My Take on Threshold NS10

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#184
Ccombination for Q1,Q2,Q3?
Seems the original used high beta transistors, I just used MPSA06/56.
Do you mean for Q2? Q1 have the source (emitor) always floating, following the gate (base)?
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It must be limited by feedback and the capacitors quality.
But Q1 is working at around 75 uA and JFET's are noisy with such current.

Notice JFET's are used in differential pairs and constant current source configuration for linearity.

Any idea what topography was used for the original NS10 RIAA section?

Tom

EE
 
#185
Hi, Tmblack,

Thanks for the advice.😀

But Q1 is working at around 75 uA and JFET's are noisy with such current.
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Aha....This is what I wanted to know. John Curl said that it is not good to use Jfet starving for current. But I don't know what is the minimal threshold for a certain Jfet.

My 2SK30Y has IDSS of 3mA. What is the minimal threshold of this "starving for current"? Do you have any rule of thumb in what mA should we use a Jfet with a certain IDSS?
 
#188
audiotux said:
Hi choky ,
the Phono-Stage is the same as in SL10 MC input
you can see the Phono-Stage on www.passlabs.com/np

Greetings from Germany

Jürgen
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like this?
without servo and cap connected?
 

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#189
yes thats the right schematic
Mr . Pass said on the other thread :
The M1 ( Phono Stage ) remains a unique circuit that no one
seems to have copied , much like the I/V converter on the D1 .
So i think the cap and servo are Part of this circuit .

Jürgen
 
#191
Hi, Steenoe,

Thanks for the link. 😀
In that article it is very clear about how to use Jfet. But I don't find a "rule of thumb" about what is the minimal threshold of "starving for current" in Jfet usage.

Refering to the original NS10 (Nelson Pass') schematic. If I use Jfet for Q1, what is the value for R4? Do you think 10K is too high?
 
#192
I wish I knew😀 I posted the link to those articles, so that someone with more knowledge maybe would say something about it. As far as I understand it, the load resistor R4 and the source resistor R3, must be right to have the Jfet work at the correct point. Maybe Tom has some suggestions?

Steen🙂
 
#196
I can find no reference to John Curl's remark.
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http://www.diyaudio.com/forums/showthread.php?postid=243094#post243094
Marcel, I noted your earlier post. Actually, JFET's can be paralleled with relatively less increase in overall operating current, BECAUSE the transconductance of the JFET's drops as the square root of idle current, rather than directly like a transistor does. This keeps the noise from increasing as fast as you 'starve' the JFET of current. An additional advantage comes from lower internal self heating of the individual JFET's. This improves noise performance, as well.
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http://www.diyaudio.com/forums/showthread.php?postid=270252#post270252
This is complicated. Normally use the highest current to get the lowest noise. If you HAVE to starve the fets, then the GR parts may work best, but the BL parts are actually better operating at nominally higher currents. Run at high current, if possible
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#200
steenoe said:
Tony, could you post one of your nice schematic's? I, for one would like to see what you have in mind🙂

Steen🙂
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This NS10 circuit looks very promising for the use of the precision shunt regulator LM431. I have use these before for the output I/V and buffer on my CD player with excellent result. 😎

The beauty of this compact component (TO-92) is that can be installed right on the gain board and use 2 of these for each channel (one per rail).

I’ll come up with some resistor values and schematic for testing.🙂
 
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