The long lost 2SK 30(O)

[Tony Allgood]

>There's no difference when substituting 2sk30Y for 2sk30-o in the 303's
vco.

Well, this all depends on luck. The O and Y types are basically the same
FET with a different value of Vp. The value of Vp of each type covers a
range of values. The ranges do not overlap, but it is possible for an O
to sound like a Y if the value of Vp is almost the same. But, it is also
possible for the sound to have an audible difference if the parts are
chosen from the furthest extremes of each range. When I was researching
into the TB303 for the TB3030, I came across many comments that no one
TB303 sounds like another. A lot of people also said that this was some
part of the mystique that goes with the TB303. Bollocks, of course, it
is simple tolerances in the various (cheap) components.

But the square wave sound is affected by this component, although the
sawtooth is not affected audibly. Now it is possible to get your Y to
sound just right, by selecting one with a low Vp. Use a three pin socket
and try them out. See which one sounds OK. It all depends on how fussy
you are.

One wonders why they chose to use O types in the first place if it
didn't make a difference. They could have used the cheaper GR type.

At the time I did quite a few measurements on this, and came to the
simple conclusion that there was a difference, so I settled for using
the original parts. It was easier, but for a time I did in fact you use
selected Y types for O types. Using the selected FETs did make very
little difference, if at all.

But there is another way too, you can alter the value of one of the
resistors in the differentiator leading to the square wave transistor.
Some users of the Syntechno TeeBee have made this a trimmer and altered
this until it sounds right. Check the AH archives on this.

I really need to look at this again. There was a time when I could get
hold of loads of O types, and now it seems that Y types are more common
and I can't be bothered to start selecting again. So I also have a need
for looking into this. And I wonder if I can get the 100 2SK30-GR to
work too.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan