VCO

[Synthaholic AKA The Shark]

Very good info, and thank you.  Actually, my application of the 4046
has an adjustable damping pot in the filter (I used the balanced T
type).  I know I'm weird, but I *like* the portamento and sproing
effect.  It adds a unique character.  The sproing makes it sound kinda
like a dijereedoo, the portamento causes a flanging effect during the
pitch change (when mixed with the driving VCO signal).

Bizarre thought occurs:  What about a simple VC-LPF as the loop
filter???

If my poor memory serves me, I think that the linearity point had to
do with using the PLL's VCO without the loop, simply as a high freq
VCO for clocking wave tables.  Although I still must try it for
myself, I've read in other threads on PLLs that 4046s make poor VCOs
(even for us linear folks).  I believe the comments there were that
it's linearity is only about 2%.  Clearly, when used as a PLL to
multiply freq or simply track an incoming signal, linearity isn't as
important unless you intend to use the PLL's output control voltage to
drive highly linear VCOs.  If the 74HC7046 or 74HC9046 are quite a bit
more linear, then I will want to try this.  Especially since I've
already been able to eek out more waveforms than just square.  Would
anyone have the linearity spec on these parts?

On Sat, 23 Aug 1997 12:38:11 -0500, you wrote:

>
>>>Any one test'ed the 74HC7046/74HC9046,a new design of the old 4046PLL?
>
>>The linearity may be bad with the 4046, but the real problem with the
>>'portamento' effect will be the loop filter.  If the filter is set too
>>low in freq, it will cause lag.  If set too high, it will cause a
>>'sproinging' over-under-over-under shoot problem.  the characteristics
>>of this may change slightly with better linearity, but the real
>>problem is the filter.
>
>The 470K/47K 0.1uF cap filter given in the applications manual is optimized
>for audio. Believe me I played with those values till I was blue in the
>face. The phase locked loops step nicely from two octaves below middle C to
>two octaves above using the above values for loop filter. Adjusting the
>main timing cap will give you better locking in low or high parts of the
>range. A good technique is to monitor the voltage into the VCO control
>terminal (pin 9?) and adjust the cap to get half the supply voltage at a
>frequency which is the center of your range.
>

- Scott Gravenhorst (Synthaholic)

Programming: The Ultimate Computer Game.  Unfortunately, you never win.
Hell: Windows 95, 16 bit apps and Banyan Vines

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