Zen I/V Converter

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#21
EUVL said:
This is a quick & dirty schematics just to show the idea of a cascoded complementary JFET IV.
I hesistated to call it cascoded Zen IV, as it is more of a "Blowtorch IV".

Balanced DAC current is fed to the sources of the input jfets, whose gates are tied to ground.
R2,3,19,21 are bias resistors for the folded cascode MOSFETs (say 200R).
Conversion gain (I to V) is set by R22,24.
One may add additional electrolytic caps to parallel R5,6,16,17.
And R1/18, R4/20 can be replaced by constant current diodes for further improved PSRR.
The rails can now be quick a bit lower than +/-30V.
And the choice is not affected by changes in IV conversion gain and first stage bias.
So one can increase R22,24 (say to 2.4k) and use multiple JFETs in parallel without changing Vsupply.
When using JFETs in parallel, R2,3,19,21 wants to be reduced by N (no.of JFETs in parallel).

No coupling output caps, but consumes quick a bit more current.


Patrick
Click to expand...



Problem with this is you would be stuck with balanced ouput and the input would require 2 extra DACs. R2R DAC chips aren't chip or easy to find these days.

If you forgo the coupling caps, the output would be around 0V, I would think that a simple servo filtered below 1 hz or less could null the DC offset and be cheaper than buying a quad blackgates. The lower cost would keep it Zen-like IMO 😉
 
#23
Just came across this new I/V stage which looks damn good 😀
I made a .pdf file of the article which I found a little hard to find inside DiyAudio, that could probably be attached on the first post too 😎

Best regards,

nAr
 

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#26
Hi guys,

Two of my favorite topics: UGS and IV converters.....in no particular order!

Philippe: since you use the ad1865 current mode is it safe to assume that this chip expects 0V at that pin ?

I'm thinking of trying this with a 1738 ( in a Shanling CD Player ) which expects 2.5V at the current output pin.

Just to compare with a Drek conversion i did with Zen-Mod's precious 😎 help 🙂

I made a mother board for IVs and PSU just so i could test different solutions....here is the chance.

Not that i'm unhappy with what i got but DIY is an itch that doesn't go away.........

Late edit: I'm curious about the UGS solution by will invest my effort on the present ZEN IV.
 
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#27
Maybe some of us, actually a lot of us don't like the sound of heavy NFB. I would say Mr PA0SU that this isn't the place to Pimp your website. You are kind of insulting a highly regarded designer and many of us take offense.

And Thankyou Mr Pass for sharing this new design with us, we do appreciate it.
 
#28
Hi guys,

Two of my favorite topics: UGS and IV converters.....in no particular order!

Philippe has posted a UGS based IV in the article coments,since one has to use use the ad1865 ( in his particular case ) current mode is it safe to assume that this chip expects 0V at that pin ?

I'm thinking of trying this ( ZEVN IV ) with a 1738 ( in a Shanling CD Player ) which expects 2.5V at the current output pin.

Just to compare with a Drek conversion i did with Zen-Mod's precious 🙂😎help

I made a mother board for IVs and PSU just so i could test different solutions....here is the chance.
 
#33
Nelson Pass said:
The Zen I/V Converter article is posted here at DIYAudio,
and I am establishing this thread for discussion.

At this moment, it seems to have lost the first diagram, that
of a typical inverting op amp with a virtual ground input,
but I'm sure that will be rectified shortly.

😎
Click to expand...

I have just seen the circuit. 😀

My first thought. Wy did i not come up with that idear! 🙂😡🙂😡

Nelson i am a bit envious! I have to say....

The only thing that bothers me is that the 2sj74 and and 2sk170 is difficult to get you hands on through newark, farnell, mouser and digikey.

But excellent and simple design.


PS: The input will be a virtual ground. Even if the feedback is high impedance.
 
#35

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#36
sonnya said:
Thanks for the info.

I maybe have a little "but".

R5 and C5. Should the not have been feed back to source instead of ground.
I think there is a little drawing failure,
Click to expand...

Sorry i was'nt finished.

I know that you state no feedback and that mades it even more impressive regarding the performance curves. Feedback would rase the performance even more?!?!?! Nelson ?? Am i right or wrong?
 
#37
Hello Mr.Pass,

It is possible to have more detailed measurements for Zen I/V - harmonics levels up to 7th, the contamination spectrum, if possible?

You don't intend to use it for HD signals (such as 24/96 or 24/192) with provided FR, is it correct?
The FR can be adjusted by replacing the filter cap, if necessary, do you have any other samples of FR for different input signals, by any chance?
Thanks!

thanh1973
I am still interested in op amps (less for I/V stage of course), these for example are also op amps HD Audio Opamp
 
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