Zen I/V Converter

[regal]

Originally Posted by EUVL

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

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

[regal]

If you forgo the coupling caps, the output would be around 0 V DC since this is split supplied. Can't see a reason not to DC servo unless you just happen to have 4 expensive blackgates in your pocket

[nar]

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

[oliverniekamp]

Originally Posted by Zen Mod

there are some funny parts , placed in drains of each jfet ;

they're called resistors , and they're handy for decreasing voltage in appropriate nodes

Hihihi

I could have used my brain...

[regal]

Originally Posted by oliverniekamp

Hihihi

I could have used my brain...

Its fine, I'm using mine trying to figure out a DC servo scheme to eliminate the expensive sound degrading coupling caps. Wish I knew SPICE.


Anyone have a Spice model for this up and running yet ?

[CeeVee]

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.

[regal]

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.

[CeeVee]

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.

[juma]

Originally Posted by regal

.. to eliminate the expensive sound degrading coupling caps....

How about using 0.1uF instead of bulky 10uF? It's possible if the ZEN I/V is loaded by B1 running at approx. +/-10V (it's easy to scale down from +/-30V). Additional benefit is higher drive capability.

[stefanobilliani]

Very nice, loved the D1 for long time . Will try this as soon I will find a nice usb or spdif dac with current output .

Any suggestions ??