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

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#2,103
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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#2,104
torb said:
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?
Click to expand...

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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#2,110
EUVL said:
> 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
Click to expand...



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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#2,111
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
 
#2,113
bern said:
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
Click to expand...
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,
 
#2,115
EUVL said:
One SEN for each PCM1704 for balanced stereo.


Patrick
Click to expand...
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,
 
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