Zen -> Cen -> Sen, evolution of a minimalistic IV Converter

Input impedance of cascoded bf862

Hi!

I am thinking about building a Sen I/V for my buffalo 3 dac using bf862 cascoded with j111 as shown previously in this thread (since I have these transistors already.)

In deciding how many jfet-pairs to use, I have been trying to understand how/if the cascode affects the input impedance of the I/V. Is the impedance of one "pair" the sum of the inverse transconductances of the upper bf862 and j111?

Best regards,
Tor-björn
 
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In deciding how many jfet-pairs to use, I have been trying to understand how/if the cascode affects the input impedance of the I/V. Is the impedance of one "pair" the sum of the inverse transconductances of the upper bf862 and j111?

So after thinking about it I guess this was a quite stupid question.

I'm planning to build a sen as in the attached schematic, but am uncertain about where to use gate stoppers. The "upper" bf862:s will get some, but should there bee stoppers on the lower ones/on the cascodes as well? My google skills fail me, and I have no proper education in electronics (learning by magic smoke as I go along...)
If there is no advice regarding this, I'll just include pads for resistors and jumper them so that I can insert resistors if needed.

Best regards,
Tor-björn
 

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> its going to be a *lot* of work

Why ?
He does not to match a reel (3000).
We match regularly 200 in one go.


Patrick



Oh! You must have an efficient system, what workflow technique do you use? I find putting those little bugs into the template etc. to be very tedious -- and need to match 8 -- but perhaps there is a better way?


I've also found through dumb trial and error that sometimes you don't need gate stoppers and other times you do, can depend reel-reel on the factory the BF862s come from, so use stoppers always.
 
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Hi,
I have a balanced DAC based on 4xPCM1704. Each PCM is responsible for L-, L+. R-, R+. Currently I need unbalanced from balanced signal so I use John Broskie's Unbalancer (as IVconverter).
Also I would like to try and compare IV converter build on discrete components eg (FETs).
Is there any way to adopt (SEN for example) for both halves of the signal eg L-, L+? or maybe I should use two SEN's per channel and make 'desymmetrisation' after that? If so please advice the circuit.
TIA,
bern
 
Hi,
I have a balanced DAC based on 4xPCM1704. Each PCM is responsible for L-, L+. R-, R+. Currently I need unbalanced from balanced signal so I use John Broskie's Unbalancer (as IVconverter).
Also I would like to try and compare IV converter build on discrete components eg (FETs).
Is there any way to adopt (SEN for example) for both halves of the signal eg L-, L+? or maybe I should use two SEN's per channel and make 'desymmetrisation' after that? If so please advice the circuit.
TIA,
bern
IOut of PCM1704 is weak; only max 1.2mA. I thought that I could easy switch my 4xPCM1704 balanced DAC to stereo singe ended.
I can parallel input and output two PCM chips per channel to achive stronger signal (e.g. 2x 1,2mA). Then I could use standard SEN application.
But what about input impedance of SEN. Will it be suitable for parallel connected two PCM per channel?
Regards,
 
One SEN for each PCM1704 for balanced stereo.


Patrick
Thanks, Ofcourse. But temporary I use the single ended amplifier. Maybe in the future I will have fully balanced stereo equipment.

Currently I wonder if I could use two additional PCM1704 chips somehow for stereo using IV CEN/SEN. Do you think that two PCM1704 in parallel as an input for the one SEN stereo channel is good or bad idea?
TIA,