Zen -> Cen -> Sen, evolution of a minimalistic IV Converter

[EUVL]

One day on the return journey of a business trip, I had an idea of using a JFET version of Leach’s MC headamp as IV converter for current-out DACs. A month later, various circuits were simulated, bread-boarded and measured, and prototypes with proper PCBs were built and tested. We also did listening tests using our own SD player and AD1865 DAC, and were very pleased with the results.

I took them to Jan Didden one evening for some distortion measurements with his Audio Precision System One. He was so impressed that he wanted to include the article about this development in his Linear Audio Magazine, Volume 2, due out at the beginning of September. In support for Jan’s enthusiasm in running the magazine, I duly obliged.

So you can now read the entire story in detail in Linear Audio. To facilitate experimentation of the circuits, we shall make available an evaluation kit, but only if there is sufficient interest (minimum 60 sets).

Jan has generously agreed to me publishing the schematics, bill of material, PCB layouts, and some measurement results here. So in theory you can build the circuit without reading the article. But I strongly suggest you do, not only to understand how it works, but also how to adapt it in the many possible configurations to your need.



Patrick

[EUVL]

Here are the schematics as published in Linear Audio, courtesy of Jan.

CEN for complementary, SEN for single ended.


Patrick

[EUVL]

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[EUVL]

As on the front cover of Linear Audio Vol. 2.


Patrick

[EUVL]

Sen IV 10kHz +/-1mA Square Wave
(Riv = 3k, Green = Vin for VCCS, Cyan = Vout Sen IV, unfiltered)

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[EUVL]

FFT of Sen IV using 20k series resistor at input (Audio Precision System 1)
(Blue : Signal Source, Magenta : IV Voltage Output)

You need to refer to the article to see why we use this as the I input, as compared to a low distortion VCCS.
The VCCS turned out to be not low distortion enough at about -100dB.


Patrick

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[EUVL]

Contents of the Evaluation Kit.

Actually there is no longer a need for me to throw in 40 pairs of 2SJ74s, as Spencer has stock now.


Patrick

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[EUVL]

The relevant links :

Moving Coil Cartridge Head Amps
http://www.lcaudio.com/images/Accessories/mcstepbig.gif
Zen I/V Converter


Patrick

[EUVL]

Note that the performance in post #6 was based on a transimpedance of 2700R, as compared to 500R of the original ZEN IV.

On Spice simulations using identical component models (active and passive), the CEN and SEN has a factor of 4 to 6 less distortion than ZEN, using 500R transimpedance in all 3. The distortion is too low for me and Jan to measure because we simply do not have a current source with low enough distortion (-130dB).


Patrick

[Variac]

Patrick,

Certainly of great interest and use to me. Good Job!

Also glad I'm subscribed to Linear Audio, we need to support such a resource...

Mark