Teardown of the Buchla 261e Complex Waveform Generator: PCB Analysis

[TheTrashcutter]

happy new year ! - non-covered led<->LDR only makes some switching function?

[DrJRK]

I've seen a pic with those boxes open a LONG time ago, so I can't quite remember how they were set up. However, those boxes appear to be a bit big for a single vactrol setup. It's possible that they contain something akin to VTL5C3/2 or full dual perhaps.

I was never quite sure why the other two were left open, unless it was for a bit of cross dependence or somewhat random behavior. Even sealed factory VTL vactrols can pick up a bit of light under a lamp, so those have to pick up quite a bit. Possible power LEDs, leakage between module panels, etc. Perhaps it's to mix in just a touch of random "analog" style behavior in some aspect of the VCO.

[ghostexits]

Love these 200e tear downs. Hoping you’ll get an opportunity to impulse buy a 297 Infinite Phase.

[AnalogDude_]

Hey professor, i would like to know how the circuit in the 259 that comes before the "timbre circuit" on the shame sheet works, i think it's the symmetry circuit and could it be replaced in solid state form, don't have the dual vactrols. it has a ground connection between the 2 resistors in the vactrol.

I'm have currently a microchip MCP4922 12 BIT DAC on the breadboard with the Microchip Fubarino, the DAC is rated up to 20MHZ.
4096 (DAC) steps x 20 kHz = 81920000, a bit more than 80 MHz, to draw a SAW wave, right or wrong?
How it's done?

[johnmeroney]

I have some understanding of qualities imparted by vactrols in the 292e, as I can hear differences in the four channels of mine. What functions do vactrols serve on the 261e. Is it part of the waveshaping upper right section? I know the osc is a digital sine wave so I’m curious if that is using it after the DAC process

[skriptico]

that build is a thing of beauty :O una bellezza per cosí dire.