Doepfer A-111-2 High End VCO Eurorack Module (MKII)

Module A-111-2 is the successor of the obsolete High End VCO I A-111-1.
Here are the most important features of the module:

• triangle core (i.e. all other waveforms are derived from the triangle by waveshapers)
• fully analog design
• min. 15 octaves pitch range (typ. 0.5Hz - 20kHz in VCO mode / 0.001Hz - 40Hz in LFO mode)
• perfect 1V/octave tracking over min. 10 octaves, typ. 20Hz - 20kHz (control LF has to be fully CW for perfect 1V/octave tracking)
• exponential frequency controls and inputs:
• Tune: range can be selected by means of a jumper, about +/- 1 octave (jumper JP6 not installed) or about +/- 3 octaves (jumper JP6 installed)
• Fine: about +/- 1 semitone range
• Octave: range switch with 6 positions for 6 octaves
• 1V/octave CV input
• XFM input with attenuator
• access to internal bus CV (via jumper, optional, please remove the bus jumper if this feature is not used to avoid unwanted frequency modulation as then the unused CV line of the bus works as a kind of antenna)
• linear frequency controls and inputs:
• LF (manual linear frequency control: fully CW = standard setting for usual VCO applications, fully CCW: close to 0Hz frequency)
• works also as a kind of range control for the exponential section but for standard VCO applications with 1V/octave control voltage the LF control should be fully CW !
• LFM input with attenuator, DC coupled
• Pulsewidth controls and inputs (for rectangle output):
• PW (manual pulsewidth control from 0%/output = fixed at "low" state up to 100% / output fixed at "high" state)
• PWM input with attenuator
• Hard Sync input (CEM3340 hard sync type)
• Soft Sync input
• Waveform outputs:
• Sawtooth, output level ~ 10Vpp (voltage range ~ 0 ... +10V)
• Rectangle (controlled from pulsewidth section), output level ~ 10Vpp (voltage range ~ 0 ... +10V)
• Triangle (output level ~ 10Vpp, voltage range ~ -5V ... +5V)
• Sine (output level ~ 10Vpp, voltage range ~ -5V ... +5V)
• Range switch to select VCO/VCLFO mode, frequency relation between VCO mode and LFO mode about 500 : 1
• dual color LED display (to display low frequencies below ~ 25 Hz)
• Nearly "perfect" waveforms

high end triangle to sine converter with excellent sine waveshape (thank's to Tim Stinchcombe who recommended this circuit)
the micro precision VCO A-111-3 uses the same VCO core as the A-111-2, but has less inputs, outputs and controls
The following document shows the positions and functions of the jumpers and trimming potentiometers of the module: A111_2_trimming_potentiometers_and_jumpers.pdf

Technical remarks:

The control voltage applied to the socket 1V/Oct is added to the control voltage coming from the bus (interruptible by removing the jumper JP4). Connecting a cable to the socket 1V/Oct does not interrupt the bus CV connection ! I.e. the 1V/Oct socket is not normalled to the bus CV. This allows e.g. transposing sequence CV (applied to the socket 1V/Oct) by the bus CV (e.g. connected to the CV output of a Midi-to-CV interface).
The module is based on the CEM3340 circuit. The hard sync of the CEM3340 works different compared to most other VCOs. The excerpt from the data sheet below shows the details. The CEM3340 type of hard sync is also explained in the A-111-1 user manual on page 9: A111_man.pdf.