Changing the sensitivity of manual controls

Posted on Feb 6, 2014

P1 is the manual control of the corresponding parameter (e. g. tune for a VCO, frequency for a VCF, manual gain for a VCA, manual phase shift for a phaser and so on). P1 generates the voltage U1. J1 is the (first) input socket for the external control voltage. P2 is the corresponding attenuator. The slider of P2 outputs the voltage U2. Additional C

Changing the sensitivity of manual controls
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V inputs with our without attenuators may be available (e. g. two or more CV inputs for frequency control for a VCF). The dashed line in the picture is the common point in the circuit where all CV`s are added. The output voltage of the circuit (output of O1) is used to control the corresponding parameter (tune, filter frequency, gain. ) of the module in question. The output voltage is defined by: The relations R3/R1 resp. R3/R2 determine the sensitivity of the corresponding control (P1) resp. input (J1/P2). If for example all resistors are 47k (a common value in the A-100) the sensitivity is 1 for each input. Provided that R3 remains unchanged the resistors R1 and R2 determine the sensitivity of the corresponding control resp. input. Reducing the resistance of R1 resp. R2 increases the sensitivity of the manual control (P1) resp. input (J1/P2). Increasing the resistance of R1 resp. R2 reduces the sensitivity. To modify the sensitivity of a control knob (P1) or CV input (J1/P2) the corresponding resistor R1 resp. R2 simply has to be changed. The audio input circuit for most A-100 modules is similar but the manual control P1 is absent (a DC offset would not make sense for an audio input, audio signals are AC signals). Normally only one audio input is available but there are exceptions (e. g. VCA A-130 and A-131, signal processor A-109). To change the sensitivity of an audio input simply the resistor R2 connected to the slider...

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