Doefperions -

258/259 - whaddya want to know

I've built a Buchla 258 kit and passed on a 259 kit once seeing
the how much work envolved, but I am intimately familiar with
both of them.

There's a few things about these guys which make them unique
- they have triangle wave cores. This means the basic engine of
the circuit creates a triangle wave, as opposed to a saw wave
that most VCOs out there work from, including the Doepfers.
Other VCOs which incorporate a triangle core are Wiard and
Aries.

What a trui core affords you is a completely different reaction to
AC FM (and PWM if you care to doo that, which Buchla didn't)
than almost anything out there, which is one of the personality
traits ofthe Buchla VCOs. The FM is really really warm.

The 258 and 259 have basically the same engine, although
Buchla replaced many of the discrete parts in the 258 with ICs in
the 259. Not to worry, most of these parts are not 'sounding' -
(not in the audio path), but functions such as the internal reset,
which on the 258 is done with a bunch of matched transistors
(begs the question of 'why'), were rightly done with a LM311
comparator in the 259.

Another difference (actually, a big one) was the selection of
what's called an expodential converter in the 259. In the 258,
Don used the infamous UA726 IC, an absolete part also used in
the rev 2 Minimoog VCOs which would set you back upwards to
$150 A PIECE if you needed to replace one today. Don used
another part for the 259, also obsolete now but easily sub'd (not
so with e UA726) but because of this difference, the 259 FM
does not sound the same in the 259 - and it's my opinion that the
258 sounded better. Let it be known, from personal experience
the Buchla 258 expo circuit conventions can be duplicated with
modern day components - but it's a trade secret (mine) and I'm
not tellin!!!

Another unique quality of the Buchla VCOs is the sine
waveshaper. Not a Buchla design (although he did some major
hacking with it), but one borrowed from an article published in
Electronics Magazine in the mid 60's which also later appeared
in the first edition of electronotes. It intentionally overdrives two
diodes to bring them into nonlinearity and produces one of the
sweetest sines out there. Dieter, if your listening - this too would
be an absolute requirement if your intention was to make a VCO
which behaved like Buchla's. For my buck, this is arguably
better than the Thomas Henry tri to sine converter circuit, largely
held as the best out there.

This is where the simularities of the 258 and 259 end. The 259
had with it a very complex waveshaper and a modulation VCO.

They are GREAT VCOs - both of them. They don't track worth
shite, but remember, the Buchla was not considered a
performance instrument as much as a studio instrument, so
periodic tuning was not as much as an issue.

Let it also be known that there's a way to fix this, too...but I
reserve this also as my trade secret!

OK OK OK - I've done a VCO which while not a clone of the 258
by any means, sounds pretty much identical on all counts and
does things it didn't (both hard and soft sync, PWM, a triangle
output and selectable wavemorphing among other things) and
it's much more stable. I am contimplating bringing it to market.
although the jury is still hung on this one. I have two made now,
both in Doepfer size configuration to fit my system, with a couple
more to come in the next few months (i'm having PCBs designed
now).

hope this helps,

Peter