DOEPFER A-100CGK Betriebsanweisung PDF herunterladen (Seite 21)

User's Guide page 21 DIY Synth Kit

Attenuating signals

In many applications it is necessary to attenuate a signal (e.g. to adjust the ADSR

modulation amount of the VCF or the audio signal input of the VCF). The following simple

circuit is recommend to attenuate a signal:

At the output of this circuit (Uout) appears the attenuated input signal (Uin). A typical value

for the potentiometer is 50…100k. Depending upon the application a linear or logarithmic

potentiometer type can be used. For audio signals usually logarithmic potentiometers and for

CV attenuation linear ones are used. But this is not obligatory. Even for CV attenuation (e.g.

for the VCO or VCF FM) a logarithmic potentiometer may be useful.

Generating manual controlled voltages

For some applications it is necessary to generate a manually controlled voltage (e.g. for VCO

tuning, manual PW control, manual VCF frequency control, initial gain of the VCA). For this a

modified version of the attenuator circuit above is used. The arbitrary input signal Uin is

simply replaced by a fixed voltage:

This circuit generates a voltage in the range 0V…+U. +U can be e.g. +12V or +5V. For VCO

tuning applications +5V is recommended (auxiliary terminal JP8) because this voltage is

independent of possible voltage changes of the +12V supply. ). A typical value for the

potentiometer is 50…100k. Usually a linear potentiometer is used.

Variable resistors

Potentiometers can be used also as variable resistors (e.g. for the ADSR parameters attack,

decay, release or for controlling the slew time of the slew limiter). For this only two terminals

of the potentiometer are used: the center terminal and the CCW or CW terminal. The unused

terminal can be connected to the center terminal. The following circuit is recommend for this

application:

Uvar

U+

Potentiometer as

variable resistor

Uout

Uin

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DOEPFER A-100CGK Betriebsanweisung Seite 21