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The "Butte" DIY solid-state headphone amp
This is a DIY version of a solid-state headphone amp that was sold commercially for a little while. It's basically the same circuit as the Apex Butte, but has been changed to a through-hole assembly, and a few parts changed to make it less expensive to build.
It's an excellent first-time project. The detailed assembly manual gives step-by-step directions - I recommend that you download it and have a look. The total cost (as of 2/2015) is $76 not including an enclosure. You can buy a matching enclosure on eBay (shown in the photos above), or make your own.
All components are mounted on a single PCB, which is available from the pmillett.com eBay store. All parts (including the power supply and knob, but not the PCB or enclosure) are easily sourced from one place, Mouser Electronics. To buy the parts, all you have to do is load the Mouser BOM, and hit "Order Project". More detailed instructions are available in the assembly manual.
The amp circuit is straightforward, using a single power opamp. The OPA552 is a very good choice for this use - it has exceptionally low distortion and good drive capability. An optional CCS circuit can be used to draw current from the opamp output to the negative supply, essentially biasing it into class A for very small signals.
It has two inputs on the rear panel, one RCA, one 1/8" mini stereo phone jack.
The power supply is designed to be simple and affordable. It uses an AC wall transformer, and a voltage-doubler rectifier to generate about +/-18V from a 12V transformer. Linear regulators are used to provide +/-12V to run the amp.
Here are some supporting files:
The PCB and matching (optional) enclosure are available on eBay.