A STM32 Tonewheel Organ Without A Single Tonewheel

The one thing you might be surprised not to find in [Laurent]’s beautiful tonewheel organ build is any tonewheels at all.

Tonewheels were an early way to produce electronic organ sounds: by spinning a toothed wheel at different frequencies and transcending the signal one way or another it was possible to synthesize quite an array of sounds. We like to imagine that they’re all still there in [Laruent]’s organ, albeit very tiny, but the truth is that they’re being synthesized entirely on an STM32 micro controller.

The build itself is beautiful and extremely professional looking. We were unaware that it was possible to buy keybeds for a custom synthesizer, but a model from FATAR sits at the center of the show. There’s a MIDI encoder board and a Nucleo development board inside, tied together with a custom PCB. The UI is an momentary encoder wheel and a display from Mikroelektronika.

You can see and hear this beautiful instrument in the video after the break.

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World’s Smallest MIDI Synth, Now Even Better

We’re pretty sure there’s no internationally recognized arbiter of records like “World’s smallest full-featured polyphonic stereo MIDI synthesizer that fits in a DIN shell”. If there isn’t, there sure should be, and we’re pretty sure [mitxela]’s Flash-Synth would hold that particular record.

This is one of those lessons that some people just can’t leave a challenge alone. First [mitxela] built a MIDI synthesizer into a DIN connector, then a couple of months later he made a somewhat more streamlined version. While both were feats of engineering derring-do, neither was entirely satisfactory. With only square wave synthesis and a limit of eight voices, plus some unpleasant audio issues and a total lack of manufacturability, the next challenge was clear.

We won’t pretend to follow all the audio arcana, of which the video below and the build log have plenty, but the technical achievement is obvious enough. The Flash-Synth has an STM32, a tantalum SMD filter capacitor that dwarfs it, and a few support components on a flexible PCB that folds back on itself twice. This bit of circuit origami is connected to a 5-pin DIN plug and stuffed into the connector’s shell, which in turn mates to a custom-machined metal housing. A stereo audio jack lives at the other end of the assembly, and the whole synth is powered parasitically off the MIDI port.

The first half of the video below is mostly a demo that proves the synth sounds great and can do just about anything; skip to the 22-minute mark for the gory build details. Suffice it to say that [mitxela]’s past experience with ludicrous scale soldering served him well here.

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How Many Commodores Does It Take To Crack A Nut?

It’s brilliant enough when composers make use of the “2SID” technique to double the channels in a Commodore 64 with two sound chips, but even then some people like to kick things up a notch. Say, five times more. [David Youd], [David Knapp] and [Joeri van Haren] worked together to bring us just that, ten Commodore computers synchronously playing a beautiful rendition of the Dance of the Sugar Plum Fairy at this year’s Commodore Retro eXpo.

The feat is composed of nine Commodore 64 computers and one Commodore 128, all fitted with the SID chip. It is a notorious synthesizer chip for utilizing both analog and digital circuitry, making each and every one of its revisions unique to a trained ear, not to mention impossible to faithfully reproduce in emulation. The SID was designed by Bob Yannes at MOS Technology, who later went on to co-found Ensoniq with his experience in making digital synthesizers.

How this orchestra of retro computers came to be, including details on how everything is pieced together can be found on this slideshow prepared by the authors of the exhibition. It’s interesting to note that because of timing differences in each computer’s crystal clock and how only the start of the song is synchronized between them, they can’t play long music tracks accurately yet, but a 90-second piece works just fine for this demonstration.

These synthesizer chips are slowly going extinct since they’re no longer being manufactured, so if you need a new replacement solution, FPGAs can fill that SID-shaped hole in your heart. If you need the whole computer though, the newer Teensy 3.6 will do just fine emulating it all. Check out this beast of a display in action after the break. While we’re at it, this isn’t the only time multiple 8-bit computers have been combined as an orchestra, though these Commodores sound a lot better than a table full of ZX Spectrums.

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XFM: A 32-Voice Polyphonic FM Synthesizer On An FPGA

There’s something about Frequency Modulation (FM) synthesizer chips that appeals to a large audience. That’s one of the reasons behind [René Ceballos]’s XFM project, aiming to duplicate on an FPGA the sound of pure-FM synthesizer chips of the past such as the Yamaha DX series, OPL chip series and TX81Z/802/816. The result is a polyphonic, 32-voice, 6-operator FM synthesizer stereo module.

The project page goes into a lot of detail about the design choices which ultimately led to XFM being implemented on an FPGA, instead of using a dedicated DSP or MCU. Coming from the world of virtual synthesizers running on PCs, [René ]’s first impulse was to implement something on a Raspberry Pi or equivalent. Unfortunately these boards require a lot of power (ruling out battery-powered operation) and can hardly be called real-time, which led [René ] to abandon this attempt.

The design choice against the use of an MCU is simple: though capable of real-time processing, they lack the necessary power to make them a good choice for audio-processing. Working through the calculations to determine what kind of processing power would be needed, it was found that around 650 MIPS would be needed, a figure which most MCUs struggle to achieve a fraction of.

As one of the further requirements for XFM was that it should be as cheap as possible, this ruled out as too expensive the DSP chips which do have the power and hardware features needed. The component chosen was a Xilinx Spartan 6 FPGA, which though somewhat infamous and shunned in FPGA circles turns out to be a very economical option for this project.

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Hacking The Pocket Operator

The number of easily usable and programmable microcontrollers is small, so when selecting one for a project there are only a handful of very popular, well documented chips that most of us reach for. The same can be said for most small companies selling electronics as well, so if you reach for a consumer device that is powered by a microcontroller it’s likely to have one of these few in it. As a result, a lot of these off-the-shelf devices are easy to hack, reprogram, or otherwise improve, such as the Robot Pocket Operator.

The Pocket Operator is a handheld, fully-featured synthesizer complete with internal speaker. It runs on a Cortex M3, a very popular ARM processor which has been widely used for many different applications, and features everything you would need for a synthesizer in one tiny package, including a built-in speaker. It also supports a robust 24-bit DAC/ADC and all the knobs and buttons you would need. And now, thanks to [Frank Buss] there is a detailed teardown on exactly how this device operates.

Some of the highlights from the teardown include detailed drawings of how the display operates, all of the commands for controlling the device, and even an interesting note about how the system clock operates even when the device has been powered off for a substantial amount of time. For a pocket synthesizer this has a lot to offer, even if you plan on using it as something else entirely thanks to the versatility of the Cortex M3.

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A Baby Named DJ

Some of us are guilty of picking up questionable hardware from garage sales, fleamarkets, and well-meaning relatives. There is a balance between turning down a good investment and hoarding, and if we figure out how to tell the difference you will be the first to know. [Clem Mayer] may start on the side of unwise acquisition, but he pushes a broken fetal detector into the realm of awesome by converting it to an analog synthesizer, born to headline at an Eastern European dance party.

He starts with a basic teardown, and we get to see how old hardware was serviceable with only two standard screws. It is a good thing too, because the nickel-cadmium batteries are older than some of you and they are in need of replacement. New nickel-metal hydride batteries got it up and running but [Clem] does not have a baby bump so its functionality turned to Pink Floyd era synthesizer circuit bending. Circuit bending involves modifying a circuit for sound it was not intended to make.

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Hack My Wired Heart

Liner notes? Passé. In Berlin, the release of a special edition synth-wave record came with an accompanying experimental synthesizer called Wired Heart.

At the core of this adorable heart-shaped synth, designed by music technology enthusiast [tobi tubbutec], is the classic 74HCT14 chip with six Schmitt trigger oscillators. The bright red PCB has eight gold touch and humidity sensing pads that activate and modulate these oscillators. As well as changing the sounds by playing with pressure and conductive liquids you can use the six sets of header pins on board to plug in your own components for noisy experimentation. Wired Heart ships with LEDs, photoresistors and a potentiometer, but we’ve also plugged our own DIY fabric pressure sensors into this synth to make some excellent electronic sounds.

In the Hackaday.io post linked above, [tobi tubbutec] walks us through a number of the circuit design decisions he made while prototyping his “cardiotronic human-touch hexoscillatric stereo esoteric snythespacer”. We enjoyed his creative and sometimes unconventional designs, from his inclusion of non-functioning traces for aesthetic reasons to his chosen method of hard syncing — injecting a small pulse of one oscillator into the other. If you want to examine his layout in more detail, [tobi tubbutec] has helpfully included the KiCad schematic file in his write up.

This adorable, hackable synth caught our eye at this year’s SuperBooth — an annual indie electronic music conference in Berlin that’s well worth checking out if odd noises and handmade electronics are your thing —  but it’s recently been listed on Tindie too. To listen to the upbeat synth-wave record Wired Heart originally shipped with, visit the artist Hyboid’s bandcamp.

If you’re interested in experimental musical instruments and synthy chip tune you’ll also love [jarek319]’s Sega Genesis synthesiser.

Check out a demo of the Wired Heart synth in the video after the break.

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