I'm currently working on my own beta22 (it's all wired up without a chassis and already sounds fantastic) and I have enough parts left over for a balanced (4 boards) build, apart from the gain resistors/capacitors (4 resistors and 4 capacitors per board, cost ~£1/board). This isn't a problem as to finish the build you'll need to put in an order for all the trimmings. All parts are as recommended, sourced from the AMB shop, digikey, mouser and farnell a few months ago. Includes blue LEDs and molex headers/housings.
As a bonus I have hand matched all the BJTs (all 200 of them!) into pairs and quads as necessary. I ordered the input JFET matching service too, and the mosfets come matched, so that's 8/10 of the "device matching" steps done for you already. Only 3/10 are recommended for "excellent" results. A popular criticism of discrete amps like this is that the components aren't matched closely enough. The beta22 is pretty insensitive to this, I think the official line is now that only 1/10 is needed for a reference quality amp. Nevertheless it gives me peace of mind that it's working as well as it can be.
The total cost for the B22 stuff is £312.82. This is exactly what it cost me to source, but saves you the trouble.
I also have the parts for a sigma22, cost me/selling for £62.25. Parts are for +/-30V operation. It will happily power all four boards using a Y236405 transformer for example.
I shopped around for months for the cheapest combination of suppliers, so this is as low as it gets for recommended parts. Sadly I was hit by some taxes here in the UK so that's included.
The beta22 really is a world class amp, technically about as good as solid state can be (and measures far, far better than anything tube):
High power: For 2 channel: 0.75W into 300 ohm, 5.6W into 32 ohm, 18W into 8 ohm. For balanced it's 50Wrms into 8 ohm!
Frequency response: 0 to 2.5 MHz (+0dB -3dB) (yes, megahertz)
THD < 0.001% (more like 0.0003% at -5 dBFS with a 33 ohm load i.e. full power and a hard load to drive) It has a similar level of distortion to the DACT attenuator (now sold) which is SMD resistors and gold wire(!)
Slew rate 198 V/us (double for balanced! One or two orders of magnitude more than is needed, this is a very fast amp)
Output impedance < 0.01 ohms i.e. damping factor in the thousands.
Don't be put off by the complexity of the project. This is the first DIY project I've ever taken on and there were absolutely no problems. As long as you have the right tools and check and double check it's a piece of cake ;)
UK preferred. Payment in the UK by bank transfer. Elsewhere by paypal. You pay fees and shipping. Inspection/collection welcome in Oxford.
There are also a few other bits including Neutrik 3 pin panel mount connectors and Epsilon 22 backplanes :)
P.S. It's more elegant to power 4 boards with 2 sigma22 power supplies. It shares the thermal load and causes a current cancellation on the supply rails. I bought some spare spares ;) so actually have nearly everything for a second sigma22. If interested please send me a PM.
Edited by joeyjojo - 8/21/12 at 10:29am