L.E.P - Arpopone (Eurorack)

The Arpopone is a bass line generator with a rhythmic chord section. It is based on analog ramp dividers which can be found more than ten times in this design. For the melody generation there are two arpeggiators, which can go up or down and offer a variable step count. The bass features its own resonant low pass filter and envelope. Bass and chords can be mixed with separate level controls and summed at the stereo output. The Arpopone offers a lot of functions in a small footprint and invites for experimentation! A synth-voice for sound pirates!

The Arpopone from LepLoop is a little synth-voice for generating a melody or bass line and a chord section at the same time. It is based on analog ramp dividers of which each one generates a voltage ramp starting from a master clock that can be internal or external.

Trig1 and Trig2 potentiometers set the number of clock pulses.

With the Trig Mix switch it is possible to select between a single trigger (1 or 2) or both (1+2) to advance the scales.

The Scale Step potentiometer sets the number of steps for the two scale generators.
In the mixer section, the two scales are summed together to obtain a more complex pattern. The amount of each scale can be set by two controls and can be positive (ascending scale) or negative (descending scale).

With the VCO Pitch knob, the melody can be transposed while maintaining the same interval between notes.

The note generated by the VCO is fed to a chain of dividers to obtain four sub harmonics of the original note. One of these is the bass section with its own filter and envelope, the other three form the chord section with their envelope.

The two envelope sections are identical, both have a selector for different trigger sources:

• Trig1 & Trig2: the envelope starts at the flash of the green LED (bass) or yellow LED (chord)
• SB1 & SB2: the envelope starts at the first step of  Scale1 (bass) or Scale2 (chord)
• White & Blue:  the envelope follows the intensity of the white LED (bass) or the blue LED (chord). Except for this setting the envelope length is set by the two controls Bass ENV and Chord ENV. Additionally, an EXT CV input allows to provide an external envelope.

The bass channel is passed through a resonant low-pass filter with Cutoff and Resonance control.

Finally the Bass and Chord channels are mixed together. The output level is set by the Bass LEV and Chord LEV controls.