303 clone filter and VCO not reproducable

[Fraser, Colin J]

> -----Original Message-----
> From: Martin Czech [mailto:martin.czech at intermetall.de]
> Sent: 05 November 1998 12:17
> To: synth-diy at mailhost.bpa.nl; H.J.vanderlinden at stud.far.ruu.nl
> Subject: Re: 303 clone filter and VCO not reproducable
>  
> Ok, lets see if I'm able to get these japanese double tr. also.
> And I also think that the 2x4 ladder tr. are not matched, 
> this would lead
> to difficulties in mass production. This was a cheap instrument!

The transistors in the ladder in my original 303 are *not* the normal NPN
transistors used elsewhere (2SC945), but there is no mention of this on the
schematic. The ladder transistors are 2SC1815.

I used BC182L for all the NPN transistors as Towers list it as a substitute
for both the 2SC945 and 2SC1815. I would guess that Roland must have used
the SC1815 in the ladder for some reason, but I don't know what.

I didn't use the original dual transistors either in my clone - all
transistors were substitutes except for the 2SK30 fets.
For matched pairs of NPNs I used hand matched 2SC2547E. I don't know if
these are a good substitute for the individual transistors in the 2SC2291 or
2SC1583 or not, but they certainly do the job.

> I think that the osc. as such makes only 10% of the sound. Filter
> distortion and/or vca distortion makes 90%, most likely the filter
> allone. And I think that the SCR method is no good idea for a 
> vco at all
> (not stable). 

I used to believe this also, but the 'character' of the 303 oscillator
without any filtering is very noticable, particularly with the square wave -
possibly due to the 'rounding' of the wave from the saw to square convertor.
i noticed the same thing with the oscillator in the SH09 - I replaced the
filter and vca in a 09 with a completely different design, but the character
of the synth is still the same - which IMO must be down to the non-ideal
waveforms from the vco.
I suspect a few Curtis-3340-haters might agree here too ;-)

I would say the 303 oscillator contributes 40% of the sound, the filter 50%
and the distortion in the VCA and elsewhere another 30%.
(120% total due to synergy ;-)


Colin f