schlappi-engineering/angle-grinder
Angle Grinder
Quadrature sine wave oscillator, state variable filter, and voltage-controlled waveshaping/distortion effect. The SPIN section outputs four phase-related sine waves (0°, 90°, 180°, 270°); the GRIND section compares each phase against an input signal and subtracts the result, producing complex waveshapes or nonlinear feedback filter outputs. All analog OTA-based design.737
Capabilities 3
- Quadrature Sine Wave VCOquadrature-vco
- SPIN section outputs four quadrature sine waves (0°, 90°, 180°, 270°) from a single OTA-based oscillator core. HIGH range 10Hz–20kHz+, LOW range 0.3Hz–600Hz+. Tracks 4+ octaves V/Oct.737
- State-Variable Filterstate-variable-filter
- When GRIND is fed into SPIN and DAMPING is increased, the oscillator stops and the four outputs become LP, BP, HP, and inverted BP responses. GRIND sliders become nonlinear feedback paths in filter mode.737
- Waveshaper / Wavefolderwaveshaper
- GRIND section compares each SPIN output phase against input signal and subtracts the result; sliders independently control each phase path. With no input, provides voltage controlled harmonic content.737
Jacks 14 — 9 in / 5 out
| Name | Signal | Voltage | Description |
|---|---|---|---|
| Inputs (9) | |||
| FM 1 | cv | — | FM input with attenuator knob. Selectable linear or exponential FM via jumper on rear. Normalled to GRIND OUT when no cable is inserted — turn down when tracking pitch.737 |
| FM 2 | cv | — | Additional exponential V/Oct FM input for the SPIN oscillator.737 |
| GRIND CV 1 | cv | 0V to 5V | 737 |
| GRIND CV 2 | cv | 0V to 5V | 737 |
| GRIND CV 3 | cv | 0V to 5V | 737 |
| GRIND CV 4 | cv | 0V to 5V | 737 |
| IN | mixed | — | Main input to the GRIND section. Accepts audio or CV. The 90° SPIN output is normalled through an all-pass filter to this input when nothing is plugged in.737 |
| INJECT | mixed | — | Direct input to the SPIN oscillator/filter core, bypassing the GRIND section. Header-selectable AC or DC coupling (AC by default). AC mode creates spikes from square/saw waves for soft sync. DC mode adds the input signal directly to the core.737 |
| V/OCT | cv | — | Volts-per-octave pitch CV input. Tracks 4+ octaves.737 |
| Outputs (5) | |||
| 0° Out | mixed | -2.5V to 2.5V | 0° phase SPIN output. Sine wave at ±2.5V when oscillating; LOW PASS filter output when filtering.737 |
| 180° Out | mixed | -2.5V to 2.5V | 180° phase SPIN output. Sine wave at ±2.5V when oscillating; HIGH PASS filter output when filtering.737 |
| 270° Out | mixed | -2.5V to 2.5V | 270° phase SPIN output. Sine wave at ±2.5V when oscillating; INVERTED BAND PASS filter output when filtering.737 |
| 90° Out | mixed | -2.5V to 2.5V | 90° phase SPIN output. Sine wave at ±2.5V when oscillating; BAND PASS filter output when filtering. Normalled through an all-pass filter to the GRIND IN when no cable is plugged into IN.737 |
| OUT | mixed | — | Main output from the GRIND section. Not amplitude-limited; can reach up to 22Vpp (±11V).737 |
Parameters 12
| Name | Type | Range | Behavior |
|---|---|---|---|
| DAMPING | knob | — | Counteracts the oscillations of the SPIN section, allowing an external signal through. Increasing DAMPING is required for filter operation.737 |
| FINE | knob | — | Fine tuning control for the SPIN oscillator frequency.737 |
| FM 1 Knob | knob | — | Attenuator for the FM 1 CV input. Mode (linear or exponential) selectable via rear header jumper.737 |
| FM1 Mode Header | jumper | — | Selects whether the FM 1 jack operates in linear or exponential FM mode.737 |
| GRIND -> SPIN | knob | — | Feeds the GRIND output back into the SPIN oscillator core. As turned clockwise, transforms phase outputs into nonlinear feedback paths. When turned up with an external input and DAMPING increased, switches the module from oscillator to state variable filter operation.737 |
| GRIND IN | knob | — | Mixes the amount of signal fed from the SPIN outputs into the GRIND section. Must be turned up to get signal out of GRIND when no external input is present.737 |
| GRIND Slider 1 | fader | — | 737 |
| GRIND Slider 2 | fader | — | 737 |
| GRIND Slider 3 | fader | — | 737 |
| GRIND Slider 4 | fader | — | 737 |
| INJECT Coupling Header | jumper | — | Selects AC or DC coupling for the INJECT input. AC (default) creates a high-pass response that turns square/saw waves into spikes for soft sync. DC mode adds the full input signal directly to the oscillator core.737 |
| RANGE SWITCH | switch | 0.1Hz – 20000Hz | Selects between LOW (sub-audio to LFO range) and HIGH (audio range) frequency spans for the SPIN oscillator.737 |
Firmware history 0 versions
No firmware history recorded.
References 2
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[737]
Schlappi Engineering Angle Grinder Manualmanual● verified 2026-05-22
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[738]
Schlappi Engineering Angle Grinder product pageproduct_page● verified 2026-05-22