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rjm 7th September 2011 11:31 PM

RJM Audio Sapphire Headphone Amplifier rev14a1 kit
2 Attachment(s)
Announcing a total of 10 Sapphire kits will be available at a cost of $100 each.

The Sapphire desktop headphone amp is a two stage, voltage gain + current gain design, with a 4 transistor diamond buffer typically running open loop as the output stage. Typically about 10 mWpc of class A output, 1-2 Wpc class B output, and a total quiescent dissipation of 6-7 W stereo. The board revision is 14s1. BOM and info attached, or see the Sapphire web page and RJM Audio products page for more information.

The kit consists of a pair of boards and all the parts for the boards. Volume control, chassis hardware, transformer(s), rectifiers, are not included.


rjm 13th September 2011 11:22 AM


I now either have the parts delivered already or they are shipped out and on their way to me.

The boards are on their way, by DHL, I should see them by Friday. Photos then.


jtktam 13th September 2011 12:58 PM

i am interested in a few

rjm 13th September 2011 11:34 PM

There are still a few kits left, just pm or email me.

rjm 15th September 2011 08:06 AM

2 Attachment(s)
Spiffy yellow Sapphire boards arrived this afternoon.

I'll be putting a set together shortly just to double check everything works as it should.

A quick check showed one minor mistake on the BOM: the heatsinks are a little too wide. I have ordered some of the smaller size and these will ship with the kit.

The correct Mouser pn for the heatsinks is 532-577002B00.


rjm 15th September 2011 05:13 PM

And another mess-up in the BOM, now fixed.

The Mouser pn for R10,11 was for a 330k ohm resistor, not a 300 ohm one. One letter difference in the part code.


Everything else checks good. Using the R10,11 salvaged from the prototype, I'm listening to the new boards as I type this. The output bias current is about 3x more, within 20% of my calculated value. No quantum change in the sound over the prototype version. Right now it seems slightly heavier, warmer sounding, but the filter caps are haven't run in yet so it's too early to make a proper assessment.

rjm 17th September 2011 07:51 AM

Kits will be delayed while I source new heatsinks and R10, R11. Estimated ship date Sept 26th.

Boards and circuit values are thoroughly checked and confirmed good. It was just an error in the BOM part numbers, I ordered the wrong parts by mistake.

rjm 26th September 2011 06:54 AM

Most kits shipped today. I have two left.

rjm 3rd October 2011 05:21 AM

All the kits have now been sold.

rjm 9th December 2011 05:05 AM

That was fun. Let's do it ... again!

Planning a second run, to be organized over the holidays when I am marginally less busy with work.

Let me know if interested in boards or kits for the Sapphire.

Also - am taking requests for any changes based on peoples experience with the initial offering. So far response as been positive, though not flawless. More people encountered difficulties with the build than I would like, even as the final sonic results have generally met expectations.

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