[sdiy] More about the Aries VCO

[Ian Fritz]

At 04:04 PM 6/14/2004, JH. wrote:
>Now that I know the internals of the expo onverter, I've taken a closer look
>at
>the whole thing.
>
>This CA3080 based schmitt trigger is very clever! Must be pretty fast *and*
>precisely bouding at fixed level without saturating.
>(Does anybody know at what current it is working, i.e. the value of the
>resistor at pin 5 of U4 ?)
>
>I still wonder if it is *that* fast (and if the transitors have such low
>rbb) such that
>it doesn't need any HF tracking compensation ?!

I haven't looked at the Aries, but the 3080 as Schmitt trigger was used by 
Bernie in the ENS-76 series.  See EN#75, p. 10, or the builder's 
guide.  The integrator is a 3080 driving a 1 nF cap buffered by a 3140. The 
Schmitt trigger output is diode clamped.   There is no hf 
compensation.  The tuning wasn't measured to high precision, but it looks 
like it goes sharp (!) by 0.5% at the high end (24 kHz).

    Ian