5
a 6.3mm (1/4”) plug to the import jack
and carefully set the gain. The preamplifier
accepts very weak to very hot signals and
features high input impedance (10MOhms)
so that it sounds great with coil and piezo-
electric transducers. It offers a gain of up to
+60dB on the knob plus an optional boost of
+20dB set via jumper
21
on the back (fig.
2). Be aware that at high gain settings the
preamplifier may be sensitive to all kinds of
noises from other devices, switching power
supplies and transformers, as well as hum,
which is often caused by poor shielding of the
input cable.
The envelope follower in Sewastopol is a
unique circuit that offers both rapid reac-
tion to transients and smoothed response
to amplitude fluctuations (fig. 3, 4). As op-
posed to followers based on rectification and
smoothing (which results in lags or unwant-
ed ripples in the output voltage), Sewastopol
makes use of a bipolar peak detector whose
output is held until a subsequent waveform
peak arrives. The response for a rapid in-
crease of amplitude (often associated with
transients) is nearly instantaneous. The
output value may be held for a longer time,
depending on the setting of the env release
knob (fig. 3). During this time the output CV
decays to zero unless there is another peak
or some other component detected (like
noise, or hum, or even an inaudible DC off-
set). If such a component occurs, the follower
will continue updating its output CV as long
as this component remains present (fig. 4).
21
fig. 2
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
5
4
3
2
1
0
-1
-2
-3
-4
-5
fig. 4
envelope follower response
for long release range
V
ms
Long release
Moderate release
Short release
Audio signal
