Re: [sdiy] VCO and expo converter question

[Scott Gravenhorst]

=?iso-8859-2?Q?Roman?= <modular at go2.pl> wrote:
>Well, it's simple CMOS inverter, 2 transistors designed to work 
>fully closed or open, where nobody cares for their cutoff 
>voltage, leakage and temperature dependence. I simply wouldn't 
>call it a stable analog component. I'd expect big temperature 
>drifts, and poor EMI immunity. However, I have no experience 
>using 4069 in analog way, I only have strong feeling this is way 
>out of "precision" league. 
>
>So you say 4069 VCO core works as good as opamp one?

I have built this little VCO and IMHO, it is quite good.  I also 
use an LM13600 tri/square VCO as well as the 555 VCOs in 2 FatMan synths.  
This whole system, i.e., all of my VCOs track each other as well as against
good quality digital synths.  This is true also of long term in that
I can use the FatMan containing these VCOs and all are in tune with
each other and the digital synths as much as 2 weeks later.  These are
linear VCOs and I do not notice any problems with temperature.  I used
to play in a band that practiced in a garage.  During the summer it would
get to 100 degrees F and after having warmed up in the morning (70 degrees)
I rarely had to touch the tuning knob.   

In my opinion, this is a good sawtooth VCO design that makes excellent use
of the unused inverters by providing a PWM output as well as the saw.


>Roman
>
>---- Wiadomo¶æ Oryginalna ----
>Od: René Schmitz <uzs159 at uni-bonn.de>
>Do: Roman <modular at go2.pl>
>Kopia do: ryan <destrukto at gmx.net>, synth-diy at dropmix.xs4all.nl
>Data: Mon, 24 Nov 2003 11:21:28 +0100
>Temat: Re: [sdiy] VCO and expo converter question
>
>>> transistor pair (in human language precision=expensive), then why
>>> bother using 4069 as integrator and schmit trigger. CMOS can't give
>>> you the stability that your new expo converter provides. I'd change
>>> it into standard opamp integrator and comparator. But anyway it's
>>> only my sick opinion. 
>>
>>What makes you think that it wouldn't be stable?
>>
>>Cheers,
>>  René
>>
>
>

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