The long lost 2SK 30(O)

[Trevor Page]

I guess it is down to luck. I must have been fortunate to get a batch of -Y variants which happened to make a good substitute for the -O! I used -Y's in my TB3030's and got good results, i.e. producing squarewaves of the correct pulsewidth. Placing a trimmer in the differentiator circuit is a good idea. I stuck a trimmer in place of R35 and then managed to get several JFETs to work. Trim for a nice 50% duty cycle, but remember this varies with frequency anyway.


----- Original Message -----
From: "Fraser, Colin J" <colin.fraser at calanais.com>
To: "'Trevor Page'" <trevor at resonance.fsnet.co.uk>, *Star Project <ampe at swipnet.se>, DIY skicka Lista <synth-diy at node12b53.a2000.nl>
Sent: Thu, 16 Nov 2000 10:02:33 +0000 (GMT)
Subject: RE: The long lost 2SK 30(O)

> > -----Original Message-----
> > From: Trevor Page [mailto:trevor at resonance.fsnet.co.uk]
> > Sent: 16 November 2000 08:43
> > To: *Star Project; DIY skicka Lista
> > Subject: Re: The long lost 2SK 30(O)
> > 
> > A 2SK30-Y will be fine. There's no difference when 
> > substituting 2sk30Y for 2sk30-o in the 303's vco. Use a 
> > 2SK30-Y. Please don't go searching for the -O version, 
> > there's simply no point! 
> > 
> > Most JFETs with a suitably low Vgs(off) should work and 
> > you'll not detect any difference. For my own 303 clone I'm 
> > using a modern device that's much easier to get hold of. It 
> > has a pinchoff of about 1.5V. 
> 
> I found the characteristics of the FET buffer in the vco will make a
> difference to the width (and sound) of the square wave, due to the
> interaction with the square wave convertor.
> I added a trimmer to my clone that allows me to compensate for this, and
> once I set up the clone vco to match the pulse width of my real 303, it was
> indistinguishable.
> Can't remember the resistor number off-hand I replaced - it's in the square
> wave convertor.
> I check it out tonight if you're interested.
> 
> This only affects the sound of the square wave - I didn't hear any
> difference in the sawtooth.
> 
> Colin f




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