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RSF Kobol Expander Waveshaper - kobolws.pdf this is just the waveshaper. it sweeps from triangle to saw to square to pulse. Sort of a combo of the Serge waveshaper that's all over the net with a voltage controlled crossfader. RSF Kobol Expander Sawtooth Oscillator - kobolosc.pdf this is the sawtooth VCO core. the actual Kobol used a 726 matched transistor pair, but since the design is a rip off of the Oberheim SEM anyhow, I just added the SEM exp. converter to the front of the Kobol oscillator and here it is. The one unique part is that RSF swapped the FET buffer with an OP-AMP. There were some minor errors in this, they have been touched up(all of them I hope!!!!). Buchla "Timbre" Waveshaper - buchla_timbre.jpg This is part of the Buchla 259 Complex Waveform Generator. This section takes an ordinary sine wave and gives it rich harmonics. This is like the Serge Wave Multiplier in function, but a quite different implimentation. I haven't built this, but I imagine you could substitute a couple of descrete transistors for the 2N3958. Buchla Lopass Gate - lopass-gate.jpg This is a slight variation on the Buchla 292c quad lopass gate. The actual module had LF13331 switches for the mode control. I have taken that out and replaced it with regular old CMOS analog switches. To use them for analog signals you need to give them +/- 7.5 volts. The power supply is included. I tested this and it works like a charm. This is a later version than is around the net. It uses regular +/- 15 volt power and only easy to find parts. The secret of the lowpass gate is that the "slew" of the Vactrol makes the attack very soft and natural sounding, like a bass guitar. Also, the "both" setting is an imitation of all acoustic sounds. (quiter and darker always together) This is an extremely quiet VCA because there is very little in the signal path. lopass-gate_etch.pdf
Buchla 258 style oscillator - 258mod.jpg This is my own modification of the Buchla 258 oscillator. Since the real 258 used several unobtainable parts, I made an evil crossbreed of the 258 and the Electronotes Option 2 VCO. Unfortunately that means a PNP based exponential converter. The descrete OTA of the original is replaced with a 3080. This is a very cool oscillator. It sweeps, from sine to either saw or square, from voltage. I have tested this circuit with the original 3565 and 4248 transistors as well as regular old 390_ varieties. It works. You may have to mess with values a bit to get nice waveshapes, depending on your FETs. 258etch.pdf ARP Odyssey 2 quadrant modulator - ARPring.gif This is the "ring modulator" in the ARP Odyssey. It is actually just some CMOS gates. It expects a suare wave input from 0-10 volts. This shouldn't be hard to give to it. I think this thing sounds really great, there is no leakage fromt he original frequencies. Source of Uncertainty- I have built several sections of the Buchla Source of Uncertainty all on one circuit board. These include the diode-based noise generator (schematic not shown), "64 levels", random voltage sourse and stored random. I had a problem getting the noise generator to work, but as it turned out it is very importanat that the right zener diode is used;) the "64 levels" is a 4006 shift register that is often used as a noise source, set up to act like a noise and sample and hold. This one works nice at audio rate for video game type sounds. The random voltage source is a vary voltage the you have voltage control of how fast it is moving. use it like an lfo that never repeats. Great for adding unpredictability to ANYTHING. The stored random is a sample and hold with "correlation". It allows you to control how far the next sample can be from the current one. All parts are fantastic, I suggest this project to anyone looking for something new in their cache. storedrandom.jpg Buchla Bandpass Filter- bandpass.jpg The Buchla Music Box does not have a resonant filter. You can use two sections of a lopass gate and a mixer to add feedback and create one. Another solution is to use the bandpass filter. This is not actually the same thing as a resonant lopass, but many of the obtainable sounds are similar. If the bandwidth is narrow, when the frequency is swept, a sounds similar to a resonant filter can be obtained. With a wider bandwidth, the sound of a lopass or hipass can be achieved. The problem with buiding the Buchla 291 Bandpass Filter has always been the odd dual FET that is used as a buffer twice in the design. I have successfully built this modules using both the original obsolete matched FET and using an OP Amp wired as a buffer to replace it. Below you will find the modified schematic and my board layout for a dual bandpass with no 2N3958. 291.pdf Three position toggle switch- 3_pos_switch.jpg When building modules that wil switch modes from a switch, I have often wondered where to get 3 position toggle switches. Sure, you can get ON-OFF-ON types, but that doesn't give 3 distinct inputs to one output. C&K makes a DPDT switch that connects the 2 pairs of terminals on one end in the first "ON" and the other 2 in the last "ON", in the middle it connects one of each. This is a simple schematic, pulled from the Polyfusion envelope follower, for how you can wire that switch type for 3 ins and 1 out or vise versa. Vactrol Crossfader- vac-crossfader.jpg There are times you'll need to crossfade between two sources. One example is to sweep between to waveshapes from an oscillator. This circuit uses Vactrols, eliminating the extra noise of OTA based circuits. There is a similar circuit in the 207 mixer, for the voltage controlled panning. The 207 uses VTL5C3/2 Vactrols with a 47k resistor to ground comming from the center tap and a 10k to ground after the vactrol. This makes a double attenuator, and may give a nicer pan curve with no gap in the middle. That circuit is also below. vac-panner.jpg |
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