Doepfer A-137 Handleiding


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doepfer System A - 100 Waveform Multiplier A-137
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1. Introduction Module A-137 is a Voltage Controlled Waveform Mul-
tiplier. The basic idea of a wave multiplier is to multiply
the waveform of an incoming signal (e.g. triangle from
a VCO) within one period. This leads to additional
harmonics. The period and consequently the pitch of
the signals remains unchanged - in contrast to fre-
quency multiplication e.g. with the PLL module A-196.
The A-137 works as a kind of "inverse low pass filter",
i.e. it adds a lot of harmonics to the incoming signal.
Consequently the best results are obtained with signals
that contain none or only a few harmonics (e.g. triangle
or sine waveforms). The A-137 can be used with signals
rich in harmonics too (e.g. saw) but the effect is not as
remarkable as for triangle or sine waves.
The A-137 is a very sophisticated wave multiplier that
offers much more features, more controls and more
waveform manipulations than other wave multipliers
available so far. In addition all four parameters are both
manually adjusted and controlled by external volta-
ges:
• Multiples: number of waveform multiplications
• Harmonics: adds more harmonics similar to the re-
sonance/emphasis control of filters
• Folding Level/Symmetry: value and symmetry of
the upper/lower folding level
A-137 Waveform Multiplier System A - 100 doepfer
2
2. Basic principles
The signal is processed by a standard linear VCA and 4
so-called wave folding stages. The amplification of the
VCA is identical with the Multiples parameter. This is the
working principle of the folding stages: As soon as the
signal goes beyond the upper resp. below the lower
folding level the signal is reflected resp. folded back. The
values for upper and lower folding level are derived from
the input parameters folding level and symmetry. Both
can be adjusted manually and controlled by an external
control voltage (CV). Folding Level determines the di-
stance between the upper and lower folding level, Fol-
ding Symmetry the position of both levels relating to the
zero line. The internal upper and lower folding level are
calculated by adding resp. subtracting the voltages for
Folding Level and Folding Symmetry (refer to fig. 3).
The working principle of one stage by means of a
triangle signal is shown in fig. 1. The upper picture
shows the incoming signal. The areas to be reflected are
filled black. The lower picture shows the output signal of
the stage. In this example the symmetry is slightly posi-
tive and the reflected areas are not symmetrical.
Fig. 2 shows the folding function of three stages. The
amplification (i.e. the Multiples parameter) is increased
for the succeeding pictures to see the effect of incre-
asing Multiples. Stage 4 is not shown because of clear-
ness.
Fig 1: Folding function for one stage
Fig 2: Folding function for three stages
doepfer System A - 100 Waveform Multiplier A-137
3
As the amplification resp. the Multiples parameter in-
creases even the peaks of the folded signal reach the
folding levels of the succeeding stage and the signal is
folded once again as shown in fig. 2. As the module
contains 4 folding stages up to 8 foldings are possible (4
at the upper and 4 at the lower clipping level). Conse-
quently the maximum multiplication factor is 9 (8+1). If a
second A-137 module is added even more multiplicati-
ons are possible.
The Harmonics parameter sharpens the waveform slo-
pes and adds some overshoot at the edges - a little bit
like the resonance resp. emphasis function of a filter.
Internally the harmonics feature is realized by an additio-
nal VCA for each folding stage.
Fig 3 shows the complete schematics of the A-137
module. For each of the four parameters Multiples,
Folding Level, Symmetry and Harmonics a manual con-
trol and an external control voltage input with attenuator
is available.
The external control of each parameter can be realized
with the usual modulation resp. CV sources: LFO,
ADSR, random voltage, MIDI-to-CV, Theremin, ribbon
controller, joy stick, foot controller and so on. Of course
simultaneous control of several parameters with diffe-
rent CV sources is possible (e.g. Multiples controlled by
and ADSR and Harmonics by a LFO).
As the signals within the A-137 are fully DC coupled the
module can be used to process control voltages too.
Fig. 3: Overall view


Product specificaties

Merk: Doepfer
Categorie: Niet gecategoriseerd
Model: A-137

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