RJM Audio Sapphire Headphone Amplifier / Preamp Prototype Boards Available

Two boards are required for stereo. I have four pairs available to anyone willing to be a beta-tester. Cost is $20 shipped (this is at-cost pricing, I'm just interested in having a few more people try this out.) PM if interested.

The Sapphire amplifier is a fairly standard op amp + diamond buffer. Zener diodes are used for voltage references. The boards have a jumper to switch from class A open loop to class AB closed loop operation, and the circuit values can be optimized use either as a headphone amplifier or a preamp. My own interest is class A open loop for 16 ohm headphones.

board

http://i55.photobucket.com/albums/g160/rmurdey/Gainbloc/sapphire10b.png

schematic (parts values shown are nominal placeholders, the final values depend on the application)

http://i55.photobucket.com/albums/g160/rmurdey/Gainbloc/sapphire10b-sch.png

I will have an excel worksheet/BOM available by the time the boards ship. I'm also working on a webpage for the project.

regards,

RJM

Beta version of the BOM is finished, but since I can't post attachments to this forum you'll have to visit the related thread at diyaudio to see it.

http://www.diyaudio.com/forums/solid-state/183588-headphone-amplifier-drop-replacement-phonoclone-3-vsps300-2.html#post2498279

Things moving along, slowly as usual.

I've settled the layout details of the "production" board revision 14a. The output and driver transistors are now mounted on a common heatsink to enable thermal feedback and prevent thermal runaway (both over and under current protection). No significant changes to the circuit per se. I've had my prototype version up and running for several months now with no issues.

Parts and boards, BOM, all info at the relevant web pages.

http://phonoclone.com/diy-sapp.html

http://phonoclone.com/pcb.html

I've decided to put out the initial run of boards as a kit will all the parts required for the PCB. You'll need to supply power transformers, rectifiers, a volume control, jacks and chassis hardware, but the boards are taken care of. That should simplify things for most people I hope.