Times change. I bought one from digikey for a whopping $5.50. Digikey has six versions of the chip (four of them reels, priced at about a 40% discount). Only the reels require purchase in large quantities. All six have identical specs.

http://www.amb.org/

prototype board and laquer isolated copper wire will do very well.

I’ve been in the headphone diy audio community for a while–generally, the mini^3 board will probably be sold by AMB, the guy who created it. Contact him via headwize for more info. I think he has an online shop somewhere–he gets a load of them professionally made, and redistributes the boards. You’ll probably also need to go through him for the ad8397, which, iirc, is not available in small quantities via digikey.

You might also require a bit of experience to build this particular amp–the main opamp chip here seems to have a pretty nasty reputation for oscillating like hell when you’re not careful with the soldering. Also don’t attempt to build this circuit without amb’s board (i.e. on protoboard or whatnot)–you’re almost guaranteed to have a fried opamp due to oscillations unless you know what you’re doing.

On PCB etching–look up inkjet pcb printer. There are published results of people consistently getting 3mils resolution. I’m actually building one right now–I’ve completely given up on the toner transfer method, as it hasn’t been working very well at all for me.

carlton: I think you make it sound harder than it is (0603′s). And you seem to be describing a full out smps psu, where a simpler boost converter would be adequate. But I agree its not for the average headphone enthusiast to attempt a design (although assembly could be possible).

greg: toner transfer or photoresist are the two main hobby methods. If you’ve got a laser printer, go w/ toner imo (http://www.fullnet.com/~tomg/gooteepc.htm). I would recommend buying if you require many vias, or value your time :P: http://claymore.engineer.gvsu.edu/egr326/PCBManufacturing