module a-137-2 is another version of a wave multiplier. in contrast to the a-137-1 wavemultiplier i the a-137-2 generates four phase-shifted copies of a vco signal applied to the
audio input. the four shifted signals are added to the original signal to obtain a fat sound similar to five independent vcos. the phase shifting is made by a simple circuit that
works only for sloped signals like sawtooth, triangle or sine, but not for rectangles or pulses:
schematics (one unit)
working principle: the audio input signal (typically a sawtooth, triangle or sine wave from a vco) is compared with a slowly varying control voltage (cv shift in). the output of
the comparator is a rectangle wave with variable pulsewidth. when the output of the comparatur is added to the input signal (a sawtooth in the example) with the correct level
relation between both signals one obtains a phase shifted sawtooth. the left picture shows the incoming sawtooth wave on top. the two horizontal dashed lines (blue and orange)
indicate two different comparison levels. below the incoming sawtooth the two resulting comparator outputs (rectangle waves) and the two resulting shifted sawtooth waves are
shown. it is not a "real" phase shift but an algebraic function. but the result is virtually the same. one could obtain the same function even with several comparator modules
a-167 and mixers a-138a/b or polarizing mixers a-138c. but this would require a lot of modules.
the module has available four manual shift controls and four control voltage inputs with attenuators for the four internal shifting circuits. typical sources for these inputs are
lfos, vclfos, random voltages, envelope generators, sequencers or other control voltage sources. internally eight single outputs are available at single pins: the four shifted
signals and in addition four rectangle outputs. a corresponding breakout module with eight sockets is in the planning stage and will be released provided that there are
sufficient inquiries. the original signal and the four shifted signals are equipped with internal jumpers. if external toggle switches are used instead of the jumpers each of the
5 signals can be turned on/off individually.
the audio input is equipped with an attenuator to adjust the level for the right summation of the original and the comparator signals (as described above).
schematics (complete module)
this document shows the positions of the five jumpers and the eight single outputs on the pc board.
for all examples a vco triangle was used as audio source. the four cv inputs were connected to the outputs of a quad lfo a-143-3. the examples differ only in the lfo frequencies
and levels.
to show the basic function we made some more examples with only one of the four shifting stages (i.e. only one shifted copy is added to the incoming signal):
for these examples an sequencer (a-155) was used to generate the cv for both the vco and the lfo. the sine output of the voltage controlled quadrature lfo a-143-9 was connected
to cv shift 1 of the a-137-2. an adsr (a-140) and vca (a-131) was used to texture the boring pure sound. in the first example the sawtooth output of the vco is used, in the
second example the triangle. both examples start with cv shift 1 set to zero. then the level is increased. after a while the manual frequency control of the quadrature lfo
a-149-9 is chanched. in the second example the frequency of the lfo a-143-9 is switched into the audio range at the end of the example.
in the next example the same adsr that controls the vca loudness is used to control the shift too. the second output of the adsr (a-140) is connected to cv shift 1 of the
a-137-2. for clarity again only one shifting stage is used:
the example starts with cv shift 1 set to zero. then the level is increased and decreased again.
this module has a maximum current draw of 30ma. it requires 14 te/hp worth of space to fit in a eurorack frame.
