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Old 3rd March 2009, 05:14 PM   #121
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Quote:
Originally posted by AndrewT
Idss ~10mA.
a little into the BC base.
Therefore ~10.02mA through the Zener.
So there's about 0.5V across the FET. Does that work as a cs with such a low Vds? I'm not a FET man, but seems quite low.

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Old 3rd March 2009, 05:20 PM   #122
Salas is offline Salas  Greece
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I have used this particular JFET taking advantage of 2 things. 1: It's one of the few that can can have lower pinch off voltage than a BJT's VBE. It actually fills the Jung's criteria for double pinch off there too. 2: Many left overs would be available after the matching process for those who made my NJFET open loop simplistic phono. And that simplistic shunt was developed for that phono. As a partner.
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Old 3rd March 2009, 05:25 PM   #123
AndrewT is offline AndrewT  Scotland
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what's the pinch off voltage of a 10mAIdss k170?
what is double that voltage?
add on the 100mV across the 10r.
Does that really meet Walt's criteria?
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Old 3rd March 2009, 05:29 PM   #124
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Yes. That is why I use only 10R. 0.2V pinch off I have measured. Double that and add 0.1V. Also I measure 0.66V from Q3's base to GND. Walt said that is better to have double the pinch off headroom for best noise performance. It would work marginally even, but not best.
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Old 3rd March 2009, 05:35 PM   #125
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This is what we are talking about, right? Vgs=0, Id=10mA. Seems that the Vds is higher than 1V anyway. Or am I missing something?

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Old 3rd March 2009, 05:38 PM   #126
Salas is offline Salas  Greece
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This is common source, not source follower.
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Old 3rd March 2009, 05:38 PM   #127
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Quote:
Originally posted by janneman


So there's about 0.5V across the FET. Does that work as a cs with such a low Vds? I'm not a FET man, but seems quite low.
Yes. For Vds=0.5V a 2SK170 is most likely in the saturation region (where it acts as a CCS). Incipient saturation is defined as the region where Vds>Vp 2SK170 has Vp=-0.2...-1.5V so Vds=0.5V will do.

It is unclear to me though what would be the advantage of this regulator. The loop gain looks pretty small (essentially gm(Q3)*R6~40dB, because the ratio between the dynamic impedances of the zener and the JFET CCS is almost 1) so the line regulation and output impedance are not very good.
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Old 3rd March 2009, 05:44 PM   #128
Salas is offline Salas  Greece
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Its not great. I am no engineer. I just test my DIY ideas. A shunt reg can be surely done technically better.
My criteria, was: Simple, no loop feedback, JFETS and Mosfets, much better sound than battery or LM317.
I did it and met my criteria. Then it has been implemented along my phono by so many people that report it dead silent and great sounding so its ok in my book.
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Old 3rd March 2009, 06:07 PM   #129
syn08 is offline syn08  Canada
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Quote:
Originally posted by salas
Its not great. I am no engineer. I just test my DIY ideas. A shunt reg can be surely done technically better.
My criteria, was: Simple, no loop feedback, JFETS and Mosfets, much better sound than battery or LM317.
I did it and met my criteria. Then it has been implemented along my phono by so many people that report it dead silent and great sounding so its ok in my book.
Well, I got some bad news for you It has negative feedback, and about 40dB! The negative feedback loop is defined by the dynamic impedance of the zener and the impedance of the JFET CCS. The ratio is very small, so the loop gain is essentially the gain of the base amp (Q3) and the whole thing works as a unity gain amp, or Vo~Vz.

BTW, I am sure it sounds great
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Old 3rd March 2009, 06:11 PM   #130
Salas is offline Salas  Greece
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Damn I was expecting that there will be nesting somewhere!

I tried not to define some global feedback loop using op amps with gain etc.
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