My Take on Threshold NS10

[audiotux]

Yes that is also my favorite ,
the fully J-fet Alephs or X-Alephs .
To get not fully out of topic , maybe also a J-Fet NS 10 !

Jürgen

 

[steenoe]

maybe also a J-Fet NS 10 !

Hmmm, didnt think of that one, but why not?

Steen

 

[steenoe]

maybe also a J-Fet NS 10 !

I think it would be better to give the BoZ or BosoZ a shot with those devices Might turn out pretty good

Steen

 

[tmblack]

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)?

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

 

[lumanauw]

Hi, Tmblack,

Thanks for the advice.

But Q1 is working at around 75 uA and JFET's are noisy with such current.

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?

 

[Zen Mod]

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

Tom

EE

that's my question ,nobody answered ,yet

 

[audiotux]

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

 

[Zen Mod]

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

like this?
without servo and cap connected?

 

[audiotux]

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

 

[steenoe]

Do you have any rule of thumb in what mA should we use a Jfet with a certain IDSS?

Here is some nice articles on Jfet's:
http://www.borbelyaudio.com/special_articles.asp
Check out "The new Frontiers" articles, they tell a lot about biasing J-fets and the use of them.

Steen

 

[lumanauw]

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?

 

[steenoe]

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

 

[tmblack]

I can find no reference to John Curl's remark.
But I would make Id = 1/2 Idss so around 1mA.

This would mean replacing the 10k resistor with 1k ohms.
But insisting on a JFET just increases distortion.

Tom

EE

 

[Zen Mod]

did somebody tried any sort of shunt reg,including "proposal" ?

I'm in a mess of moving from one flat to another house,so-don't count on me at least few weeks.......

 

[lumanauw]

Hi, Tmblack,

Thanks for the info.

But insisting on a JFET just increases distortion.

Maybe you are right. Why NP himself put bipolar for Q1 particularly on NS10. Other preamps like Fet10 use Jfet, but not in NS10? He surely have checked all devices, and he decided to put bipolar for Q1.

 

[lumanauw]

I can find no reference to John Curl's remark.

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.

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

 

[steenoe]

did somebody tried any sort of shunt reg,including "proposal" ?

I intend to build your PSU proposal this week and try it with the new version of the NS10 that I am making. Take your time Choky, but let the PSU cook while moving

Steen

 

[apassgear]

I intend to build your PSU proposal this week and try it with the new version of the NS10 that I am making. Take your time Choky, but let the PSU cook while moving

Steen

Have some simpler ideas for a shunt supply that can also work well on this circuit.

 

[steenoe]

Have some simpler ideas for a shunt supply that can also work well on this circuit.

Tony, could you post one of your nice schematic's? I, for one would like to see what you have in mind

Steen

 

[apassgear]

Tony, could you post one of your nice schematic's? I, for one would like to see what you have in mind

Steen

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.