A-184-2

Voltage Controlled Crossfader / Triangle-to-Sine Waveshaper (Slim Line Series)

Module A-184-2 is the combination of two functions and planned primarily as an expansion module for VCOs or LFOs (e.g. A-110-1, A-110-2, A-145, A-147-2).
Triangle-to-Sine Waveshaper

The upper section is a very precise triangle-to-sine converter (thank's to Tim Stinchcombe who recommended this circuit). It can be used to convert any triangle waveform into a (nearly) perfect sine. The converter is much better than the simple diode converter used in the A-110-1, A-111-1, A-145 and A-147-2. Two trimming potentiometers are used to optimize the sine shape. The converter should be assigned to one VCO or LFO because the trimming potentiometers have to be re-adjusted if the input level or DC offset of the input signal changes. If the trimming potentiometers are deliberately mis-adjusted it can be used also as a waveshaper for non-sine waveforms (e.g. sine-shaped at the top of the signal and a peak at the bottom, even voltage controlled by applying an additional voltage to the waveshaping circuit, "circuit-bending" notes will be available).

Voltage Controlled Crossfader

The lower section is a voltage controlled crossfader. It has two inputs A and B. The two signals are mixed together with variable percentage. When the manual control CF is fully CCW only signal A appears at the CF Out socket. When the manual control CF is fully CW only signal B appears at the CF Out socket. In the center position of the manual control both signal appear with the same level. In addition a control voltage input CV with attenuator is available to enable voltage control of the crossfade.
Two LEDs display the crossfading shares of input A and B.
The crossfader uses two high quality VCAs (SSM2164). Inputs and outputs are DC coupled. Consequently it can be used for audio signals and slowly varying control voltages as well.

The sockets of the upper section (triangle and sine) are normalled to the inputs A and B of the crossfader section. That way the crossfader is used to fade between triangle and sine of the VCO or LFO connected to the waveshaper. If other signals are plugged into the input sockets A and B these signals are used for crossfading.

The main application is to fade between two different waveforms of a VCO or LFO or two different VCF outputs. But the module can be used for any other signals too as the waveshaper and crossfader sections are independent apart from the normalled sockets.

The following document shows the positions and functions of the trimming potentiometers of the module: A184_2_trimming_potentiometers.pdf. "DC OFFSET" is used to adjust the DC offset so that the sine signal is symmetrical with reference to GND. "SINE SHAPE" used to adjust the output waveform to a (nearly) perfect sine. Both trimming potentiometers can be misadjusted deliberately to obtain other waveforms.

http://www.doepfer.de/a1842.htm