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![Buchla Module](C:buchla_doc/static/img/200e/257e.jpg "Buchla 257e”)

The Buchla 257e

Control Voltage Processor​

The Buchla 256e is a module that offers two types of control voltage processing.

The first section is comprised of two identical versions of a powerful control voltage processing tool. Each of the two sections provides control voltage selection, multiplication, addition, scaling, inversion, and non-linear transformation, all in a simple, immediate, and visually-clear manner.

The second section is comprised of three identical versions a full-featured control voltage slew processor.

Voltage Processor Input and Output​

Each of the two voltage processors has a voltage control input and output labeled with the channel it is associated with. Input is a black banana jack, output is a blue banana jack.

The "Transfer Function" Screen​

This screen allows you to discern the settings for the "Output @ 0 Volts In," the "Output @ 10 Volts In," and the breakpoint settings.

"Output @ 0 Volts In," and "Output @ 10 Volts In"​

At default, the 0 Volts In knob is at zero, and the 10 Volts In knob is turned all the way up. This setting represents the situation where the input is as it is. If you set the 0 Volts to 10 and the 10 Volts to zero, the input signal is fully inverted. Setting these at various settings between zero and 10 will allow you to scale and shape your control voltages.

Breakpoint​

Since the relationship between the "0 Volts" dot and the "10 volts" dot on the screen can be described as "a line connecting them," the Breakpoint function allows you to create a more interesting voltage shapes that create more complex outcomes.

The Breakpoints are in a section beneath both the A processor and B processor, but are labeled "A" and "B" so that you can tell which breakpoint goes with which processor channel.

If you press the "Breakpoint" button, another dot appears between the 0 Volts dot and the 10 Volts dot, creating a more complex interpolated shape. Using the "in value" and "out value" knobs, you can place the breakpoint dot anywhere in the grid of LEDs between the 0 Volts dot and the 10 Volts dot, allowing you to control the behavior of the voltage. The "in value" knob moves the dot left and right, and the "out value" knob moves the dot up and down.

The breakpoint-related knobs are disabled when a breakpoint is not present.

##The Matrix While the matrix of LEDs is somewhat coarse, the actual voltages in the 256e are calculated to a high degree of precision; such that they can be applied to pitch and other applications requiring a level of accuracy.

Control Voltage Slew​

The "slew rate" is the rate of change in a control voltage. By changing the rate of change, you can get everything from altered waveforms to smoothed abrupt changes to portamento.

Channels C through H allow the adjustment of the slew rate of input control voltages. The inputs and outputs are independent, but the slew control functions are shared in pairs in each of the three sections.

In each of the three sections of dual slew processing, the black banana jacks are inputs, the grey banana inputs are independent inputs for the negative slew and positive slew of each section, the red banana jacks are pulse outputs, and the blue banana jacks are control voltage outputs.

How to Slew​

The "Neg/slew" knob controls how much slew, or delay in voltage change, is applied to the voltages moving in a negative direction. The "Pos/slew" knob controls how much slew is applied to voltages moving in a positive direction.

A square wave serves well as an example, as its shape takes almost no time to go in a positive and a negative direction. Its "sides" are straight up and down. Since the slew delays abrupt changes, one can quickly see and hear the way that the slew changes the square wave. Adjusting the "Neg/slew" knob would make the square wave's straight-up-and-down right side into a slope. Adjusting the "Pos/slew" would make the square wave's straight-up-and-down left side into a slope.

Slew Automation​

The grey banana jacks marked "Slew CVs" serve the purpose of using control voltage to turn the "Neg/slew" and "Pos/slew" knobs, as shown by the arrows on the face of the module. For the greatest control, the "Neg/slew" and "Pos/slew" knobs should be turned fully to the left. If they are turned fully to the right, control voltage input to the grey banana jacks will have no effect.

Rate/Time/Auto-Pulse Enable button​

There is a grey button at the bottom center of each section which serves two purposes; to select "rate" or "time" as the section's slew response to the input voltage control, and the activation of "auto-pulse."

"Rate" and "Time" respond to input voltages slightly differently. Put simply, "rate" will give you a wider CV range of response, and "time" will give you a smoother response.

Holding the grey button for two seconds will enable "auto-pulse." The red LED will light, and Auto-Pulse will output a pulse from the pulse banana jack whenever the voltage reverses direction. Auto-Pulse can be disabled by holding the button for two seconds again.

Note: to get a consistent pulse output based on the input CV direction reversal, turn the slew rate knobs down so that slew has minimal effect. Auto-pulse may be less reliable if the slew rates are long, or above 35Hz, or if the range of the input is limited.

Preset Management and Remote Enable​

Knob and breakpoint values can be stored locally and later recalled when a preset is generated with the Preset Manager.

To connect or disconnect this module from the central library function, press "rem enable." A lit LED indicates that the module is connected.