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Old 28th March 2016, 11:21 AM   #391
DIYBras is offline DIYBras  Brazil
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Only one side JFET will work only with DAC chips with enormous current offset, and I don't know one with such high current. For offsetting this current we put one JFETs on low side for each high side JFET, resulting in original circuit
Using one JFET "per high/low side" instead a pair (resulting in one JFET for high side and one JFET for low side) results in higher input impedance, and for me works flawlessy for several DAC chips, like TDA1541 or AD1860 and cousins.
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Old 28th March 2016, 04:55 PM   #392
donovas is online now donovas  South Korea
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Im sorry here i gotta scratch my thick skull.

Could you please elaborate on high/low design?
Are you saying that you simply split the original zen i/v?
Wouldnt they recombine when fed from the same output of a dac tho?

Im using it with tda1387 so your method might be the ticket i need
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Old 29th March 2016, 04:21 PM   #393
DIYBras is offline DIYBras  Brazil
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Some concepts at attached image.

The TDA1387 have a 1mA output offset, resulting very low current to use only with high side JFETs only, even if with only one JFET (one cell). Maybe this will work but with far-reduced performance.
So one can use high+low side as always, but is good to check the resulting voltage offset in TDA output pin and to check resulting JFET drain voltage. My adjustable MOSFET option can be adjusted for desired voltage offset. Of course, the adjustment can be applied to JFET version. The TDA1387 supports 0V to 1/6VDD voltage offset in their output pin. Or probably 1mA will not change things too much: experiment with "original" first. For alternative DACs using JFETs, search on ZEN-CEN-SEN thread (http://www.diyaudio.com/forums/digit...erter-183.html). In this thread probably one can find most resources about the JFET version/variants, since some members probably will be using chips like TDA1387.

PS.: I don't mention one thing yet: since low side devices in your drawing are N-channels, these don't contribute to AC output. You can dispense the "low side" capacitor and use only one attached to "V+" side, and gain a little output voltage. But is good to maintain the "low side" resistor (the resistor to V-) to better equate low side/high side JFETs dissipation.
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File Type: png Concepts.png (402.9 KB, 369 views)
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Last edited by DIYBras; 29th March 2016 at 04:45 PM. Reason: Additiona data
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Old 30th March 2016, 06:16 PM   #394
donovas is online now donovas  South Korea
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Thank you, i sort of understand. The 'zen' like design would certainly be economical for me since i can use 117 instead of 170.

Do you think the performance will be significantly lacking compared to zen iv? Ill be building the single ended design soon but wont have the zen to compare for a while.
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Old 30th March 2016, 07:58 PM   #395
DIYBras is offline DIYBras  Brazil
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http://www.firstwatt.com/pdf/art_zen_iv.pdf

The Nelson Pass D1 I/V is made with single-ended operation. My MOSFET design is a sort of "D1 push-pull version". JFETs will work in Single Ended too. Only "second harmonics" will rise versus the push-pull version, not much if one measures the resulting drain voltage (rules more or less like the original ZEN).
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