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Old 28th August 2011, 07:35 AM   #11
EUVL is offline EUVL  Europe
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> Also glad I'm subscribed to Linear Audio, we need to support such a resource...

Absolutely, which is why I agreed to publish the article at Jan's rather than here.


Patrick
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Old 28th August 2011, 07:37 AM   #12
EUVL is offline EUVL  Europe
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Those skilled in the art will spot the major difference to the ZEN IV and the Leach Headamp.
The floating power supply and the use of JFETs are keys to performance advantages.
Think Kirchoff's law.


Patrick
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Old 28th August 2011, 08:11 AM   #13
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Quote:
Originally Posted by EUVL View Post
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
This will be the first article i read in the new issue..!

Perhaps you could use the AN67 oscillator and an R2R like structure to generate a clean current source with some effort it should be possible to select the output impedance and the current swing you want.
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Old 28th August 2011, 08:31 AM   #14
EUVL is offline EUVL  Europe
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Jan & I were using the Audio Precision Oscillator which is as good as if not better than AN67, which I also have.
The Audio Precision can output up to 20V, which the AN67 cannot.

I can only ask you to read the article. It is unfair to Jan if I tell more here.

And I do want you to support him.


Patrick
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Old 28th August 2011, 08:41 AM   #15
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Quote:
Originally Posted by EUVL View Post
Jan & I were using the Audio Precision Oscillator which is as good as if not better than AN67, which I also have.
The Audio Precision can output up to 20V, which the AN67 cannot.

I can only ask you to read the article. It is unfair to Jan if I tell more here.

And I do want you to support him.


Patrick
I seem to remember FREX posting measurements on the AN67 displaying distortion of less than -160dB down from full scale.
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Old 28th August 2011, 08:48 AM   #16
EUVL is offline EUVL  Europe
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-160dB was the measurement limit of Audio Precision analyser.

The first measurement we did was on a HP339A.
It was some 20dB worse.


Patrick
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Old 28th August 2011, 09:38 AM   #17
EUVL is offline EUVL  Europe
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> It was some 20dB worse.

I meant the oscillator from the HP339A.


Patrick
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Old 28th August 2011, 11:36 AM   #18
rsdio is offline rsdio  United States
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Quote:
Originally Posted by EUVL View Post
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.
Regardless of why you use any particular input, how is it that your output has less noise than your signal source? Is there negative gain?
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Old 28th August 2011, 11:49 AM   #19
EUVL is offline EUVL  Europe
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The input was a 20Vrms sine wave from Audio Precision's functions generator, which was converted to 1mA rms input to the IV via a 20k series resistor.
The IV Converter output had a 2.7k resistor, and hence the output was 2.7Vrms.

Because the functions generator voltage was some 17dB higher than the IV Converter output, it was no surprise that the noise levels differed by about the same amount.

These are all explained in the article.


Patrick

.

Last edited by EUVL; 28th August 2011 at 11:52 AM.
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Old 28th August 2011, 01:41 PM   #20
EUVL is offline EUVL  Europe
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Thank you all for your support and interests in the Evaluation Kit via PM, despite not having read the article.

The article would actually answer many of your questions (such as which DAC type, ..., etc.). But it is not difficult to see that the original CEN or SEN circuit, like Nelson's Zen IV, is designed to work with bi-polar current output DACs with no offset voltage, such as PCM63, PCM1704, AD1865, ..., etc. With simple modifications, it can also work with DACS with either current offset, or voltage offset, or both.

We have tested and listened with AD1865 and are absolutely pleased with the results, especially with LCR polystyrene as C_iv. But of course we are always totally biased, and the truth is only when you get a chance to try for yourselves. There are still plans to try it with PCM1704, though we have some more work on the power supply for that DAC chip.

I think it is too early to start a GB of the Evaluation Kit. The article gives you a lot more info as to how the idea came about, how the circuit works, what the performances, are, what other circuit variations you can choose to suit your specific needs, ...., etc.

And there are many other articles in Volume 2 that it is well worth the very small price being charged.
Please give Jan your support. It is IMHO a noble course.

http://www.linearaudio.net/


Patrick

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Last edited by EUVL; 28th August 2011 at 02:01 PM.
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