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Old 30th January 2014, 02:40 AM   #1631
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Join Date: Apr 2013
Sorry to continue insisting, perhaps you did not see my questions so here i go again. I'd really like any answer you could give me regarding the questions I have done to you.

First. Regarding the possibility that r1 and r2 may be changed from 560k to 200r to get a stable output with an offset in the input current (PCM1792). I know u are testing a solutions to this kind of DACs, but probably means the addition of a CCS. It is not my intention that you do special tests to get an answer, i only want to know if there is an error or basic theoretical impossibility to do it, and then decide whether it’s worth doing. Perhaps some value or other component that had to be modified, or increase the total number of Idss of each channel, or some other aspect.

Second. Is it possible to determine the offset voltage due to a mismatch of JFETs, keeping the circuit disconnected from a DAC? Perhaps connecting the input to ground?

Thanks.
Cheers.
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Old 30th January 2014, 03:40 AM   #1632
EUVL is offline EUVL  Europe
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a) There has been solutions by other people published here with the PCM1794, proven to work.
b) We have published a rough outline of our solution, and we shall publish the full solution when we are ready.
In our solution we did not have to change the two resistors to 200R.
c) The function of R1 and R2 has been explained in the article, which you can download for free.
d) If you wish to experiment with variants of the circuit according to your interpretation, you are most welcome.
e) You can always test any variations of the basic circuit in LT Spice (freeware) before building.


Patrick
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Old 30th January 2014, 03:46 PM   #1633
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Quote:
Originally Posted by EUVL View Post
a) There has been solutions by other people published here with the PCM1794, proven to work.
All of them mean the addition of CCS plus the corresponding PS for these, Servos as well.

Quote:
Originally Posted by EUVL View Post
b) We have published a rough outline of our solution, and we shall publish the full solution when we are ready.
Thanks for that, but I’m afraid that it will be a CCS. Don’t get me wrong, I’m not saying that CCS is bad; it’s just a personal preference that I don’t like CCS as the answer in this particular circuit.

Quote:
Originally Posted by EUVL View Post
In our solution we did not have to change the two resistors to 200R.
200R addition means no CCS, if it works, but the circuit consumption rise and the wattage of the resistor rise as well. Probably additional JFETs need to be added to increase the total Idss and handle the offset.

Quote:
Originally Posted by EUVL View Post
c) The function of R1 and R2 has been explained in the article, which you can download for free.
I already read the article, and the explanation about the r1 and r2 is just a potential divider to set the floating power supply symmetrically about input ground DURING START UP. But in the simulation that I load up in the post #1616, when lowering this resistors, the output signal gets 5.6 Vp-p (7.8 mA x 725R), and an offset of 4.5 V (6.2 mA x 725R). Overall, the output signal became consistent with the currents on the input (7.8 mA p-p, 6.2 mA DC), in other words, r1 and r2 work additionally during the normal operation. All of this off course, on the simulation.

Quote:
Originally Posted by EUVL View Post
d) If you wish to experiment with variants of the circuit according to your interpretation, you are most welcome.
Thanks, I was just seeking for basic errors that my proposal could have, nothing more.

Quote:
Originally Posted by EUVL View Post
e) You can always test any variations of the basic circuit in LT Spice (freeware) before building.
As I mentioning, I am already testing this ideas on SIM.

Last edited by HansoLu; 30th January 2014 at 04:13 PM.
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Old 30th January 2014, 05:36 PM   #1634
EUVL is offline EUVL  Europe
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We are known for simplistic circuits, so we don't add anything if they are not necessary.
But you are most welcome to report your findings here if you could improve on our solution.


Patrick
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Old 26th February 2014, 09:15 AM   #1635
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Quote:
Originally Posted by HansoLu View Post
To power the circuit, I utilized 2 separate regulated supplies with their own transformer (I did not use batteries) to achieve the 18 V required for each circuit. -Iout output of each channel from the PCM1792, were used.
What's the disadvantage with this configuration instead of batteries? Running a dual regulated supply and just floating the ground. Do you get drifting dc voltage on the output?
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Old 26th February 2014, 09:35 AM   #1636
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Default link for the buffer

Hi Patrick
please let me send a link for interesting buffer with floating ps with similar topology for CEN: Some other Source Follower COnfigurations
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Old 5th March 2014, 02:47 PM   #1637
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Quote:
Originally Posted by Painkiller View Post
What's the disadvantage with this configuration instead of batteries? Running a dual regulated supply and just floating the ground. Do you get drifting dc voltage on the output?
I didn't make a dual regulated supply, but two completely isolated PS, starting by using separated transformers for each. Of these, the positive and negative terminals of each regulated PS, was connected as suggested in the schematic. I do not use the term "ground" or reference for the negative terminal on both supplies, because these sources are floating.

Regarding noise, only by ear, I fail to perceive any of it at full Iout of the Dac (7.8 mA pk-pk). I only get some noise when using digital volume, which means lowering Dac pk-pk Iout and, increasing with it, the noise in proportion to the signal.
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Old 22nd March 2014, 05:03 PM   #1638
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Hello,

If anyone interested, I have 1/2 an evaluation pack (original) for sale.

1x Cen IV PCB
1x Sen IV PCB
2x Quad Jfet heat sink Type 10
2x Dual Jfet heat sink Type 0

PM me for details. (also posted in the for sale forum)
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Old 22nd March 2014, 05:59 PM   #1639
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Default Evaluation Kits and parts

Quote:
Originally Posted by mfrimu View Post
Hello,

If anyone interested, I have 1/2 an evaluation pack (original) for sale.

1x Cen IV PCB
1x Sen IV PCB
2x Quad Jfet heat sink Type 10
2x Dual Jfet heat sink Type 0

PM me for details. (also posted in the for sale forum)
I also have some parts:
8x matched 2sk170BL's from reliable FetAudio.com (7.6ma)
4x WIMA 0.1uF Polypropylene Film Capacitors
2x WIMA 330pf Pulse Film Capacitors
4x Nichicon MUSE BP 220uF 16v
4x PRP 560k 1% resistors
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Old 8th April 2014, 09:24 AM   #1640
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Default Kit Sold - Thank you

Kit Sold - Thank you

Quote:
Originally Posted by mfrimu View Post
I also have some parts:
8x matched 2sk170BL's from reliable FetAudio.com (7.6ma)
4x WIMA 0.1uF Polypropylene Film Capacitors
2x WIMA 330pf Pulse Film Capacitors
4x Nichicon MUSE BP 220uF 16v
4x PRP 560k 1% resistors
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