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Has anyone done a Buchla 227 clone?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Has anyone done a Buchla 227 clone?
Mongo1
Hi - I was wondering if anyone had created anything resembling the 227, particularly the spacial distribution section.

I'm considering working on such a project, using SSM2164 quad VCAs to do the distribution, but am trying to figure out how to do the control signals, which have to convert a standard CV into 4 subvoltages.

Any help would be appreciated.

Thanks
Gary
beautyofdecay_
The schematics of the original 227 are here: http://www.synthfool.com/docs/Buchla/Buchla_200/227/
Mongo1
Thanks!

Now if only I can understand it hmmm.....

I noticed that page 3 is missing. I wonder what was on that one....

Gary
divisionbyzero
the newer revs of the 227e use 2164's instead of led/ldr pairs for the quad outputs of each channel.
Mongo1
It looks like the part I'm interested in is on page 1 of that schematic. There's a bunch of circuitry where "X" and "Y" are used in various ways to distribute the signal among the various channels.

What 'X" and "Y" are is elusive though. And what the heck are those FETs doing in there? I think I read somewhere about a way to use FETs to bias an opamp into it's most linear region, but I don't recall the details.

The use of solid state chips instead of Vactrols for the VCAs makes good sense. Vactrols probably didn't impart and special sound quality in that application.

Gary
divisionbyzero
On the 227e X and y are literally the position of the sound in quad space with the origin at left rear (ie at x=0 the sound is hard panned to the left, at vref the sound is hard panned to the right). When swirl is enabled x is the rate of change (at vref/2 the sound doesn't move; at 0v othe sound moves quickly to the left and at vref the sound moves quickly to the right). Y is the radius of the rotation. This is one reason why vactrols are nice in this circuit since doing equal powered panning in two dimensions is much easier with the linearish response of a vactrol instead of the expo response of the 2164 (actually don told me the reason he used them there was because when he designed the 227e there wasn't a quality quad vca available).

Sorry I don't know the specifics about the 227 but I can definitely answer more about the math of doing this (swirl / pan) with a 2164.
sanders
Mongo1 wrote:

What 'X" and "Y" are is elusive though. And what the heck are those FETs doing in there? I think I read somewhere about a way to use FETs to bias an opamp into it's most linear region, but I don't recall the details.


This schematic is repeated 4 times for each quad panning block.

X and Y are the control voltages for x-axis and y-axis panning. I don't know electronics deep enough to really see how this is working-- but I do see the 4016 Quad Bilateral Switch which is gating these two voltages on and off by control of the "assign" pot voltage. It looks like they're then inverted (and scaled?) and sent to the vactrol vcas.

The crazy little 3D graphic at the top represents where (-)x and (-)y voltages are enabled . It says "ext inputs enabled" along one axis, and "assign voltage input" anong the other axis.

Mongo1 wrote:

The use of solid state chips instead of Vactrols for the VCAs makes good sense. Vactrols probably didn't impart and special sound quality in that application.


Vactrols make good sense too, particularly where many VCAs are needed. They make extremely quiet, low parts count amplifiers.
Mongo1
Thanks guys, it's starting to come into focus for me now.
It looks like each of those vactrol stages also acts as an invertor, so you feed -X into one, and it comes out +X on the other side, and THAT signal gets summed into another stage. Damn that's some clever stuff.

One detail - do you know what the little boxes are that have an 'X' inside them on the left side of page 1? They have 3 legs each. Are those multipliers, switches, or ?????

{ actually, it looks like that's probably a CD4016 quad switch }

Thanks
Gary
hakonbraga
Hey Mongo1
did you end up making this project?
If so would you want yo share some schematics or details?
(sooo difficult to read these buchla schem.)
Mongo1
I never did. But there's one at the www.electricmusicstore.com

Gary
diophantine
Mongo1 wrote:
I never did. But there's one at the www.electricmusicstore.com

Gary


I've yet to build mine (have had the boards, panel, and meters for years...), but if you go this route be sure to read this:
https://modularsynthesis.com/roman/buchla227/227si.htm
guitarfool
Google "Sergio Franco Hardware Design of a Real-time Musical System"
I have a downloaded PDF from years ago. It was his Doctoral Thesis long ago IIRC. Goes into detail on the design of a quad mixer/locator.

Roman did a 2164 based version of the Buchla 204 Quad Spatial Director - available at the electric music store. He cheated and used the ATTiny84A to do the control for the 2164's though hihi
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