30 years later...

[Christopher_List at Sonymusic.Com]

  Mitch, who isn't a dj or a washer/dryer, said:
  > how about having 3 oscillators, 2 of which would produce different
  > waves (at the same freq), and would be controlled by the third via
  > a flip flop thing (i don't know the technical term for it) so that
  > after one cycle, it would alternate between the two waves? i.e.:
  > you'd have say, a square wave for one cycle, and then a saw wave
  > for the next, and it would flip flop between the two every other
  > cycle. OR if you had enough oscillators, you could switch between
  > 3 or more waves, and maybe even have one at maybe half or double
  > the original frequency.

  Note that unless you want to do the frequency halving/doubling with waves
  that're NOT square - you only need one oscillator - as most VCO's have
  built-in wave shaping circuits to get the different wave shapes. In fact,
  a fun experiment for new waveforms might be to mess around with these
  wave shaping circuits in something like the EN Tri-Square VCO.

  What are some REALLY simple changes one could make? Just thinking off the
  top of my head here (note this is for those who know the circuit and know
  electronics better than I - I'd do the experiments, but I'm sitting at
  work right now!)...
  1. The tri->sine converter uses a 3080, with a fixed current into the
  control pin. What would happen to the output if the current varied - by
  varying the voltage? In other words, instead of connecting the 220K
  resistor to +15v, connect to the tri-wave output (or something else)...
  2. The sine wave output buffer is a current->voltage converter - this is
  basically the same thing as a summer - it would be trivial to sum the
  sine wave with any of the other outputs...
  3. (This one is a little more involved) Throw in an extra op-amp and some
  transistors (to make an "AND" gate) - and you could make the comparator
  for the square output into a window comparator - thereby doubling the
  frequency of the square wave. Just set the window to +2.5v and -2.5v and
  you'll get a perfectly spaced pulse on both the rising and falling parts
  of the triangle wave cycle. This might do some funky stuff to the PWM and
  saw outputs... This could be switched on or off, and if the square wave
  out were driving a flip-flop or counter to create other wave-adding
  effects you'd change a lot by switching it to normal or double freqency
  (especially if the counter had 3 or 5 steps).

  Might play around with some of these tonight (although I'm moonlighting,
  so I might be working late)

  As has already been stated - the best (most interesting) results will
  come from a wave that changes from cycle to cycle. As far as I can tell
  this requires a flip-flop or counter. An obvious choice for something
  like the "wave switching VCO" would be the CD4016 quad switch with a
  CD4017 counter - because it's output is decade, not binary, so only one
  switch is on at a time and one switch is always on. OTOH, if you used a
  binary counter, you'd get weird combinations of waves being added
  together (I guess the output would need to be attenuated by 50%).
  For example;
  Bit 0 Low = Square
  Bit 0 High = Saw
  Bit 1 Low = Triangle
  Bit 1 High = Sine

  Count 0 = Square + Tri
  Count 1 = Saw+Tri
  Count 2 = Square + Sine
  Count 3 = Saw + Sine

  - Does anyone have any suggestions for getting the wave to change
  (repeatably - not randomly) cycle to cycle in some other way that would
  not require any extra chips?

  This is kind of a fun topic - even though (as was already stated)
  changing the wave shape of a raw tone at the VCO in these minor ways
  doesn't really take you too far :)...

  - CList