Resurrecting The Optigan Disc Format


The Optigan and Orchestron were a pair of electronic organs built by Mattel in the 1970s which used swappable optical discs to store instrument information. The discs can still be found today, but the organs are extremely scarce, much to [Gan’s] dismay. After researching the organs for a bit, he decided he could probably build his own MIDI-compatible interface for the audio discs.

The discs have audio waveform data printed on them, which can be read using an LED on one side of the disc and an optical transistor on another. After successfully prototyping a reader that could interpret one of the disc’s audio tracks, he constructed a device to read all of the tracks simultaneously, just like the original organs.

His makeshift turntable was constructed on top of an old record player using acrylic discs and toy car wheels to keep things steady. Once the disc is placed on the turntable, he sets his reader in place, and via some custom circuitry, he is able to play the discs using his much more modern keyboard. It sounds pretty decent as you can see in the video below, though he does admit he would like to tweak a few things to make it sound even better.

[thanks Bryan]


23 thoughts on “Resurrecting The Optigan Disc Format

  1. WOW, well done. This is an interesting concept I’d never heard of. So there are circular tracks on this disk that are recordings of each note you can play and they are all being read at once and the keyboard gates the output of each track.

    Very cool hack, nicely done. And a very cool original concept makes the hack even more worthwhile.

  2. Very cool retro organ/mini/wavetable hack! So how does (or does) the setup compensate for zero crossing pops? Also.. what format is the data in? 8bit audio? Pure analog? (going to have to go google this format some more).. :)


  3. Ah, I was in the national science museum not so long ago and they had this talking clock. That looked very much like this:

    they used optical discs to store the announcers voice. The light reader would physically move to change tracks. So it would say five instead of four for example.

    I wanted to know what those discs were called, there was no information next to machine nor was there anything interesting that I could find on the internet.

    But I am very impressed, nice detail :)

  4. Can anyone link me to some information about scratching the live music as seen from 1:08 to 1:36 in the video with a midi dj wheel? I would love to use that effect!

  5. Awesome. Man look at that pickup, I wish I had skills like that. Sound on the first disc was pretty much amazing cept for the popping, wonder if he can clean that up.

  6. Tweeks, the optical disk has an analog waveform on it, the led and detector circuit make it into a voltage and there is a switch and mixer that lets him play any of the 58 channels (notes) on the disc. The only point it is digital is the midi telling the micro processor switch on a CMOS switch to hear that track.

    So the audio chain is all analog being switch digitally.

  7. @robert

    There really isn’t any pertinent information to send you to. The scratching effect was him physically changing the playback speed of the optical disk. This is just like if you were to scratch a vinyl record of put your finger on a cassette tape. If you want the effect the easiest way is to have a physical medium that you can manipulate. Or, you can do it in software. Doing it in software wouldn’t be that hard…

  8. People who reinvent media readers are my heroes; people who reinvent readers for ridiculously obscure long-obsolete media doubly so.

    Technology-wise, the Optigan looks a lot like a modernized version of the Mellotron…

  9. Instead of controlling the mixing on the receiver side, I’d rather modulate the LEDs individually and go for passive summation. The circuitry required should be a lot simpler.

  10. The poping is caused by an very fast change in the signal level as a note is struck/released.

    He will need a bunch of voltage controled amplifiers to get rid of the popping. that way he can create a slight fade in and a fade out at the start and end of notes respectively. The VCA doesnt have to be anything fancy though, an LED/PhotoResistor(voltage divider) couple would do. Then just add a small capacitance to the led’s on/off signal.

    he could perhaps extend it to have a full ADSR control using these vca’s, and that would make is even cooler still.

    1. indeed, or add a zero-crossing detector to the “player”, so it only starts/stops the note at 0 (which won’t introduce noticable lag since that tend to happen extremely often with them waveforms :)

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