Doepfer A-106-1 Xtreme Lowpass/Highpass Filter - Manual (Page 6)

X-treme Filter A-106-1 System A-100 DOEPFER DOEPFER DOEPFER DOEPFER
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modules into the resonance circuit. The standard application
is to insert a VCA for voltage controlled resonance. But even
other modules
- e.g. waveshaper, divider, phaser,
distortion, PLL, wave multiplier, spring reverb, ring
modulator, frequency shifter, BBD or any other audio
processing module - can be inserted to obtain sounds one
has probably never heard before.
On top of this the module is equipped with three frequency
control voltage inputs (CV). One CV input is equipped with a
polarizer. This means that the effect of the external CV (e.g.
envelope from an ADSR generator) to the filter frequency is
positive (+ range) or negative (- range). Especially when the
filter is moved from LP to HP it might be useful to invert the
polarity of the envelope CV. It has to be pointed out that the
frequency response is far away from being 1V/oct but rather
non-linear.
Pay attention that the CV3 and high pass level controls are
polarizers with zero level at the center position. Especially
for the high pass control it is a bit tricky to find the neutral
position. Here are two solutions for this problem:
• Insert an unconnected patch cable or a single 3,5 mm
jack plug into the high pass input (the two terminals of
the plug may even be shortened). For this reason a 30
cm patch cable is added to each A-106-1 module for
free. You may even nip off the jack plug of the cable to
have it available especially for this function.
• Change the high pass polarizer into a normal attenuator
by moving the jumper JP4 to the lower position (see
below)
Pay attention that for pure low pass function of the module
the high pass control "HP level" has to be in the neutral
position or even better a dummy plug is inserted into the
high pass input "HP In".
To obtain the filter section of the original MS20 two A-106-1
have to be patched in series (one in LP mode, the other in
HP mode, both with CL+ and CL- set to zero).
The A-106-1 is far away from being a "perfect" filter in an
academic sense. The control scale is non-linear. With self-
oscillation all sorts of waveforms except sine are generated.
High distortion and resonance settings lead to roaring,
rattling, noise or other unpredictable sounds. High distortion
or audio level may "kill" the resonance at certain settings.
The filter has a significant control voltage feedthrough. The
"band pass" is not a real band pass as a considerable share
of all frequencies passes through. The notch filter does
attenuate only about 50% at the center frequency - and
many more specialties. But the A-106-1 has a lot of
character - much more than any other filter of the A-100. It is
a very strange and awesome filter - somehow quite the
opposite of the 48 dB ladder filter A-108, which is a very
smooth, warm and predictable filter. The A-106-1 is
definitely not the right choice for "moogish" or "civilized"
sounds but for extreme, exceptional and experimental
sounds - this is why we call the module "X-filter", also to