The Ondes Martenot; Better than a Theremin

Monotrondes+logo

[Ville] loves the sound of an ondes martenot and decided to build his own. No, it’s not made of vacuum tubes like a 1920s original, this one is made out of a cheap, off-the-shelf analog synth and just a few extra parts.

The ondes martenot is a theremin-like musical instrument; instead of waving your hands around aerials on the theremin, the ondes uses a small ring attached to the player’s finger on a wire loop and a volume lever. The ondes isn’t a common instrument by any means, but Radiohead uses one several in any event.

[Ville] began his build by taking a small, cheap, and new Korg Monotron analog ribbon synth, cracking it open, and reading the schematics. A 100k multiturn pot was wired into the monotron and fastened to a printed paper keyboard with a system of pulleys and a small metal ring. With the multiturn pot wired into the pitch input on the monotron, [Ville] had a semi-accurate and very functional ondes martenot replica.

You can hear [Ville]‘s ondes in action after the break. It’s a little rough starting out, but by the time he’s looping multiple phrases it really does sound wonderful.

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MIDI out for a Korg CX-3 organ

midi-out-for-a-vintage-korg-cx-3-organ

[Michael] loves this old organ of his, but recently he wondered if it would be possible to add MIDI out without altering its original functionality. With a bit of research and more than a bit of hard work he accomplished his goal.

The nice thing about working on a quality piece of hardware like this is the resources you can find regarding how they work (which we bet is tailored for how to repair them when they break). [Michael] found a website with plenty of info on the circuit boards and how they work. From this he was able to locate a few chips which stream serial data regarding which keys have been pressed. Bingo!

Once he located the three signals he was after he built a board to translate them to the MIDI protocol. His circuit is based around an ATtiny2313. It is supported by a liner voltage regulator circuit as well as a buffer chip which converts the incoming signals to the 5V levels needed. His home etched board is clean and well mounted, and the success of the project can be heard in the clip after the jump.

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Programming an Arduino using an audio file

This proof-of-concept is just waiting for you to put it to good use. [Mike Tsao] wrote an Arduino sketch that lets him decode incoming audio data which could be used to program the device. He’s calling the project TribeDuino because it decodes an audio file which is actually the firmware update for a Korg Monotribe.

Earlier in the month [Mike] read our feature on a project that reverse engineered the audio-based firmware update for the Korg hardware. He wanted to see if he could write some code to read that file on his own hardware. All it took was an audio jack and two jumper wires to get the Arduino ready to receive the audio file. His firmware reads the Binary Frequency-Shift Keying encoded data as the audio is played, then echos a checksum to prove that it works.

This would be a fantastic addition to your own projects. Since the audio connection only needs to be mono, it only takes just one Arduino pin to add this jack (the other is a ground connection). Having just played around with alternative ways to push data to a microcontroller ourselves, we might give this a try when we have some free time.

Reverse engineering a Korg Monotribe

Yesterday, Korg released a firmware update to their ribbon controller synth, the Monotribe. The firmware is just an audio file that needs to be played to the sync input of the box. [gravitronic] thought this was rather interesting, so he decided to decode the monotribe firmware. It’s the first step to custom Monotribe firmware, and on the path towards reverse engineering this neat box.

After converting the firmware update to a .wav, [gravitronic] looked at the file with a hex editor and found that each sample is two bytes, and the left and right channels are the same. That made enough sense, so after getting rid of one channel, he sent it through Python to take a look at the patterns of ones and zeros.

Of course, [gravitronic] arbitrarily chose high = 1, low = 0, and little-endianness. The first result didn’t produce a nice “KORG SYSTEM FILE” in the header, so he tried other combinations until the output file looked reasonable. The result is the actual .bin file that’s going to serve as the basis for a nice homebrew firmware. You can grab [gravitronic]‘s Python script here and decode your own firmware.

Adding a Compact Flash reader to a Korg Triton

[Roberto Barrios] has a Korg Triton sampling keyboard which he enjoys very much, but has grown tired of using media of yesteryear to store his work. He had the option of floppy disk or Jazz drive and for a time he was using a floppy-to-USB emulator, but the keyboard still insisted on a 1.44 Mb storage limit using that method. He decided to crack open the case and add his own CF reader.

It should be noted that this hack could have been avoided by using the 25-pin connector on the back of the keyboard. He didn’t want to have external hardware, which is understandable if you’re gigging–it’s just more equipment to keep track of. His solution uses the floppy disk drive opening to mount the card reader. His electrical connections are made with a ribbon cable. He cut off one end, and soldered the individual wires to the contacts on the motherboard. The reader is seen as a SCSI drive by the Korg firmware thanks to a SCSI-to-IDE adapter, so the storage limitation is based quite fittingly on the size of the CF card used.

Look at that cable management. You’d think it came straight from the factory like this!

Archaeopteryx: a large, colorful MIDI controller

This is [Robert Jarvis'] new MIDI controller which he has christened the Archaeopteryx. It makes its home (quite nicely might we add) in a discarded wooden cutlery case. This provides a strong and stable base for the controls while keeping the electrical connections close at hand for any rewiring or repair work.

The interface is made up of several different input devices. The guts from two Korg Nanokontrols donated the sliders and pots. These are both USB devices and they join with a USB keyboard which has been rewired to work with the colorful push buttons. All three devices connect to a hub inside which makes the device work using just one cable connection to the computer.

There’s a lot of wiring shoved into that shallow case. But if he keeps the keyboard mapping straight we think it won’t be too hard to configure the device. We like it that [Robert] included a snapshot of the back-of-the-envelope prototyping plans he made. This kind of ‘how I got there’ information is what we’re looking for when choosing projects to feature.

Monotron Openly Monophonic

Famous synth manufacturer Korg has released the schematics (get them here if you don’t like to fill out forms) for their wee little Monotron for all to see and use! This is great news for anyone looking to build up a synth from scratch or to circuit bend their existing monotron. The filter circuits alone would be fun to add to an existing electronics setup.

Granted there are already many examples of monotron mods out there, but that shouldn’t stop you from experimenting with your own variations. Now with the schematics you can make fundamental changes to the architecture of the synth all from the comfort of your own CAD software. Want more oscillators? Distortion? It’s all out there for you to explore. We’re very interested to see how far people will run with this. And big ups to Korg for recognizing the value of hacking!

[via Retrothing]

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