Doepfer A-137-1 User Manual

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System A - 100

Waveform Multiplier

A-137

1. Introduction

Module A-137 is a Voltage Controlled Waveform Mul­tiplier. 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 fre­quency multiplication e.g. with the PLL module A-196.
The A-137 works as a kind of "
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

inverse low pass filter

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A-137

Waveform Multiplier

System A - 100

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
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).
stance between the upper and lower folding level, Fol-

ding Symmetry

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 posi­tive and the reflected areas are not symmetrical.

Fig. 2 shows the folding function of three stages. The
amplification (i.e. the
for the succeeding pictures to see the effect of incre­asing Multiples. Stage 4 is not shown because of clear­ness.

the position of both levels relating to the

Folding Level

Multiples

resp. below the

upper

determines the di-

parameter) is increased

lower

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Fig 1: Folding function for one stage

Fig 2: Folding function for three stages

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