Tweaker's Asylum

• Re: Okay, thanks. <nt> - john curl 15:15:53 01/06/02 (1)
  In Reply to: Okay, thanks. posted by groman on January 06, 2002 at 14:32:23:

  Groman, you are making it tough on yourself. If you are using a differential input, then try to find a 2SK389. It is a great matched pair, and I use them by the thousands. I also use them in my $10,000+ preamp, they are that good. They also have a complement, the 2SJ109 that is slightly harder to find, but works well also. Elso and I are not trying to discourage you, but to get you started right. The single devices will be difficult to match. I know because I have designed them into many of my products, before the 2SK389 was available. The 2SK117 is NOT an optimum input part, because it has much lower Gm than the 170 or the 389. It does have slightly higher voltage, but you should not operate it at such high voltages, because it will leak and create noise and offset. However the 2SK117 would be an OK cascode part with a 170 or 1/2 a 389 at the bottom of the cascode. Then you can get up to 70 V operation without too much compromse. You also must be careful about the Idss rating of the devices Most Japanese parts have 3 or 4 ranges. Get the highest range V, if you can or Bl which is the next highest. Gr and Y is OK for portable, miniature apps, but will be harder to to get right. I
  If you can't find the 2SK389 in your one source, do a search on the NET for the part. You should find someone in your area who can help you, or go to Borbeley Audio in Germany. I don't know their exact website location, but it exists.
  
  

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  • It is 6-14mA-117 - groman 17:50:55 01/06/02 (0)
    In Reply to: Re: Okay, thanks. posted by john curl on January 06, 2002 at 15:15:53:

    So I have calculated with 10 mA-devices
    working at about 2-3mA, when doing my calculations
    for either single-stage or diff

    I had the thought about,
    JFET+ bipol low-noise, cascoded foldback,
    at 2+4 mA as input-stage

    in a single-end voltage amp

    current-source from positive voltage
    feeding both that input-stage and a resistor
    connected to 0v, as load
    determining gain together with the emitter resistor

    have to have some solution to how
    to feed that emitter

    this combined with an output-buffer
    of high gain, class A

    But of corse if possible Iwould like to buy
    dual-devices of
    2SK389
    I might do some research about retailers.

    groman
    

    
    
    

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