Matt said:

have tried to duplicate the 258's functionality using some Asys
VCOs, with their triangle to saw and sine shaping modulation.
The
timbre modulation they offer is very useful. However, I remember
the transitions on the Buchla being very smooth and musical,
with a
much less pronounced change in apparent volume between the
sine and
sawtooths. This may simply be a nostalgic trick of memory, but a
few
surviving tapes from this days seem to bear me out. It seems
like I
have to work harder to get the Asys to respond the way I want
than I
did with the Buchlas

This is due to two things (actually, three):

1) The A. Sys VCO is saw core, not triangle as mentioned in my
previous post

2) The A Sys VCO uses a completely different sine waveshaper
which dramatically effects the sound (the Buchla's are more
pure)

3) I believe that A Sys has a cross fader which goes between the
two. Don's didn't do that. He insread hacked the shite out of his
sine waveshaper circuit to increase/decrease the amount of non
linearity in the diodes which actually morphed the waveform (not
a cross fade of two pure waves). The net result - a wonderful
sine and a saw that looks horrible on a scope, but sounds fine to
the ear. DIY purests though tend to flip their noses up at what
Buchla did here.

Three facts to consider:

1) Don Buchla's designs are odd. Some would argue that hey
weren't design masterpieces and at times reflect the skill level of
a third year EE student. Doesn't make them bad - it (at times)
makes them a little more clumbersome than other would
approach the same circuit

2) Buchla took an outside in approach to design. He defined
operations and then circuits to support those operations.

3) Buchla is probably the most brilliant of all the synth Gods in
regard to pure intellect. Scary smart.