Buchla systems use stacking banana cables for patching control voltages and Tini-Jax cables for audio. In the 200t Tiptop Audio’s Stackcables are used for both signals.
In the Buchla world, audio jacks have metal nuts and CV/Gate are colored banana nuts. In the 200t that aesthetic look is maintained, but since the 200t takes advantage of shielded audio jack and Tiptop Audio Stackcables, that isolation of audio and control signal is no longer needed. Patching audio and CV/gate to each other is now possible adding a world of cross patching not originally available on these modules.
One important specification to note though is that the Buchla control inputs have a range of 0 to +10 volts but the audio signals only go to +5 and -5 volts, so when an audio signal is patched into a CV in it will sweep only half the range. For example, using the audio output of the 258 VCO into the CV stage addressing input of the 245 sequencer will only address stages 1-3. Using an amplifier or offset module like the 257 can change the range to cover 0 to +10V.
The 200t modules work best driving CV/Gate/Audio inputs of around 100kOhm. Output resistance is typically in the 499-1kOhm range.
From time to time we will add optional modifications here.
Modifying the colored switch caps: Switch caps are made using hot air blowing technique. It’s a very old production technology and results in large tolerances. At the factory we sort them however if you feel your cap might be too long, you can pull it out, compare it to the toggle switch shaft and if it is longer than the shaft you can cut it to better match the shaft size.
The original Buchla 200 modules were designed for low quantity hand built production. The 200t is produced with modern processes and with that tolerance control comes into play. Some of those tolerances are addressed on the factory floor using hand measured components and some using the on board trimmers. For VCOs we do not suggest changing the 1V/Oct trimmers as they were calibrated using high precision instruments. Other trimmers can be adjusted and their functionality is described in each module user manual.
The 200t series integrates original Buchla standards into Eurorack. CV Gate and Triggers are standard Buchla 0-10V levels.
Audio output of VCOs can range 8-11Vp.p which is around the typical 10Vp.p Eurorack levels. Note that audio signals are bipolar, a 10Vp.p wave means -5V to +5V.
The VCOs have a standard Eurorack 1V/oct input for pitch control.
One important specification to note is that in the original Buchla 200 CV/Gate and Audio are separated and cannot be cross patched. In the 200t they can, but be aware of the voltage differences between the two. More on that in the Patch Cable section.
Below are part numbers for some of the parts that might wear over time. Online shops like mouser.com carry them.
Momentary white push switches (281/245): TL2230OAF140
Latching white push switches (257/292): TL2230EEF140
Two position toggle switch: 200MSP1T1B2M2QE
Three position toggle switch: 200MSP3T1B2M2RE
FAQ & Troubleshoot
Q: In cycle mode at audio rate generator 1 and 2 and generator 3 and 4 could affect each other’s pitch slightly, is that normal?
A: Yes that is normal and is due to the internal connection between 1&2 and 3&4. Also note that the 281 is not designed to be an audio VCO and does not have typical VCO circuits like temperature compensation or linear pitch tracking.
Q: I noticed that the 281 does not work with one of my passive “LPG” Eurorack modules but does with other types of module, why is that?
A: Passive “LPG” designs short the output of the 281t and it cannot drive the circuit. This places tons of stress on the output circuit of any module and these passive “LPGs” should be avoided
Q: Why are there transistor parts on the back PCB that do not have components installed?
A: These parts allow us to swap between versions of transistors based on part availability
Q: Is the control FM linear? What about the audio input FM?
A: The control FM (black nut) is logarithmic response. The audio FM (metal nut) is linear FM