TB303 part 3

[Tony Allgood]

Hi all,

Well I have found a 2SK30A(O), as the FET follower, really does make a
difference to the output of the bassline's VCO. Using a 2N3819 created a
totally different waveform because of the high Vgs(on). I guess people
who have used this part, and similar others, and liked the output of
their VCO, just got lucky. My bets are that the 2SK30 comes in different
flavours... marked up by the manufacturer in terms of Vgs(on). The one
in the VCO are O, but the one in the EG is a Y. Fortunately the one I
ripped out of an old RMK100 was also the O part. The follower now
follows extremely well in my VCO. I would say that the flat on the saw
waveform is solely down to the FET and not the SCR at all. Which would
also go to explain why some TBs sound better than others, since Vgs
cannot be classified that accurately. And don't forget that the follower
will have a knock on effect on the mark space ratio of the square wave.
I checked up some data on 2SK30, actually a spice model, it seems that
Vgs(on) is between 0.2 and 3 volts. This is somewhat lower than the
commoner parts. RF devices do seem to have this sort of value, but these
can be quite pricey. However, the 2SK30 does appear to be a RF device in
many lists, rather than a common or garden audio type.

Does anyone have any datasheets on the 2SK30?? I am guessing pin out at
the moment.

Regards,

Tony Allgood, Cumbria, UK

e-mail: oakley at techrepairs.freeserve.co.uk

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