30 years later...

[Magnus Danielson]

> 
> 
> 
> 
>   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.

Some like Rick Jansen has proposed in one of his VCO drawings?

>   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)

Don't burn to much silicon... not good for ya' :)

>   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?

Well, by picking an 4017 you'd could make a simple 1, 2, 3, 4 step thing no
problem, so you could go square, tri, saw, sine, quare, tri.... and other
things would also be easy to think up (like 2 or 3 waves). It would also be
simple to make it a little more variable so that you could have a swicth matrix
of 4 x 4 so that you migth select which combination of waveforms you want for
each step. Still keeping to a simple circuit you could go for haveing pots
instead of switches. You will need to feedback the 4017 to it's RESET to lock
it to 4 steps, but that's simple.. moveing the output used for feedback will
of course change the number of steps.

I think picking up a 4016/4066 and 4017 and possibly an op-amp for trigger
wave shapeing is a fairly cheap thing in itself. An output buffer could be 
worth
it thougth....

>   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 :)...

Hm... I have the instinctive thougth that what you basically get is a mixture
of them both with a small addition of amplitude of fc/4 as base since this is
the new real base frequency for the waveform you get... however, it's wierd
enougth and migth be worth trying... if it turns out interesting or not does 
not
count in... haveing fun and doing wierd stuff does :) :)
As long as you tries, it's OK :)

Keep Waveshapeing!
Magnus