Doepfer A-171-2V Eurorack VC Slew Processor Module (Vintage Black)

Manufacturer's description

The Serge Voltage Controlled Slope is a classic design and an integral part of many modular musicians’ systems. The Doepfer A-171-2 is a faithful recreation of the original circuit.

The VCS easily allows one to set different contours for its rise and fall phases. But its non-linear curves are not as extreme as those possible with a module like Make Noise' Maths. Setting times on the VCS is harder, as the useful range is limited to about 20% of the potentiometer’s throw. It’s these differences between these two similar function generators that this modification tackles."

Module A-171-2 is a voltage controlled slew limiter with a lot of additional features beyond a simple slew limiter. It's mostly a licensed copy of Ken Stones VCS which is in turn based on the Serge VCS.

These are the most important features:

• Manual control of the Slew-Up time
• CV control of the Slew-Up time with polarizer
• Switch for linear/exponential shape of the rising section of the response curve
• Manual control of the Slew-Down time
• CV control of the Slew-Down time with polarizer
• Switch for linear/exponential shape of the falling section of the response curve
• Signal input: the "to-be-slewed" signal
• CV Up Input, affected by the CV Up Control and the corresponding exp./lin. switch
• CV Down Input, affected by the CV Down Control and the corresponding exp./lin. switch
• CV Up and CV Down sockets are normalled
• Exponential CV input: named "V/Oct" in the original design but as it's not really exactly 1V/Oct we will name this input probably "exp.CV", mainly used for VCLFO/VCO applications in cycle mode or as common exponential control for both up and down times in slew mode
• Trigger input: used for envelope generation or retrigger in VCLFO/VCO mode, a pulse at the trigger input will start the envelope or retrigger the VCLFO/VCO
• End output: turns high as the output falls below about 20mV, turns low as the outputs goes beyond about 3.5V, in cycle mode a rectangle signal is generated
• Cycle on/off switch: when "on" the End output is internally connected to the Trigger Input to generate cyclic signals like an VCLFO/VCO, max. frequency about 2.5kHz/3.5kHz (shape switches lin./exp.), max period about 15s/40s (shape switches lin./exp.)
• Output: the signal output of the module
• LED display: displays the slew limiter output signal

Typical applications

• VC Slew Limiter / VC Portamento / VC Low Pass Gate
  Cycle switch = off, no trigger signal applied to Trig socket:
  Voltage controlled Slew limiter or portamento generator: the signal applied to the signal input is "slewed". The slew up and down times are controlled manually by means of the Up and Down controls, the effect of the CV Up and CV Down control voltages are controlled by the CV Up and CV Down controls, in exponential mode these controls also affect the slew shape (see symbols at the CCW and CW positions of the controls)
  If an audio signal is applied an short slew rates are chosen the module works as a simple VCF/VCA combo
• A/D Envelope Generator / Pulse Delay / Subharmonic Generator
  Cycle switch = off, trigger signal applied to Trig socket, no input signal:
  Simple Attack/Decay envelope Generator, the rise and fall times are controlled like the slew up/down times above, including the shape of the falling/rising slope of the envelope, the exp. CV input can be used to change both attack and decay simultaneously
  At the End output a pulse appears as the end of the envelope is reached (less than about 20mV), this can be used as a pulse delay
  If a series of triggers are applied to the VCS faster than the total rise and fall times, the module will divide the incoming signal by a whole number. In the audio range the output will be the sub-harmonic series.
• VCLFO / VCO
  Cycle switch = on, no trigger signal applied to Trig socket, no input signal:
  Voltage controlled LFO/VCO, the rise and fall times of the waveform are controlled like the slew up/down times above, including the shape of the falling/rising slope
  the exp. CV input can be used like the CV input of a VCO or VCLFO, the response is exponential but not exactly 1V/oct