doepfer a-152 voltage addressed track & hold / switch (multiplexer) / digital outputs price : $175.00

module a152 is a very useful switching and t&h module. it combines a voltage addressed 1-to-8 multiplexer and 8 fold t&h. the active in/output is displayed by a led. the digital output of the currently addressed step outputs "high". the remaining digital outputs are low.

instead of voltage control even clock/reset controlled addressing of the active step is possible. the rising edge of each clock signal causes an advance to the next state. the rising edge of the reset signal resets to step 1.

basis principles: the sum of the voltages coming from the manual address control and the cv input define the currently addressed step of the 3 sub-devices. if the module is controlled by clock and reset the control voltage has to remain unchanged as the cv control has priority over the clock/reset control (e.g. simply turn the cv control fully counterclockwise and do not touch the address control knob).

sub-device #1 is the bidirectional 8-fold multiplexer (kind of an electronical 8-fold rotary switch). bidirectional means that it works into both directions like a mechanical rotary switch: the common socket may work as an output that is connected to one of the 8 inputs that are e.g. connected to modulation or audio sources. but the common socket may even function as input. in this case the signal applied to the common socket is output to the currently addressed single socket. the voltage range of the in/outputs to be switched is the full a-100 voltage range -12v....+12v. all a-100 signals can be switched without any restrictions.

sub-device #2 is the addressed 8-fold t&h. the signal at the common t&h input is connected to the addressed t&h output. as soon as a new output is addressed the last voltage is stored at the output (track&hold function). the t&h section of the a-152 allows the emulation of the "toggling t&h" function of the buchla module 266 "source of uncertainty". only the first two t&h outputs of the a-152 are required for this application.

sub-device #3 is the digital output section. the digital output of the currently addressed turns to "high". all other digital outputs are low. the digital outputs can be used to trigger e.g. envelope generators or to control the reset input in the clocked mode to reduce the number of addressed stages.

remark: in contrast to the sample&hold (see s&h a-148) the output voltage follows (i.e. tracks) to the input voltage as long as the corresponding stage (1...8) is active. just when the stage is deselected the last voltage is held.

the "common t&h input" socket can be normalled by jumpers to the "common switches in/out" socket, i.e. the common t&h input is connected to the common switches in/out socket as long as no plug is inserted to the "common t&h input". this allows a multiplexed t&h, i.e. each t&h output has a separate signal to be sampled.



graphic vco
the picture shows the principle patch for a so-called graphic vco. for a graphic vco the waveform is determined by a sequence of voltage levels. normally the levels are adjusted with faders and the fader positions represent the waveform. in the a-100 such a vco is not available as we believe that the expenditure and costs do not correspond to the result. from our point of view the features of a graphic vco are overestimated very often. but with the a-152 one has the tool to built a graphic vco with a few additional modules only. and that's how it works.

the cv address input of the a-152 is connected to the output of a vco (e.g. sawtooth or triangle output of an a-110 or a-111). the manual address control and the cv attenuator are adjusted so that just all 8 leds of the a-152 light up, i.e. that all 8 stages of the a-152 are addressed while the vco passes through it's waveform (this is why only sawtooth/triangle/sine are suitable waveforms but not rectangle). the cv controlled address generator of the a-152 is able to work up to moderate audio frequencies. if different voltages are applied to the eight multiplexer inputs of the a-152 one obtains a graphic vco signal at the common multiplexer output that has the same frequency as the vco.

here are some examples how to generate the eight voltages:
8 fixed voltages (e.g. from the cv source module a-176: this is the "classic" graphic vco with manually adjustable values (for diy's: 8 faders connected between gnd and +12v could be used too)

8 automatically varying voltages (e.g. 8 lfo outputs from two a-143-3)

8 random analog voltages (e.g. random voltages from a-118 or a-149-1 or s&h a-148)
8 random digital voltages (e.g. a-149-2)

or any combination of the above suggestions

for the last 3 examples the waveform changes more or less accidentally. if the a-149-1 resp. a-149-2 is used the waveform changes can be synced as for these modules the random voltages are triggered by a clock signal. especially in combination with an a-155 a lot of interesting applications may result. e.g. the clock inputs of the a-149-1 can be controlled by the sequencer clock or a a-155 trigger row. in both cases the change to the next waveform is in sync with the sequencer.

if the triangle output of a vco is used to control the a-152 only odd harmonics will occur as the graphic waveform is passed through symmetrically in both directions.

see diagram 1

mono/poly converter
the picture shows an application of the a-152 that distributes a monophonic pitch control voltage (e.g. the cv of a sequencer,  a midi-to-cv interface or a monophonic keyboard) into several polyphonic control voltages that are used to control several vcos. and that's how it works.

the pitch cv is connected to the common input of the t&h unit. the positive transition of the corresponding gate signal indicates that a new cv is generated (e.g. by pressing a key on the keyboard or during the advance to the next sequencer step). the gate signal is used to trigger the advance to the next address of the a-152. the trigger delay connected between the gate source and the clock input of the a-152 is required because of the timing between the positive transition of the gate signal and the cv change. the t&h has to take over and store the cv not before the cv is stable. otherwise the result will not meet the expectations. as the time correlation between the gate transition and the cv change may vary the a-162 is used to solve problems that may arise from this. ideally the gate transition and cv change happens exactly simultaneously, but "simul-taneously" is a problem in the real world as there are always some delays in the micro/millisecond range that may cause problems (e.g. the midi-to-cv interface or sequencer of manufacturer #1 generates the gate transition 200us before the cv change but for manufacturer #2 the behaviour is reverse and the delay is 500 us). to avoid such problems the a-162 is used. first the trigger length is adjusted so that the a-152 triggers correctly. if the width is too short the a-152 may not trigger or the step advances are uneven. after that the delay time is adjusted so that the cv values appear sequentially at the t&h outputs of the a-152 asexpected. usually the a-162 settings will be close to the left-most positions of the controls for delay and length.



in the example the digital output five is connected to the reset input of the a-152 to limit the number of outputs to four.

the four vco outputs can be mixed in an a-138 before the subsequent signal processing (vcf,vca,adsr  ...). but even each vco outputs can be processed separately. in this case the digital outputs of the a-152 may be used to trigger the envelope generators that are assigned to the corresponding vco.

the number of outputs can be decreased or increased by connecting the reset input to another digital output.

a special case is the limitation to two outputs. this leads to the function of the toggling s&h unit of the buchla module 266 source of uncertainty. the only difference is that the buchla module contains two s&h instead of two t&h. if an a-148 s&h is connected between the cv source and the a-152 the functions are identically.

another solution is to modify the a-152 so that the t&h section works as s&h.



7-fold manual ribbon gate
the picture shows an application of the a-152 in combination with the ribbon controller a-198. the position control voltage of the a-198 is used to address the a-152. if the manual address control and the cv attenuator are adjusted in the right way the position sensor of the a-198 covers the complete address range of the a-152 and a small share of the position range is assigned to one of the eight addresses of the a-152.

if the hold switch of the a-198 is set "off" the a-152 jumps to address 1 as soon as the finger is removed from the position sensor. as soon as the sensor is touched, one of the stages in the range 2...8 is addressed and the corresponding digital output turns to "high" - displayed by the corresponding led. this leads to a 7-fold manual gate generator that can be operated like a percussion set. according to the position of the finger, that touches the position sensor of the a-198 one of the gate outputs of the a-152 is active. the gate outputs may be used to trigger percussive sounds stored in an  a-112 sampler module or percussive patches based on other a-100 modules.

in principle the gate outputs can be used for any gate/trigger/clock function in the a-100.

in the example the position cv is also patched to the common t&h input. at the t&h outputs control voltages are available that follow the position cv of the a-198 in a certain range. as soon as the finger leaves the corresponding range the last voltage is stored.

the multiplexer unit can be used for additional switching functions (e.g. to connect different modulation or audio sources to a module).



this module has a maximum current draw of 40ma. it requires 16 te/hp worth of space to fit in a eurorack frame.

to view this module's user manual as a pdf file, please click here.