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Thread: Block diagram or description of analog abstract generators?

  1. #1
    Join Date
    Dec 2007
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    Stockholm, Sweden
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    Default Block diagram or description of analog abstract generators?

    Hi,

    I'm interested in learning more about analog abstract generators but I find it hard to get any good info!
    I have acess to a lot of really complex modular synths and would like to use them to generate something beyond lissajous patterns, oscilloscope-like audio modulated saw-sweeps and such.
    I have tried to inserts VCA:s and ringmods in the signal chain to make some aspects controllable but most of it looks sort of the same! Ways to make more geometric shapes, squares and maybe pointy objects would be cool and also know more about the building blocks for making the image rotate and other semi-3D operations.

    I have an old geometric correction card attached to a pair of really old scanner drivers, I have been thinking of putting proper potentiometers on it and make it a module in my abstract modular, what do you think about that?

    Any veteran laserists want to educate a poor victim of the digital generation?

  2. #2
    Join Date
    Jun 2009
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    St. Louis, MO
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    OK

    In the beginning there were open loop scanners and they were pretty cool. They couldn’t handle square waves, or even triangle waves, but Duh… If you sent them a sudden waveform jump they would do their best, and the ringing could be really interesting especially in dynamic waveforms. But the imagery of old was mostly done with several quadrature oscillators. A quadrature oscillator has two outputs. The second output is phase shifted 90 degrees to the first output. With two quadrature (sine/cosine) oscillators with the right frequencies and gains you get a square or a triangle or a star or a pentagon… you get the idea. A third oscillator lets you get more complex. Then throw in spirals, amplitude & frequency modulation, z axis rotation, etc. and you’re really beginning to have some fun. Oh, add polarity switch to invert one output of the quadrature oscilators...

    Brian

    P.S. The block diagram below is part of the Laserium patent from the 70's
    Click image for larger version. 

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  3. #3
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    Thanks, exactly the type of tips I was looking for!
    I have a few sin/cos oscillators and ringmods/four quadrant modulators, I'll try to patch something up! When mixing the two oscillators, do I mix the two 0 degree signals and send to X and the 90 degree signals to Y?

    I feel like I'm just peeking into another money/time pit here...

  4. #4
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    The 4QMMs are useful for building up z axis rotators. We used 2QMMs for spirals and other gains. ( i never really looked at Laserium's 2QMM circuit closely, but I assume the reason we built our own was to insure they went all the way to zero.) I can't visualize where ring modulators whould be particularly useful...

    Below is a diagram of a basic quadrature oscillator control scheme.

    Click image for larger version. 

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    Quote Originally Posted by dar303 View Post
    Thanks, exactly the type of tips I was looking for!
    I have a few sin/cos oscillators and ringmods/four quadrant modulators, I'll try to patch something up! When mixing the two oscillators, do I mix the two 0 degree signals and send to X and the 90 degree signals to Y?

    I feel like I'm just peeking into another money/time pit here...

  5. #5
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    Dec 2007
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    Thanks again! That is about how I ended up patching, two of these circuits into a mixer and then some LFO:s and slope generators to modulate different parameters. I used a Serge TKB keyboard/sequencer as a simple preset storage and a oscilloscope as a preview device.
    I see that I can make a lot of cool stuff with the modulars but I think it would be much more practical to have dedicated hardware with better (DC coupled) VCA:s/2QMM's and DC coupled mixers with invert and offset controls but make a s many of the parameters as possible voltage controlled so the synth can be patched in when needed but keep the main signal path on dedicated hardware.

    I made some progress, managed to get my new scanners up and running and a basic patch with two quadrature oscillators, a few DUSG's and some mixers plus a TKB as patchstorage.

    I made a pentagram!
    (It's a bit hard to focus the camera)


    Here is the synth:


    And here is a lumia projector I built to go with the synth-kit.
    It's a casio diode, 150mm discs from ornamental glass and it has a Flexmod P3 so I can control it and fade/strobe from the synth.

  6. #6
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    A friend took this picture of the projections with his Hasselblad medium format camera, this is a low res preview:




    It was fun doing this "for real" at the Modern Museum in Stockholm, the artist that made the audio was very happy and we will probably do it again in a more developed way, might even pay me to build some custom modules!

  7. #7
    Join Date
    Nov 2013
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    St George UT
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    If there is still any interest in this subject, I have a number of articles and schematics from the late '70's and early 80's. All of these projects were intended to make "abstracts" on an oscilloscope, but it wasn't much of a stretch to do laser art with them. In spite of the age of this stuff, a number of the parts, although obsolete, are still available, and many (multipliers) can be replaced with current production chips.
    I'm hoping that other old analog dogs will share their stuff as well. I, for one, am looking for multiplier schemes that incorporate perspective control.

  8. #8
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    Oct 2012
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    Hello,

    I would be interested in anything you are willing to share.

    ED

  9. #9
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    St George UT
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    The stuff I have is currently in .jpg scans, and in some cases the articles are not complete. There is enough content that has survived that you'll get the idea.
    I'll start converting the scans to .pdf files and start posting in a day or two. I'll also include notes based on my experience with the projects. Honestly, I could never be considered a "laserist" but I had a lot of fun with this stuff. My forte was beam shows- I worked for LaserMedia in the early '80's and toured internationally with several name acts.
    The bug bit me again when I started reading about these cool little RGB diode bundles you can pick up for a few hundred dollars. Back when I was doing it professionally, the price for a white light laser of similar power could exceed $17,000.

  10. #10
    Join Date
    Oct 2012
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    Carver, MA.
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    Hello,

    Awesome! That would be great.

    If it is easier, I will convert your .jpg files for you. Just ask.

    I am currently in the process of designing an analog console of my own.

    ED

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