MagicQuartz: Speed Control for Turntables

MagicQuartz is a microcontroller firmware for the accurate speed control of HiFi record players with AC motor. The highly configurable software can be used for control and signal generation in true sine wave inverters, enabling the implementation of precision turntable speedboxes or motor power supplies.

The following illustration shows a typical application of MagicQuartz:

Typical application of MagicQuartz

MagicQuartz aims to perfect the playback speed of vinyl records. It not only offers complete decoupling of a turntable from mains frequency fluctuations, but also electronic switching and adjustment of the turntable’s speed. It is even possible to have the speed continuously monitored and automatically readjusted. MagicQuartz is also a valuable tool for the reproduction of historical shellac records, as non-standard speeds can be easily set.

MagicQuartz has been developed for the 8-bit AVR microcontroller family from Microchip (formerly Atmel). In the context of rapid prototyping, the firmware can also be run directly on Arduino hardware, such as the Arduino Mega 2560 Rev3 (see image above, left). To interact with the firmware, an LCD keypad shield or a serial connection via the Arduino’s USB interface can be used.

MagicQuartz is aimed at professional hardware developers from the absolute high-end audio sector, as well as private audio enthusiasts with appropriate knowledge in electronics. An easy to reproduce technology demonstration, the so-called MagicQuartz TechDemo, consisting of a fully 3D printable enclosure and an electronic circuit, is available under an open source hardware license (see image above, right).

For a complete list of all features please refer to the extensive documentation.

MagicQuartz is a proprietary software that needs to be activated for full functionality. Without activation, the software operates in a usable but limited demo mode that is intended for evaluation and hardware development purposes (see documentation). It’s free: Full licenses for personal use are currently free of charge. If you would like to activate a license, please send me an e-mail: Contact Information

MagicQuartz Resources

MagicQuartz TechDemo turntable speedbox, bottom view

Another rendering of the MagicQuartz TechDemo, created with OpenSCAD.


What initially started as a crazy idea soon developed into the ambitious goal of developing the world’s best speed control for turntables. The project now looks back on over a decade of passionate research and development (admittedly with major breaks in between):

  • January 2011: First crude square wave inverter capable of driving a Dual 1219 at 220V/50Hz (image below, top left). Implemented using an Atmel STK 500 and ATmega32. Back then, the firmware was called “MultiQuartz”.
  • January 2015: Demonstration of a first turntable speedbox based on the more modern ATmega328P (image below, top right). A specially developed digital sine wave inverter based on an H-bridge was used. MagicQuartz firmware version 0.9.
  • 2021-2022: Continued development and porting of the firmware to the ATmega2560 and development of the “MagicQuartz TechDemo” (image below, bottom).
  • April 2023: Release of MagicQuartz 1.0, “Phoenix”.
MagicQuartz TechDemo turntable speedbox, photograph