schlappi-engineering-angle-grinder

Schlappi Engineering Angle Grinder

Quadrature sine oscillator, state-variable filter and feedback waveshaper

18 HP Eurorack module

Angle Grinder is an all-analog, OTA-based module with two interacting sections. SPIN is a quadrature sine-wave oscillator producing four phase-related outputs (0, 90, 180, 270 degrees). GRIND is a network of four comparators, four VCAs and a mixer that compares each SPIN phase against an input signal and subtracts the result, generating complex waveshapes. When GRIND is fed back into SPIN (via the GRIND -> SPIN knob) the four outputs transform into a state-variable filter (low-pass, band-pass, high-pass, inverted band-pass) and the GRIND sliders become voltage-controlled nonlinear feedback paths for harsh, unpredictable timbres. Whether it behaves as an oscillator, filter or distortion effect depends on the knob positions and the presence of an input signal.

Features

  • All-analog OTA-based quadrature sine oscillator
  • Four phase-related outputs: 0, 90, 180, 270 degrees
  • Doubles as a state-variable filter (LP/BP/HP/Inv-BP)
  • GRIND section: four comparators, four VCAs and a mixer
  • Voltage-controlled harmonic waveshaping with no input
  • Compares and subtracts each phase against an input signal
  • GRIND -> SPIN feedback turns the oscillator into a filter
  • Four GRIND sliders, each separately voltage-controllable
  • LOW range 0.1Hz-500Hz, HIGH range 10Hz-20kHz+
  • Tracks 4+ octaves of V/Oct
  • FM 1 linear or exponential (rear header), normalled to GRIND OUT
  • FM 2 additional exponential V/Oct input

Controls & Jacks (25)

  • Grind 1
  • Grind 2
  • Grind 3
  • Grind 4
  • Spin
  • Range
  • IN
  • Grind → Spin
  • Fine
  • Damping
  • FM 1
  • In
  • Out
  • Inject In
  • V/Oct In
  • FM 1 In
  • FM 2 In
  • Grind CV 1 In
  • Grind CV 2 In
  • Grind CV 3 In
  • Grind CV 4 In
  • Phase 0 Out
  • Phase 90 Out
  • Phase 180 Out
  • Phase 270 Out

How-To Guides

  • Quadrature sine source
  • Self-oscillating GRIND timbres
  • State-variable filter
  • Supersaw / metallic waveshaper
  • Soft sync via Inject

Explore the interactive Angle Grinder panel on BleepDex — tap any control to learn what it does.

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