Schlappi Engineering - Angle Grinder

The Angle Grinder is an analog OTA based quadrature sine wave oscillator, filter and waveshaper. It is composed from two sections. The Spin section features four phase related outputs, with 1volt per octave tracking and linear and exponential FM inputs. The Grind section provides voltage controlled harmonic content, creating complex waveshapes. The position of the knobs can turn the module into a state variable filter -A flexible tool for tone sculpting!

The Schlappi Engineering Angle Grinder combines two different sections: Spin and Grind.

The Spin section is a quadrature sine wave oscillator with four phase related outputs (0°, 90°, 180°, and 270°). It tracks up to four octaves at the 1 volt per octave input. It can act as an oscillator or LFO thanks to a selectable range:

• High range: 10 Hz to over 20 kHz
• Low range: 0,3 Hz to over 600 Hz

The FM1 can be switched from linear to exponential using a jumper in the back of the module, and the amount of modulation is controlled by the FM1 knob. The FM2 input adds an additional exponential 1volt per octave input without attenuation.

The Grind section consists of four comparators, four VCAs and a mixer. With no input, the Grind section provides voltage controlled harmonic content thanks to the four associated CV inputs at the bottom of the module. If a signal is patched in the audio input, it compares each phase against the input signal. Each slider then subtracts the compared signal from the input signal, creating complex waveshapes.

When Grind is fed into the Spin section using the „Grind > Spin“ potentiometer, the outputs become a state variable filter with low-pass, band-pass, high-pass and inverted band-pass.

The Damping potentiometer is able to neutralise the oscillation, and allows an external signal to pass through. Then the Grind section becomes a nonlinear feedback network for harsh and unpredictable timbres. The four phase feedback paths can be separately manually and voltage controlled. Thanks to the Inject input it is possible to add a second input for either audio or CV, bypassing the Grind section.