[sdiy] Drone Synth

[Scott Gravenhorst]

I know! I know!  You could use Spiral Waveforms!

But seriously...

It sounds like you don't need voltage control, so a 555 would work, however, look at the ICM7555
(and equivalents), these are CMOS and do not dump noise onto the rails like the bipolar 555 does. 
4024 works fine for a divider, just make sure the 555 (7555) runs from the same rails as the 4024.

4046 works for an oscillator too, but as you say, square out unless you use a quad opamp package
per oscillator to grab saw.  Then there's the Schmitz 4069 VCO, I think you can make a dual
oscillator out of this one by eliminating the PWM stuff.  Also, if you're not interested in voltage
control, the charge current can be provided with a simple pot to ground instead of the current
source.  HOWEVER, doing this will cause the output waveform to be an exponential charge voltage
curve (standard RC charge).  This is also true of the 555/7555 idea (with a resistor instead of a
current source).  To get true sawtooth, you'll need a current source per oscillator.  One of the
nice things about the Schmitz 4069 is that it's output is already buffered.  To grab the cap charge
waveform of the 555, you'll need an opamp, preferrably a JFET input type.

Steve Allen <snd_audio at yahoo.com> wrote:
>
>Hello All,
>I'm looking to build a module that will be used to generate a 
>drone tone to under current the main theme in a musical pieace. 
>I've looked at using 555 timer to CD4024 divider, a dozen of 
>those would be cool, but not very flexable once tuned up. How 
>about CD4046 PLL's using the divider scheme, more flexable, but 
>only square waves. Hum....... A bank of Rene's CMOS VCO's 
>........ a little complex but very useful. Any ideas? Hope I'm 
>not being too vague or.... well, never mind. Any and all ideas 
>will be appreciated. 
> 
> Thanks,
>   Steve
>
>
>---------------------------------
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