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Propsynth D - a 6 voice polyphonic synth with Propeller chip — Parallax Forums

Propsynth D - a 6 voice polyphonic synth with Propeller chip


here is my latest development.
A 6 voice Synth, using the Propeller Chip

It is a DIY project, included all files/schematics to build the synth.

habe fun

PropB3 / H.Bollig


  • Thanks for sharing! I can't wait to try this. I've been looking into music synthesis more and more. I'm not musical at all but the way sound waves interact to form what we hear always fascinates me.
  • +1 what mindrobots said
  • Ach! I just looked at the webpage! It is a beautiful project but being in all German, it will certainly challenge my 40 year old High School German skills!! :)

    Luckily, schematic and parts list are mostly universal.

    Even if you aren't interested in synthesizers or music, you take a look at this project. It is very well done and complete!
  • TorTor Posts: 2,010
    That looks great! Want.
  • The project looks great, thank you for sharing with us all.

    NOTE: We can use Google Translate to convert the web page from German to English
  • Translation:

    PropSynth D

    A 6-voice synthesizer with a propeller microcontroller & FV-1

    Prototype PropSynth D

    Hello to all music enthusiasts.

    After the Hammond organ and the String Keyboard simulations based on a Parallax Propeller, the step to build a synthesizer was the logical consequence.
    This new development is a classical polyphonic 6-voice synthesizer according to the well-known model: Oscillator-Filter- VCA, also known as subtractive tone generation.
    This time I did not want to emulate a very specific synthesizer, but to develop a "normal" sound generator, which cannot do any more than many other synths, - but with a standard processor not developed for this purpose.

    • 2 oscillators per voice / 6-voice polyphony
    • 10 Wavetables for the oscillators
    • Filter, (4-pole lowpass, 2-pole lowpass / highpass / bandpass) with resonance
    • ADSR Generator for filter curve
    • ADSR Generator for Amplifier Envelope (VCA)
    • LFO for filter modulation
    • LFO for Vibrato
    • Noise generator
    • Various chorus effects
    • Hall device
    • 3-band EQ
    • "Half-analog" operation with potentiometers in a parameter matrix
    • Preset memory, 32 programs
    • LED display
    • Control via MIDI controller
    • Stereo outputs

    Controlled via MIDI, the propeller is enough for 6-voice polyphony. The mainboard is only 200 * 100mm and contains all components inc. the control elements. The one-sided PCB is easy to build, since only components which are easy to obtain are used, SMD components (which we unfortunately can not do without) are installed via adapter, and with 1.27mm pin spacing can be easily soldered by hand.

    But before we get to the nuts and bolts, here are some legal notes:
    The author accepts no liability or warranty for damages which arise directly or indirectly with the use of this project.
    The PropString is intended for private use only. A commercial exploitation of the circuit, software or parts thereof is hereby prohibited.

    Here is a sound demo (everything comes from the PropSynth D - no additional effects added)

    The Leslie Organ
    Jupiter Strings
    DX Piano
    Jumpin LFO

    My wishes, wants and ideas are rising: - (again)!
    Originally, this project should be a classic hybrid analog synthesizer, ie digital oscillators and analog filters, etc. A 4-voice model was almost finished, but when I added up the numbers of capacitors, resistors and IC's, I rejected this and devoted myself to the purely digital solution. It was supposed to be a weekend project, and not a life task.

    Hardware at the limit :
    DSP functions without multipliers, sounds like "Rally Paris - Dakar on a bike" and is actually not possible, and on top of this the propeller can only address 32 KByte. This is not much for firmware, waveforms and memory.
    Relief comes in the form of the FV-1 chip. In addition, the propeller runs not at 5MHz but is "overclocked" at 6.4MHz.

    Some of the PropString design was used, like the FV-1 effect processor. Controls using potentiometers and switches as with the PropString I found nice to use, but with the number of parameters a large number of controls cannot be avoided.
    This time, too, a display, for parameter control, should be used. I decided to use the "Parameter Matrix", a concept consisting of pushbuttons for line selection and potentiometers in the columns (which was very beneficial in the development because new parameters / functions simply fit into free spaces in the matrix).

    The Synth can of course be completely remote controlled via MIDI. The whole circuit fits exactly in Hammond 1599-HSGY housing.

    Etching - soldering - programming
    All the necessary documents for construction cab be found here. Propeller, FV-1 chip are also relatively easy to procure in Germany. The D/A converter is available on EBAY.

    What you will need, however, is a burner for I2C-EEPROMS. There are two EEPROMS to burn. A 512 (64Kbyte) for the propeller, and a 32(4Kbyte) for the FV-1 processor. On the internet are many building instructions for simple I2C burners. I used PonnyProg. The required hardware is easy to build, and the software is free.

    Wiring diagram: PropSynth Schaltplan.pdf
    The complete building instruction:
    Notes and controller assignment: Notes.pdf

    Mainboard Mainboard & Control Panel
    PCB backside with voltage regulator & wire bridges Parameter matrix

  • I can't seem to resolve ( seems to be delegating it back to .de's root servers), but the project sounds interesting. If and when we see a P2, I'd like to use the faster processing and what seems to promise a hardware multiply to implement a hybrid FM/waveshaping synth (I used my FM synth project to push the P1's integer math capabilities without using a DSP). Your project sounds like it would be a great intro to the FV-1 for me.
  • pik33pik33 Posts: 1,051
    edited 2017-04-05 12:12
    I can open the link without any problem

    Edit - now (April 5) I cannot.
  • I like his control surface a _lot_ more than mine! :) This looks like a really cool project
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