The SPIN section is a quadrature sine wave oscillator. The GRIND section compares each phase against the input signal, then subtracts the resulting square waves from the input signal. If the spin section is either damped enough or enough signal is fed into it from the GRIND section then it will stop oscillating and become a state variable filter.

The Angle Grinder tracks volts per octave and can be used as a sine wave oscillator with voltage control over harmonic content available at the GRIND OUT. With no input it’s four phase related sine outputs (0°, 90°, 180°, and 270°) remain clean from 0.1Hz to over 20kHz and are suitable for quad panning or XY applications.

With an input signal applied the GRIND out ranges from quadrature pulse width modulation (at LFO rate) to sync-like metallic tones (at audio rate). When GRIND is fed into the SPIN then it becomes a nonlinear feedback network with the faders and corresponding CV inputs providing instinctive control over phase cancellation, oscillation, and distortion. The four phase related outputs will become low pass, band pass, high pass, and inverted band pass filter outputs.

The function of the Angle Grinder depends on both the position of the knobs and the presence of an input signal.


  • Quadrature Sine wave VCO with four phase related outputs: 0°, 90°, 180°, 270°
  • HIGH range from 10Hz to over 20kHz
  • LOW range from 0.1Hz to over 500Hz
  • Tracks volts per octave at the V/OCT input
  • FM1 is selectable linear or exponential FM via jumper on back
  • FM2 is additional exponential V/OCT jack
  • With no input GRIND section provides voltage controlled harmonic content
  • With input GRIND section compares each phase against GRIND IN signal
  • Each slider subtracts the compared signal from the input signal, creating complex waveshapes
  • When GRIND is fed into the SPIN section the outputs become a state variable filter
  • DAMPING counteracts the oscillation and allows an external signal through
  • When filtering the four phase related outputs are: LOW PASS, BAND PASS, HIGH PASS, and INVERTED BAND PASS
  • When filtering the GRIND section is a nonlinear feedback network for harsh and unpredictable timbres
  • The four phase feedback paths can be separately voltage controlled
  • The INJECT jack can be used as a second input for either audio or CV, bypassing GRIND
  • All analog OTA based design
POWER DRAW:+12V 81mA, -12V 78mA
MAP: $310



The Interstellar Radio is a faulty transmission line providing several varieties of destructive effects as well as acting as a non-volts/octave complex oscillator when no input is provided.

Interstellar radio converts an audio signal from the input jack to a high frequency pulse train and then back to an audio signal with voltage control over the clock for the up conversion (CARRIER) as well as the down conversion (DEMODULATOR), like a voltage controlled radio transceiver designed for poor reception.

Manipulating these clocks allows for a variety of aliasing, distortion, and frequency modulation type effects. The output is also sent to a comparator along with the input, and the result is available at the “ERROR” output for a ring modulation type effect.

When no input is provided a DC offset (controllable with the input jack) sets a frequency for the up conversion (which is effectively a VCO), the down conversion acts as a modulation oscillator allowing for a fairly radical form of frequency modulation. Two audio signals can be inserted into the clock input jacks and modulate each other in the same way.


  • Simulates the process of modulating and demodulating a signal for radio transmission
  • Effect or complex oscillator (non v/oct)
  • Voltage controlled aliasing, distortion, and frequency modulation effects
  • Two wide ranging voltage controlled square wave oscillators with individual outputs
  • CARRIER oscillator converts input into high frequency pulse train
  • DEMODULATOR oscillator inside control loop brings sound back to audio range
  • CV applies external voltage control to oscillators or uses input signal as audio rate FM
  • Internal oscillators can be replaced with external modulation sources
  • TYPE selects demodulation loop type (changes timbre and response)
  • ERROR output with threshold control
  • TONE control for filtering out the harshest of frequencies
  • All analog design
POWER DRAW:+12V 40mA, -12V 30mA
MAP: $195

The following retailers for Schlappi Engineering include:

Analogue Haven
London Modular
Midwest Modular
Modular 8
Perfect Circuit Audio
SchneidersLaden GmbH
Signal Sounds
Three Wave Music