First revealed last month, PreenFM is an open source hardware synth. As the name implies, it’s an FM synth, with some very serious specs: up to six-operator FM synthesis with some nine algorithms, up to 4-voice polyphony (depending on algorithm), glide, selectable LFOs, modulation matrix, and preset banks with SysEx support. It’s all usable via a display and MIDI support.

It’s also fully open source hardware; whereas early efforts often had commercial restrictions attached, PreenFM is free for use under the GPLv3 and Creative Commons. And it’s got a unique platform under the hood: the open source LeafLabs 32-bit development platform gives this some serious horsepower. It’s very much in contrast to the ultra-inexpensive 8-bit brain of our own MeeBlip synth; think of the MeeBlip as an exercise in what you can do with a little two-stroke engine versus the V8 muscle in this. (The creator says the MeeBlip helped inspire his creation – yes, synths are multiplying!)

You may have glimpsed the PreenFM making the rounds online, but I got creator Xavier Hosxe to tell us more of the gory details and share some sounds.

CDM: So this is all based on the Leaf platform?

Xavier: Yes it’s built around a LeafLab board.
I coded a first version on the Maple [development board]; then when they announced their “Maple Mini,” I realized it was going to be very easy to plug it into a PCB.
I’m not directly connected to [LeafLabs]; I participated in the forum and learnt many things from the team.

They are very friendly and helpful.

What was it like working with the Leaf?

The LeafLabs boards uses an ARM Cortex-M3 microcontroller.

It’s a 32-bit chip runing at 72Mhz that can do 32-bit multiplication in 1 clock cycle, has 128Kb of flash [memory] and 20Kb of RAM. That seems very few but it’s not, PreenFM software uses 92Kb for the moment.

LeafLabs provide a Linux/gcc toolchain that allows to develop in your IDE of choice… Eclipse in my case, which is very confortable.

They also provide a strong bootloader and some libraries that worked perferfeclty for my needs : Usart (Midi), I2C (EEPROM), LiquidCrystal (LCD).

What will you get in the PreenFM kit?

All you need to build yourself a complete synth: PCB, screws, resistors, ICs, audio/midi jack, box, 20×4 LCD, encoders, knobs, buttons… even an USB cable [for power].

You’ll also get a Maple Mini board with PreenFM soft preloaded. The Maple Mini is easily updatable, and you can experiment lots of different things with it.

PreenFM C++ source code is available on GitHub. It’s easy to read and modifiable. If you want to see your name to welcome you on the boot screen, go ahead 😉

To build the kit, you only need a soldering iron and some solder.

There will be 2 differences with the photos you can see on the site: the final PCB will be blue (I should receive them next week). [Ed.: See the photo in blue at top; the orange one is included here for variety! -PK]

Xavier also sends along some welcome news:

Here is a sound I can get with my soon-to-be-released StepSequencer feature in PreenFM.

This is a single voice of a simple 3-oscillator voice. 1 very slow LFO + 2 * step sequencer routed to the modulation indices.

PreenFMStepSeq by cdm

Here’s a sound sample:
PreenFM 1 by cdm