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Old 19th November 2013, 11:34 PM   #111
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Richard Murdey
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Hi Fran,

I had hoped those kits would have kept you occupied in the workshop for a little longer, its not even December yet!

You promised pics. I wanna see pics.

Anyway, I'm glad to hear you got both projects up and running without any problems. Certainly the 2-in-1 approach is a novel one, and makes listening evaluations that much easier. Given the complementary nature of the two circuits its actually a nice option: to select the amp based on mood, headphone choice, and even the individual song.

"kmultiplier" is probably a capacitance multiplier, basically a simple voltage regulator but with with a voltage divider rather than a fixed reference. The X-reg falls into this class, but the "classic" version is just a filtered voltage divider with the output tied to a transistor gate/base: link
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Old 20th November 2013, 06:27 AM   #112
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Quote:
Originally Posted by woodturner-fran View Post
RJM Audio Sapphire Desktop Headphone Amplifier


Tell me more about the kmultiplier - is that extra capacitance?

Excuse my ignorance!

Fran
It is a special cap multiplier that has very low output Zo due to the use of a CFP.

I placed it between the smoothing caps and the shunts... it took the J-Mo to a very high subjective level.

Keantoken's CFP cap multiplier

The K Multiplier
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Old 20th November 2013, 06:51 PM   #113
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Ah, ok. I used a salas shunt, so not quite as easy to add the multiplier.... Pics later, but I'll tell ya now, it ain't pretty...


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Old 20th November 2013, 08:24 PM   #114
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I used two BiB and before that two kmult.... you might want to try it
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Old 20th November 2013, 09:47 PM   #115
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OK, I'll investigate!

A pic.... as I said, it aint pretty. Thats the shunt at the back, the J-Mo in front of that and then the 2 boards for the Sapphire to the right. Single pair of input RCA jacks at the back with a switch to swap the signal from one amp to the other. 2 x headphone jacks and 2 x gigawork pots complete the wiring.

Both amps are silent as the grave, with just a touch of hiss on the Sapphire at full volume (which you would never go near anyway). At all normal to very loud listening levels, no hum, hiss, etc. etc. If it wasn't for the LEDs in the shunt and the bit of vibration from the EI Tx you wouldn't know it was on.

The lid has yet to go on, and of course the front plate which I have yet to make (this is a recycled box from a cassette deck).


Fran
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Old 20th November 2013, 11:11 PM   #116
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Anyone who thinks it looks ugly is advised to wait until Fran gets started on the cabinetry. It will blow your mind.

Fran, are the power supplies completely independent after the AC line? How are the three power transformers divided out between the four amplification channels?
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Old 21st November 2013, 06:33 PM   #117
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I like it a lot....., mine is p2p and uses two shunts with special vref and output cap arrangement
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Old 21st November 2013, 09:50 PM   #118
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The two matching transformers (leftmost ones) supply the sapphire, one for each board. The rectifiers are mounted right on the transformer terminals. The other one then supplies both channels of the J-Mo via a salas shunt - the PCB mounted vertically on the heatsink at the back.

Nothing shared after the back of the IEC..... I'm getting lazy maybe putting it all in the one box, but it helps keep the box count down. I'm still thinking about finishing the front of it - whether I go for a wood or acrylic, not sure yet. The other thing that I might do is split the supplies for the J-Mo and go dual mono on that. I reckon I can fit it all in, especially if I stacked 2 toroids.

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Old 10th December 2013, 08:39 PM   #119
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Richard - have you ever tried to use some LEDs instead of R7/R2?


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Old 11th December 2013, 12:18 AM   #120
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No I haven't. Replacing the MOSFET source resistor R7 with a current source of some sort will reduce distortion, and a similar trick may work for the JFET - I haven't looking into that side of it.
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