roland fet

[Tony Allgood]

>roland use a 2SK30 fet which they grade by colour code---gr,y,o,etc.

Not so much of colour but the letter is written on the side of the can.
The parameter that determines grade is the Vp, or pinch off voltage. In
a FET follower circuit, this will affect offset of the output in
comparison to the input voltage. GR is the worst, highest. O is the
lowest that you can get hold of, but there is one lower. Y is the
standard one it seems. There is an overlap between the grades. I have
tested some O types to be worse than Y types.

For a suitable test circuit, your simplest circuit is the FET follower
with the input gate taken to ground. Measure the output voltage across
the source resistor. Make the source resistor quite high, like 100K or
more, and don't forget the DVMs resistance either.

Oh, if you know of a source of 2SK30A-O please tell me, I'm running down
to my last twenty.

Regards,

Tony Allgood  Penrith, Cumbria, UK

Modular synth circuits, TB303 clone and Filter Rack

http://www.techrepairs.freeserve.co.uk/projects.htm