Reviving a Vintage Audio Control Panel as a Modern Sequencer

An unfortunate consequence of the rapid development of technology is the rapid pace at which electronic devices become obsolete. We often see very well-made hardware end up covered in dust within just a few years, because the underlying technology is no longer relevant. To save that high-quality hardware from the e-waste mountains of the world, many makers get creative and turn to upcycling. That’s how bitluni was able to revive a vintage audio control panel as a modern ESP32-based music sequencer/synthesizer.

While attending the Hackaday Supercon in California this year, bitluni visited the Apex Electronics Surplus store in LA. That store has a massive variety of old electronic devices and components, where bitluni found a control panel from a ‘90s audio workstation. That would have been a very high-end workstation for professional audio engineers that contained several of these control panels. Each panel has 16 rotary encoders in a 4×4 grid. Every encoder has its own four-digit VFD-style display and mode button with LED indicator, and the encoder knobs also have an outer ring of LEDs to show volume, amplitude, intensity, or anything else. Finally, every column has a keypad at the bottom with 12 buttons, each with an LED indicator.

That’s a lot of nice hardware in a compact interface, making it quite desirable. Bitluni and a friend at Hackaday both started reverse-engineering the device, with that friend (Jeoen Domburg, AKA “Spritetm”) unlocking everything by gaining access to the FPGA (Field-Programmable Gate Array) controller. With that access, bitluni was able to use the controls however he liked.

To achieve that, bitluni designed a custom PCB that plugs into the control panel’s bus interface. That PCB contains an ESP32 microcontroller that reads button presses and encoder positions, and also sets the displays and LEDs. He chose to use the ESP32 to create a synthesizer/sampler sequencer that uses the knobs and buttons to play either synthesized tones or sampled WAV files in repeating patterns. The ESP32 outputs audio as 1-bit, because most of the microcontroller’s pins were needed to interface with the panel. The quality isn’t great, but it has a nice lo-fi sound that is appealing for certain music.

Bitluni originally pushed that audio output through a small amplifier board to a speaker, but that lowered the quality even further. He ended up feeding the audio as a line-out signal, which he can connect to an external speaker system or his camera’s mic input. As you can hear at the end of his video, this works quite well and was surprisingly affordable to build using this otherwise obsolete piece of vintage tech.