QuadMod Controls

Quadmod

Quadmod

Quadmod is a Eurorack modular four channel effect module. A modulation section allows either phasing or flanging followed by a delay. As part of the Mountjoy Modular polyphonic range the module uses a series of intermodulation paths to convert a four channel input to a stereo output.

Phaser

The phaser uses 4 (configurable up to 16) all pass filters to create the phasing effect. Each channel's all pass filter is 45° out of phase with the last. The regeneration (feedback) control progressively mixes one channel to the next to widen the stereo spectrum.

Flanger

The flanger uses multiple short modulated delays to create a flanger/chorus effect. The delay times are modulated with a 45° phase shift from channel to channel. A wide option (on by default) mixes a further 180° phase shifted version of each channel's signal to the next channel.

Technical

Quadmod uses an STM32563 microcontroller which controls a four channel Audio Codec (AsahiKasei AK4619) using SPI for configuration and SAI (Serial Ausio Interface) peripheral to manage the 4 in and 4 out I2S audio streams. The microcontroller reads the front panel controls with internal 12 bit ADCs.

A USB socket is provided for serial configuration and a web editor using WebSerial provides a UI for editing settings. Three LEDs are controlled with PWM from the MCU to indicate modulation LFO rates and delay times.

Construction is a sandwich of three PCBs with a component board, a controls board and a panel. PCBs designed in Kicad v7.

Components schematic

Controls schematic

In addition the the Eurorack +/-12V rails (which have polarity protection and filtering) a digital 3.3v rail is supplied using a TI TPS561201 and analog 3.3v is generated with an LM1117-3.3.

Errata

Version 1 of the component PCB had microcontroller pins PC0 (SAI2_SD_A) and PC1 (DLY_TIME_POT) flipped.