Doepfer

Oddly enough, the saw waveshaper in this cicuit is my design 
and about the only part that I'm really proud of as it uses only two 
componets, tracks wonderfully across the whole frequency 
range and sounds great (this is what you're hearing with the high 
end fizziness you mentioned). 

As far as the improvements, most of what I did was replace all of 
the 258's wacky discrete components with ICs and modern day 
equivelents.  Buchla used an FET for the initial amplification, I 
used a TLO Op amp.  He had a discrete comparator made from 
a series of NPNs, I used an LM311.  Most significant however is 
that ALL of the semiconductors in the core circuit in the original 
258 are obsolete now and it will cost you about $125 for these 
parts alone if you set off to make one in the 21st century.  I 
replaced all of these with modern day equivelents and in so 
doing, dropped the cost significantly and decreased the 
matching from 5 mv to .3mv (this is a good thing btw as it effects 
the drift).

Luckily, these subs did not change the sound at all.  You see, I 
was building a 258 kit for somebody when I designed this circuit 
and had one here for a sonic reference.

As far as the other additions, I just looked the circuit over added 
things that Buchla omitted originally.  For instance, he didn't have 
a sync input (VERY easy to add).  While he had square out, he 
didn't have PWM.  Without going into details, the way Don made 
the square waves would not allow for PWM. I used the traditional 
method off the triangle core and was amazed at the sound.  Don 
also didn't elect to bring the triangle waveform to the faceplate.  
Given that this is a triangle core VCO, it's VERY easy to do that, 
so I did. 

Another thing - in that all of my waveshapers are first generation 
(all using the triangle as a source), I was able to include a 
waveshape crossfader (which I call morphing) because all of the 
waveshapes are in phase with one another.  Now, I'll admit this 
part doesn't sound like the Buchla method, which sort of 'grew' 
either a ramp of square out of the sine waveshaper circuit, but I 
am happy with my results.  As a point of ference, I used vactrols 
in my crossfader which really smoothes the cross fading out, 
much more so if it was done soley with op amps.

What I tried to do was make a VCO that behaved like a 258 in it's 
reaction to FM (AC) and frequency response to linear VC (DC).  
That part I was able to nail down accurately.  I wasn't concerned 
if the other parts sounded different, because both being triangle 
core I knew they wouldn't be THAT different and they aren't

- Peter