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design — construction — sound

Eurorack Module


Dual Precision Adder/Comparator and Voltage Source

The new version of the Add1 module contains two independent precision adders, with respective different functionalities. The provided basic functions and its versality – suitable both for audio and/or CV applications – makes this module to an useful part of any synthesizer equipment. The 1st circuit (upper one on the panel) consists of an adder with 3 inputs, whereby the 3rd input is equipped with a polarizing level knob for attenuation, slightly amplification and inversion of this input channel. The sum output has a switch for determing the amplification factor (between *0,5, *1,0 or *2,0); an additional red led indicates if the output signal is becoming overdriven. The 2nd (lower circuit on the panel) has two inputs and an addable voltage source with an amount control knob (level adjustable from 0 – 5V) and inversion/zeroing switch. The output is switchable between sum and comparator mode. In sum mode, it will provide the additioned sum of the two inputs and the generated voltage from the voltage source. In ‚Comp‘ mode, the circuit is working as a comparator with a slightly schmitt-trigger-like characteristic. This mode has only two states, low and high (depending on the threshold level), suitable as gate/trigger, squarewave/pulse audio signal etc.. The threshold level is ≈0V, but it can be shifted by using the internal voltage source or by an external signal. An yellow led is indicating the ‘high’ state; or in sum mode, the clipping of the output signal.

red (dotted): Input; grey: output in comparator mode

Add1 front view
frontal view
  • Audio sub-mixing
  • High precision CV signal mixing
  • Addition, substraction, offset control
  • Attenuation, amplification, inversion
  • Adjustable voltage source (polarity switchable)
  • Comparator mode (with logic level output)
  • Signal-to-squarewave/trigger/gate conversion
  • LEDs for visual control
  • Also available in banana version
  • Eurorack module
  • Width: 6 HP
  • Dimensions: 128,5 mm x 30,2 mm
  • Depth: 30mm
  • Supply voltage: ±12V
  • Power consumption: ≈ 10-20mA

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Add1 panel drawing
Add1 right side view
Side view right
Add1 side view left
Side view left
Add1 banana version
Banana version


Example Addition

Addition ▲▼(both adders)

Addition of two signals; Sum signal is provided on the output:
Voltages In1 + In2 = Output voltage

▲ 1st adder: Inputs 1+2 ; Switch ‚∑-Amplification Factor‘ = 1,00 or ▼ 2nd adder: Inputs 1+2 ; Switch in upper position ‚∑’

Comparison Adding-Comparator Mode

▼ Comparison between adding and comparator mode

Output waveforms of  2nd circuit (▼)  with two triangle signals applied on Inputs In1+In2:
  • Switch in upper position  (addition) (Yellow LEDis indicating voltage on limit)
  • Switch in lower position (comparator (Yellow LED is indicating comparator state ‘high’)
Pulse width modulation

▼ Pulse width modulation

The comparator can be used to convert any signal to a squarewave.
With a triangle or ramp waveform as one input, the second remaining input and/or the integrated voltage source can be used for controlling the pulsewidth of the squarewave output signal.