Ken Stone/1973 classic Serge/Serge filter

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The following info on the 1973 variant of the Serge filter module is presented for educational/historic purposes only and are not to scale.


PCB pattern

The component side photo is not of Ken's unit, but of a similar but later model. The values are taken from his version of the module where readable. Some values have been taken from the board in the photo, where they generally seemed to agree with the little that remained of the components. Some values have been taken off the web schematic. Why? Because the unit was encased in resin that failed to cure properly. The result was the ink vanished off many components, resistor bodies dissolved etc. No wonder it didn't work!

PCB connections

  • A = input (via level pot)
  • B = High pass out
  • C = Band pass out
  • D = Low pass out
  • E = VC
  • F = Subsonic switch connection
  • G = Subsonic switch connection
  • H = Q Pot wiper
  • I = Q Pot CW
  • J = ?
  • K = ? (round pad)
  • L = ? (round pad)
  • U = Q Pot CCW. Level pot CCW
  • W = 0v
  • X = +12v
  • Z = -12v


The transistors are proving to be difficult to identify due to the resin on the boards erasing much of the text. I'm pretty sure on the 2N4248s (2N4__8, 2N424_, __4248, _____). The FETs are a different matter. The metal can FETs in the photo apparently have "FN1927 7012" written on them. Mine are white bodied with black epoxy caps and one reads something like "ITF4340 (symbol) 7206" (ITE4340??). The other is blank. Most likely the last 4 digits of each is the manufacture date. I have no data on anything with those numbers (or obvious derivatives 2N1927 etc).


Readers are permitted to construct these circuits for their own personal use only. Serge Tcherepnin retains all rights to his work.

See also


External links