DIY Dub Machines: Samplotron

US Homebrew MIDI Sampler running on ESP32 13/05/26

The Samplotron is a project is based around the ESP32; a lightweight homemade hardware sampler that can trigger sounds on command via MIDI. The full build is explained by [Jakub] it's creator on Medium and was brought to our attention by Hackaday. Here are some of the specs... it looks and sounds like a genuinely great little sampler!

Current Features

WAV sample playback from /samples on SD.

32-voice polyphony with deterministic oldest-voice stealing.

Retrigger starts a new voice instance and softly fades older voices from the same sample group.

Playback format for assigned samples is enforced to WAV PCM16, 44.1kHz, mono.

Audio playback runs in a dedicated FreeRTOS task/core with trigger events passed by queue.

SD and RAM playback share the same voice engine and mixer pipeline.

OLED UI with 2 encoders (via MCP23017).

On-device MIDI note to sample assignment.

Per-sample SHOT/LOOP playback mode (stored in config).

Persistent assignments, sample volumes, and playback mode in sampler_config.json.

Automatic RAM preload for short samples (faster trigger response).

There's a load of detail on the project on GitHub, and here's an excerpt from the article written on Medium:

For a while, I had been looking for a simple sampler -- not a full-blown beat-making machine, just something that could play back samples live on stage. The Akai MPX seemed like a good fit, but unfortunately its software can crash in a way that effectively bricks the device. I also own a Korg Volca Sample, which I tried using with pads, but it works much better as a beat machine.

I had also always wanted to build my own system with a small screen, like many hardware instruments have.

So I decided to build a sampler -- not just for that one synth tom sound, but something that would give me quick access to sounds on stage, with the ability to trigger samples from any MIDI controller. I already had a Korg nanoPAD2 and a USB MIDI host, so I used those.

After some research, I settled on the following setup:
- ESP32-A1S -- a microcontroller with solid audio capabilities and the necessary peripherals, especially an SD card slot
- standard 5-pin DIN MIDI input
- a 2.42" 128×64 OLED display with yellow pixels,
- two rotary encoders connected via an MCP23017,
- analog master volume control plus per-sample digital volume,
- a metal enclosure.

I worked on the software and the enclosure in parallel. Somewhere along the way, I discovered Milliput epoxy putty, which turned out to be a fantastic solution for hand-crafting enclosure elements replacing prefabricated plastic parts.

Read the full article on Hackaday and go deep with Jacobs post on Medium.