Manual

DOEPFER System A-100 Synthesizer Voice A-111-5
15
12 VCA Amplitude (Manual Gain)
13a VCA AM Source Switch
13b VCA AM Level
This group of elements is responsible for the amplitude or
loudness of the Voltage Controlled Amplifier (VCA).
Amplitude control 12 is used to adjust the loudness of the
VCA from zero to maximum manually. In other synthesizers
this control is sometimes called "initial gain". If the VCA is
controlled by the ADSR this control is usually set to zero.
Otherwise a tone will be heard permanently because the
ADSR generates a positive control voltage. If the VCA is
controlled by the LFO this control may be set to a medium
value as the LFO signal is bipolar (i.e. positive and negative
voltages are generated).
The VCA used in the A-111-5 has a very special control
scale that has an exponential behaviour in the range from
about -20dB to –80dB and a linear scale from about -20dB
to 0dB. This scale results in a loudness behaviour that is a
bit different from pure linear or exponential VCAs.
Switch 13a and control 13b are responsible for the
amplitude modulation (AM) of the VCA. Switch
13a is used to select the AM source:
upper position: LFO1 = AM source
center position: no internal AM
lower position: ADSR = AM source
Control 13b is used to adjust the intensity of the internal
amplitude modulation.
In addition to the internally generated amplitude of the VCA
the control voltage applied to the "VCA A" socket
4 modulates the amplitude of the VCA as described in
chapter 3.
Remark
: The amplitude range of the VCA is 0...1, i.e. the
maximum amplification is limited to 1 (though that's not a
"real" amplification we use the same terms as usual for
synthesizers). The full range is covered by the manual
amplitude control 12 . If the sum of the manual setting and
the added modulation (internal or external) exceeds the CV
that corresponds to amplification 1 kind of "control voltage
clipping" occurs. Even with the internal LFO and ADSR
clipping is possible if control 13b is fully CW. To obtain a
VCA loudness contour without CV clipping control 13b
should not be set to maximum unless this behaviour is
intended. The following picture shows the effect of CV
clipping on the basis of a triangle LFO signal:
This behaviour was introduced intentionally as it leads to
additional "trapezoid" or "clipped ADSR" loudness contours
not available without clipping !
CV for
amplification 1