A proper setting of the release time is crucial
for obtaining a musically useful CV signal
that is not too rough and not too sloppy. The
knob and range switch offer a wide range
of settings suitable for extremely short and
dry transients as well as long tails of reverbs.
While extreme settings are rarely useful in
“normal” applications, they can be creatively
exploited for unusual effects.
When operating on complex music material,
the results may be dominated by the pres-
ence of strong-low frequency components.
If your aim is to detect percussive elements
rather than the bass, set the low end cut
filter to 33Hz to attenuate low frequencies,
or to 3kHz to attenuate low and midrange
frequencies. Keep in mind that removing low
frequencies significantly reduces the overall
amplitude of the follower input.
The comparator block is optimized for gen-
erating note-on-like gate signals and corre-
sponding trigger signals in response to the
presence of sounds at the import jack (and
analyzed by the envelope detector). Please
note that a comparator operating directly
on audio signals would produce a stream of
rapid impulses corresponding to the shape
of the waveform—that’s why the connec-
tion is better left normalled to the envelope
output.
The threshold potentiometer must be care-
fully adjusted to obtain a reliable note de-
tection each time the parameters of the
envelope follower are changed. In order to
minimize erratic multiple firing, the com-
parator is equipped with a narrow hysteresis
circuit. Different thresholds are applied for
increasing and decreasing voltage, so that
any changes within a small range are ig-
nored (fig. 5).
EXchAnGEABLE PrEAmPLifiEr
The preamplifier is located on a separate de-
tachable board (fig. 2) and can be exchanged
with a different circuit, for example a low
impedance, or tube-based preamp. This edi-
tion of Sewastopol ships with a universal
solid-state preamplifier model “877ЛПМБ”,
based on a symmetric JFET input stage and a
very low noise operational amplifier. This pre-
amp model is our best effort to achieve very
high input impedance and gain while keeping
noise at a minimum level. Additional preamp
models may be available in the future. •
6
0
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0
V
ms
fig. 5
hysteresis
Comparator input
(e.g. an envelope)
Normal
threshold
output of a normal comparator
output of a comparator with hysteresis
Hysteresis width
