John Curl's Blowtorch preamplifier part II

[john curl]

I stick for the moment to my original position that Cin or Ciss does not change much with Idss, but it certainly changes with device type (geometry and area), especially without a current source load, or cascoded.

 

[john curl]

PMA, for audio you are correct. For RF, maybe it is important.

 

[syn08]

I stick for the moment to my original position that Cin or Ciss does not change much with Idss, but it certainly changes with device type (geometry and area), especially without a current source load, or cascoded.

Problem is, Idss changes with geomentry and area as well. But there, you don't have to admit you are wrong 😀

 

[scott wurcer]

I stick for the moment to my original position that Cin or Ciss does not change much with Idss, but it certainly changes with device type (geometry and area), especially without a current source load, or cascoded.

John you are probably more right than wrong on this and I think the whole issue of cascoding and FET "stacking" in the verticle as well as horizontal direction is under explored. Cascoding with mixed types give a whole range of possibilities.

BTW you have in the past OK'ed slight dynamic forward bias on an open-loop FET stage. Going from -.2V to +.2V Vgs is a huge modulation of Ciss even though there is still no forward current.

 

[gerhard]

If JFETs, don't care about D or S. Makes no difference.

Some are symmetrical (BF862), others are not (BF510-513).

 

[john curl]

Well everyone, I hope that you will now download the datasheet for the 2SK170 from Toshiba. When you have done that, and you have looked at it carefully, we can talk further about this fet, and changes in Idss.

 

[PMA]

Why not 2SK369 ? (369, NOT 389)

http://www.toshiba.com/taec/components2/Datasheet_Sync//53/6937.pdf

 

[jacco vermeulen]

Are they

Hey dude, it was supposed to be educational, right ?

(i could revert back to symmetrical knob posting, you know)

 

[john curl]

It is the same, except magnified by about 2.5.

 

[Magura]

Why not 2SK369 ? (369, NOT 389)

http://www.toshiba.com/taec/components2/Datasheet_Sync//53/6937.pdf

Exactly my point.



Magura 🙂

 

[john curl]

I don't get the point.

 

[Magura]

I don't get the point.

I wanted to know why not to use the 2sk369bl. To me it seems to be the best that (I) have available.


Magura 🙂

 

[john curl]

Either device or even the LSK170 would be OK. They do not appear to change with Idss, as far as input capacitance is concerned. There is NO GRAPH for Cin vs Idss. Please note this.

 

[Steve Eddy]

Hey dude, it was supposed to be educational, right ?

And indeed it was.

(i could revert back to symmetrical knob posting, you know)

I'll pass, thanks. 😀

se

 

[auplater]

drift

Don't quite get the drift here, I certainly am not in the audio industry. The non-DIY aspect to me is "if you can't get X unobtainable part there is no point in proceeding".

simply that Key isn't a high end audio industry equipment wonk, doesn't seem to be trying to learn from the Blowtorch Master, is asking OT questions of the guru in his thread, and then wonders why all the flack...

sort of like a Geddes thread...

that's all

 

[john curl]

Don't build BLOWTORCHES. I have said this, over and over.

 

[Joshua_G]

Don't build BLOWTORCHES. I have said this, over and over.

I wouldn't, I promise!
Anyhow I'm into tubes now, though I may use JFETs at the first stage of MC phono stage, however not Blowtorch and not all SS amp of any kind.

 

[PMA]

I don't get the point.

2SK369 is even better part for audio, than the 2SK170. Higher Gm, Higher Idss, lower noise.

 

[john curl]

Tubes are better.

 

[john curl]

Higher non-linear input capacitance and NO complement. Wake up PMA.