The long lost 2SK 30(O)

[rob]

I did this long ago to compensate for the syntecno teebee which had a
really lame waveform which did not sound hollow at all.. It was some type
of ugly saw/sqr wave..

I used a 250k pot to do it. Linear, log, it doesnt really matter.. Just
tune it till you get what you want out of it and it sounds really springy
and hollow.. The springy sound seems to come from when a high note is hit
(at which time the pulse width changes and the wave becomes nearly
sinusoidal) and then glides to a lower note (where it becomes hollow and
tube-sounding). Sounds like a spring being pulled.. Booooiiing!

Also, too, that pure sinusoidal beeping will not happen properly at high
freqs without the waveshaper tuned properly, or it happens too early.

On the FR-777, although Jared did a great job in his own right, this really
needs to be changed on at least one oscillator to a normal tb303 type
waveshaper to get the proper harmonics and for the filter to react
properly. Also, too, from what I remember, as the freq gets higher, the
amplitude goes down. Instant RMS compression! ;)

FWIW, the 777 has a standard opamp saw generator, and feeding it into the
sqr wave waveshaper of the 303 gave me the same exact waveform and
behavior.

But, OTOH, the nastiness that occurs with the original 303 saw converter
does change the saw sound greatly in relationship to frequency.. I will
have to retrofit this one on there one of these days, but its not as
drastic as the diff between a schmitt trigger waveshaper and a passive
differentiation/filter network like in the 303.

I have messed with about every variable in that circuit, and I can only
find that r35 has the most control over what occurs in that circuit and is
the only useful thing to bother with..

Tuning the pot is strictly up to your ears, frankly... I have even done
mods for ppl where I have left it available to be manipulated and tuned for
whatever particular effect they are after.

Rob




----------
> From: *Star Project <ampe at swipnet.se>
> To: DIY skicka Lista <synth-diy at node12b53.a2000.nl>
> Subject: RE: The long lost 2SK 30(O)
> Date: Thursday, November 16, 2000 3:55 PM
> 
> ok so by trimming R35 one can get the same wave as the O part
> gives with the Y part. Well it could be worth doing this I guess
> rather than hunting down that damn O part. what value should this
> trimmer be anyway? I think I'll start by comparing it to my
> real 303 at first and then turning that trimmer a little more
> to see if I can find something that really turns me on more
> than the original, if there is such a setting.
> 
> Thanks all especially you Trev. Never thanked you for that
> pot and DIN tip. thx
> 
> / Andreas
> 
> -----Ursprungligt meddelande-----
> Från: owner-synth-diy at node12b53.a2000.nl
> [mailto:owner-synth-diy at node12b53.a2000.nl]För Fraser, Colin J
> Skickat: den 16 november 2000 15:56
> Till: 'Trevor Page'; DIY skicka Lista
> Ämne: RE: The long lost 2SK 30(O)
> 
> 
> > -----Original Message-----
> > From: Trevor Page [mailto:trevor at resonance.fsnet.co.uk]
> > Sent: 16 November 2000 11:28
> > To: Fraser, Colin J; *Star Project; DIY skicka Lista
> > Subject: Re: The long lost 2SK 30(O)
> >
> > 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.
> 
> And as Tony said, the component tolerances mean different 303s will
differ
> slightly too.
> My clone is adjusted to sound the same as my real 303.
> Whether it sounds the same as any other is another question.
> 
> It might be worthwhile having a sample of a reference 303 squarewave at a
> given pitch somewhere...
> 
> Colin f
> 
>