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RJM Audio Sapphire Headphone Amplifier / Preamp Prototype Boards Available

post #1 of 13
Thread Starter 

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

post #2 of 13
Thread Starter 

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

 

 

post #3 of 13
Thread Starter 
The prototype version is finished.

500

There is a web page for this project, here.
post #4 of 13
Thread Starter 

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.

 

sapphire14a.png

 

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

 

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

 

http://phonoclone.com/pcb.html

post #5 of 13

Hmm, this looks interesting. The price seems right as well... (ack, it's not like I need to add yet another project to the list rolleyes.gif)

post #6 of 13
Thread Starter 

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.

 

 

post #7 of 13

I felt this deserved a bump, although I know its an old thread. I haven't been posting here much in the last few years, but a recent headfi event re-ignited my interest.

 

I've just completed the build on this amp and I'm really impressed with how it sounds. My point of comparison is a 24V aikido using 6GM8 tubes and mosfets outputs (the aikido HPA, now disconitnued I think). I have found in the past with direct comparisons that the aikido amp can really drive my k701s to sound really good - really firm bass and not at all "toppy". Well, to my surprise the Sapphire sounds bloody good and is the match of the aikido. Also matches well with the HD600 although I haven't listened as long with those.

 

Fran

post #8 of 13

No love for this amp?!?

 

You guys are missing out!!

 

Also from the same stable - the J-Mo amp - even simpler to make, and magic too for low impedance cans.

 

 

 

Fran

post #9 of 13

I am thinking about building one of these myself and was hoping to get some review feedback on it...

post #10 of 13

that right,really firm bass and not at all "toppy". Well, to my surprise the Sapphire sounds bloody good and is the match of the aikido. Also matches well with the HD600 although I haven't listened as long with those.

hDIQWz

post #11 of 13
Ditto. It's on my list now to try some other power supplies next, maybe a super reg or something to see how it sounds.

Fran
post #12 of 13
Thread Starter 

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

 

I've finished updating the web page to the current ver. 2.0 of the Sapphire circuit, and the new boards are due in momentarily.

 

 

(two-layer board, bottom trace shown)

 

 

 

The main change is to the diamond buffer, with new bias resistors R9, R10 to increase the current though the output stage for more class A power reserve. The rest is largely housekeeping and small refinements.

 

This being the first batch of new boards, 5 "tester" kits will be available at a special discount. Contact me if interested.


Edited by rjm003 - 12/10/13 at 4:09pm
post #13 of 13

Built this amp (Sapphire ver. 2.0) a few weeks ago. I have to say it's a mighty fine amp. Drives my HE-6 with ease. Great soundstage with almost speaker-like imaging. Terrific bass extension. 

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