--- In Doepfer_a100@yahoogroups.com , "Doug" <dougc356@...> wrote:

>
> I thought of it more as a means processing the CMP out signal upstream
> of the LPF, for example, coming up with an alternative cmp strategy. I
> suppose if the LPF is just a mini A-171, then one could just bypass
> the entire LPF as you suggest and use the A-171 instead.
>
> I am still mystified as to why the LPF output leads to smooth output
> from the internal VCO, but causes jitter when going to an alternate
> VCO. It's as though the internal VCO has a built in slew or something.
>

hello dough,

i find that the a196 manual explains it quite well.
the phase comparator in the a196 generates a digital
signal, which is used to drive a linear vco.
the lowpass filter is there to smooth out this
digital signal and make it less jumpy, which leads
to a more stable vco output. since other vco's are
controlled in a different way (not by a digital signal,
but a continuous analog voltage), you won't get the same
results with "normal" vco's like a110 or a111. inserting
a lowpass filter at a different position in the pll would
just compromise the function of the module.
somebody please correct me if i'm wrong here.

best wishes

ingo