regulator has a 0.5v dropout voltage, which is handy because when putting a bridge rectifier across the 6.3V I'll be seeing just a shade over 6V DC.

So, a bridge, a handful of capacitors, a voltage regulator and a heatsink, and a USB A socket.. assembled in the correct order, should give us a nice clean stable 5V of USB power.

This is the finished article – it doesn't look beautiful, it's just made on a piece of stripboard. But it's been tested and works 100% fine with the Chromecast.

(Finished as in electrically finished... I'll probably do something nice about the rough edge on the stripboard, and maybe I'll get a flush-mount USB socket rather than using the socket right on the board. OR maybe I won't even bother if space is too tight, and just keep the Chromecast on its own external supply. Like I said, this is a nice-to-have rather than an integral component!)

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