The
Original Borg Filter
Inspired by a dream where I was talking to Don Buchla at a party. He was
explaining to me how both the Buchla 292 Lowpass Gate and the Korg MS-20
filters were Sallen-Key designs. I jumped up in the middle of the night
and tested the idea on PSPICE. It worked perfectly and the next day I built
the first prototype on perfboard. This version keeps the three position
switch from the 292. Buchla originally described the design as a "amplitude
and frequency domain modifier". The switch is labeled appropriately
enough "Amplitude - Both - Frequency".= 
+ 
Second
Generation of the Borg Filter with Joystick
By the second version the mode pot had appeared allowing smooth transitions from lowpass to bandpass and highpass. The joystick has center frequency on the vertical axis and peaking (resonance) on the horizontal. The "envelope" input on the back accepts a MoogerFooger control pedal. The unit is powered by two 9 volt batteries and is being used as a "super" waa pedal in the band F/i.
Third
Generation, Now the Dual Borg
Putting resonance on the horizontal axis wasn't as exciting as I thought it would be. You tend to stay in the high resonance area for control, where the filter effect is most pronounced. It seemed like the best effect would be controlling two filters on the two axis of the joystick. This version has independent control of resonance for each section and a series/parallel switch. The middle position of the switch disconnects the two filters and routes them in stereo to the RCA connectors on the back. This proved to be very useful for DJ work and will be reappearing in a later version of the "Space Box".
Back of the Filter
Dual
Borg "Joyrider" filter in Frac-Rac format
I wanted to bring out a Frac-Rac version of the above design. The smaller faceplate made some compromise necessary. The two resonance controls have been combined into a single control for both sections. This is not much of a compromise since you typically use both at the same resonance setting.
Wiard
"Space Box" Dual Filter Dual Oscillator
This is the first of a series of "Electroniums" I am developing along specific themes. This design brings out all the circuitry on the board and is prepatched to make the kind of noises heard in 1950's science fiction movies. Hence "Space Box". The two filters are controlled by one joystick and the two oscillators are controlled by another. The oscillators can be cross-coupled by the "Chaos" controls. Filter 1 can be switched to be a VCA so the vertical axis of the right hand joystick controls the volume.
Faceplate drawing
Side view of the Space Box
Click on picture for a larger view
