[sdiy] WP LM3900 VCF

[Harry Bissell Jr]

The OTA could also be called a "Voltage Controlled Current Source"...
  
  the output is a current, and is the product of the differential input current
  and a bias or control current.
  
  The Norton could be called a "Current Controlled Voltage Source"
  the output is a voltage controlled by the differential input current.
  
  The Norton 'has' some applications that could be replaced by standard
  opamps... most amplifier apps included. These usually have the inputs
  driven by high value resistors (>1M) which essentially make the  input currents subject to the voltage applied to the resistors.
  
  Other apps... especially the ARP four pole filter using the LM3900... are
  using the unique properties of the Norton amp by driving the inputs with
  a current source.  These cannot be duplicated with standard opamps (without
  great complexity).
  
  The Norton is an odd duck. Misunderstood in its infancy, it got a reputation
  (not wholely undererved) for being a "piece of sh!t"  (opinions of many respected
  engineers).  Other designers such as Serge T.  (YOU spell his last name then...)
  excelled with the part.
  
  H^) harry

Johannes Öberg <johannes.oberg at gmail.com> wrote:Thanks!  However, my problem is not finding datasheets, I read the 3900  datasheet before my first post in the thread. (well, 'looked at' is the  more accurate verb considering I didn't really understand the  schematics...)
  
The problem is that I don't understand electronics very well, and I  can't really "get a feeling" for Norton amps. While I could just about  tell an emperor Norton amp from a hole in the ground, I would have no  clue if I would try to replace a normal opamp with a norton in a  circuit, something datasheets talks about.  

I was hoping that perhaps somebody had some sort of simple  explaination or some metaphore or something, that would make me "get  it". Datasheet language isn't very pedagogic (and why should it be?). I  have found excellent tutorials online on many sdiy subjects, but I  haven't found any about Norton amps.  

Btw, is the Norton amp a sort of reversed OTA? And that is its use in VC stuff?

/J

On 1/13/06, Rönnberg Niklas <  nikro at itn.liu.se> wrote:  I'm not sure what datasheet you want... but here are some
http://www.alldatasheet.com/view.jsp?Searchword=LM3  
  http://www.synthdiy.com/show/showproduct.asp?show=1219
Hope this will help!
Regards
/Niklas

    

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