[sdiy] 4046 in VCOs (was Hi frequency VC clock)

[Matthias Herrmann]

Haha, yes!
The 4046 was not intended to be used as an audio VCO. And this was reason enough for Thomas Henry to actually try and do it, I guess. I did other weird fun stuff as well.

BTW when breadboarding and beta-testing the Thomas Henry 4046 VCO we found that the NXP worked best (about 5  Octaves), whereas the TI never met the requirements. We simply did not even get one octave out of it. And the datasheets actually tell this IIRC.

Cheers,
Matthias


> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
> chris
> Sent: Wednesday, June 21, 2017 12:21 PM
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Hi frequency VC clock
> 
> To be honest, I never really understood why people resorted to use a
> 4046 as a stand-alone oscillator in the first place.
> That's not what it has been designed to do. Ok, it *can* be used like that, but
> in the intended PLL usage, the absolute frequency isn't determined by the
> osc intself but some input frequency, usually divided.
< snip >
> 
> Chris
> 
> 
> 
> On Wed, 21 Jun 2017 11:03:02 +0100 Tom Wiltshire <tom at electricdruid.net>
> wrote:
> 
> > They're all "good" in the sense that they do what they say on the data
> sheets. It's just that the data sheets vary between manufacturers, and also
> leave out many significant pieces of information. Notice, for example, that
> the datasheet doesn't actually provide a equation relating the component
> values and the VCO frequency. They focus much more on the linearity, but
> not the actual frequency. Makes sense for a PLL, perhaps, but not so good
> for us.
> > I did find that Texas Instruments chips were more linear than NXP ones.
> This was discovered by testing a couple of each and writing down a series of
> data points and then getting the computer to generate a line of best fit.
> >
> > I was looking for something that could provide a couple of octaves of
> exponential frequency modulation at 8MHz for top octave generation.
> There's an old thread on here "4046 VCO overclocking a PIC" if you want to
> find it in the archives. Some manufacturers versions of the 74HC4046 claim to
> be able to go to 10MHz, so those were the ones I chose. I was using a
> simplified variant of the Thomas Henry exponential control. What I found
> was that the actual frequency range is extremely variable between individual
> chips, and is even worse between manufacturers. For something that
> needed to be tuned to a musical pitch, this was hopeless.
> >
> > I still think that what I was trying to do should really be possible, but I
> wasted quite a bit of time on it and got nowhere, so eventually I got
> discouraged and gave up. I might go back to it at some point.
> >
> > Tom
> >
> > On 21 Jun 2017, at 00:03, mark verbos <markverbos at gmail.com> wrote:
> >
> > > I'm using a Texas Instruments one. It's SO16. I hope I can make these
> work, because I bought a full reel of them!
> > > Which brand are the "good ones"?
> > >
> > > Mark
> >
> >
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