Help with synth keyboard

Discussion in 'The Projects Forum' started by djex, Feb 28, 2011.

  1. djex

    Thread Starter New Member

    Feb 26, 2011
    I have been playing around with various oscillator circuits lately and soon will be trying to put them together into a small synth.

    Now I want to be able to play notes with the oscillator. At the moment I have two 555 timer square wave oscillators that are adjusted by a pot for the pitch. Now I know 555 timer oscillator circuits arn't proper synth material but I'm new to all this and it's a great learning project for myself.

    Id love to be able to have a series of buttons that I could implement into a 2 octave keyboard and with each button is a different note in the octave. I read about adding resistors between each button in series to produce a different note but I read on a few sites that this would not be 100% accurate.

    So my question is what can someone recommend in order to get accurate notes from each key press. Now you may say why does it matter if its just a learning project, well for one I like to do stuff right the first time and secondly I'm an artist my self and improper notes would drive me insane :p

    I read about keyboard matrices but can't seem to grasp the concept of how they work. Would this be what I need?

    I plan in the near future implementing a few types of wave forms into my synth with a few op amps I manged to scavenge off some old electronics. Would changing the pitch of a op amp oscillator circuit be similar to a 555 timer by changing the resistance? Sorry if these are simple questions.

    Hope someone can help. :)
  2. bribri


    Feb 20, 2011
    a keyboard matrix can get pretty involved, especially if you want polyphony.

    for a mono-synth, a string of resistors is probably just the thing. just using 1% tolerance resistor values would be pretty accurate i think.
    if you started with 5% resistors to get it all working, you could swap each value out with a pot, tune to your liking, and then just pop in the closest value E96 resistor. it's also possible to cheat by trial and error combinations of 5% resistors to get to your ideal value.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
  4. djex

    Thread Starter New Member

    Feb 26, 2011
    Thanks for the replies. I'm going to play around with the resister idea you suggested bribri.

    Thanks for the link kermit2, should be helpful for the other components I plan to make for the synth.

    Just out of curiosity, how would one go about making a polysynth? I'm assuming then you would need a keyboard matrix to be able to play multiple notes at once? Also you would need a way to vary the pitch other then using resistance? For now I'm sticking with a monosynth but it would be good to know for the future if I decide to expand on my project. :p