Function Generator for synth

Discussion in 'The Projects Forum' started by Treeman, Jun 11, 2014.

  1. Treeman

    Thread Starter Member

    May 22, 2014
    158
    15
    Hi, a keyboardist friend has set me a task to build him a synth!

    Can I build a function generator and use that as a basis for a synth?

    I have a schematic for a sine/sq/tri using an 8038 IC. What other chips should I look at please?
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    While today's synthesizers are mostly digital boxes calculating stuff and playing sampled waveforms, the term synthesizer comes from the way these things started out. They synthesized the sound of a musical instrument or voice with basic waveforms, noise sources, and envelope shapers, not a microprocessor in sight. If you want to go that route, search the innergoogle for old documents and plans from PAIA. They were small kits that could be combined to basically emulate a Moog, the gold standard of the day.

    God I miss Popular Electronics.

    ak
     
  3. Treeman

    Thread Starter Member

    May 22, 2014
    158
    15
    Thanks AK. Will do, he wants modular old skool which is lucky for me!
     
  4. Veracohr

    Well-Known Member

    Jan 3, 2011
    549
    75
    Treeman likes this.
  5. Treeman

    Thread Starter Member

    May 22, 2014
    158
    15
    What a great site Vera with stripboard layouts too!
     
  6. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Treeman
    There is something important you have to understand about analog synthesizers. The music VCOs are not linear, they are logarithmic.
    An example
    A 8038 IC VCO voltage verses frequency
    1V = 100Hz
    2v = 200Hz
    3V = 300Hz
    4V = 400Hz
    etc.
    a music VCO works this way
    1V = 100Hz
    2V = 200Hz
    3V = 400Hz
    4V = 800Hz

    Look at the schematic of the "VCO 1V/octave" in the Music from outer space link. There is a matched transistor set that is thermally coupled to a Palladium film compensation resistor. This is the heart of a precision log amp. You must get those parts or you have no hope of making it work. It will not be an easy task to tune this thing unless you have a precision volt meter and a musical tuner.

    It is not a simple task you have signed up for.

    Mark
     
  7. Treeman

    Thread Starter Member

    May 22, 2014
    158
    15
    Having spent ages looking at the schematics on music from OS I heartily agree lestraveled. I obviously have a big mouth but am still unable to masticate properly!
    Thanks very much for your input - I was wondering if I should start off with a kit - I need building experience and a week off the kids to start the AAC worksheets for any of it to make sense. I have no hope of planning the layout of something so complex but feel its cheating to buy a pcb - i'll have to drop that attitude to continue methinks.
    Nevertheless there is much on the website that helps/inspires and I have already built a useful companion from the website which i'll blog in a few days.
    At least I understand the log/linear issue from an ear perspective even if my mnemonics for pot markings were wrong. Decided yesterday to start GCSE Electronics in September at night school. Poor teachers.....
    Thanks again I don't want to build something that works well but is useless. Like some of my 'projects' this one may take a few years to become reality but I need some lofty goals. Its interesting how electronics is changing my gung ho character-planning and organisation are everything.
     
  8. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    It is not cheating to buy a PCB when you are inexperienced at laying one out and building it.

    I suggest the following: Download the PCBExpress software (free). Using the picture of the VCO PCB and the schematic, lay out a copy of it (both schematic and PCB.) Doing this with teach you the software. (Its a very simple program.) Now improve it. Learn to link your PCB design to the schematic. You will be surprised at how quickly you can become proficient by doing this.

    Mark
     
    Treeman likes this.
  9. Veracohr

    Well-Known Member

    Jan 3, 2011
    549
    75
    Honestly an exponential converter is not that difficult until you get into precise calibration and temperature compensation. The designs on MFOS are a bit overkill for a starting step, he likes to provide a lot of external control options because his designs are based on a modular concept. Tou could easily start with a simple design and get a roughly correct control voltage/octave response, then play around from there.

    I found this useful to explain the exponential converter:

    http://electronotes.netfirms.com/s019.pdf
     
    Treeman likes this.
  10. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
  11. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    The average musician can tune their instrument to within .5 Hz of true pitch. The average musician can pick out an out of tune instrument in a band while playing a song when that instrument is just a few hertz high or low.
    The reason the music industry went to computer based synthesizers is that open loop VCOs could not hold true pitch over 4 octaves.

    Mark
     
  12. Treeman

    Thread Starter Member

    May 22, 2014
    158
    15
    And I thought I was just an average musician Lestraveled.......!
     
  13. Treeman

    Thread Starter Member

    May 22, 2014
    158
    15
  14. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Oops, I mixed that one up, but that is the right one. I use it all the time.

    Mark
     
    Treeman likes this.
Loading...