[sdiy] VTL vs. H11F

[Tim Stinchcombe]

> lanterma at ece.gatech.edu wrote:
> > IIRC it didn't do that vactrol ringing thing - it responded much 
> > faster. So it was definely its own thing.
> 
> Do vactrols "ring"?  What part do they store the energy?  Do they 
> exhibit significant inductance or capacitance (or both)?  I 
> thought they 
> were just an LED and a cadmium-sulphide cell.

Ah, one of my pet peeves! Short answer: No. I regard this as a
misuse/confusion of terminology that seems to have grown up over the last
few years, mainly (I suspect) due to the resergence of some older Buchla
circuits which use vactrols, in particular (again I suspect) the low-pass
gate. These of course are fabled for producing the famed 'Buchla bongo'
sounds, which as far as I can tell arises because the lowpass filter closes
slowly due to the lag in the vactrol's response, giving the characteristic
'hollow'/near-clangorous metallic-type sounds reminiscent of ring mods etc.,
hence the reason (I suppose) for calling it 'ringing'. But of course this
has nothing to do with the usual resonant-filter-type-effect normal-use of
the term, but it has now been conflated with that meaning, so there now seem
to be a lot of people who think that there is some mystical ju-ju associated
with vactrols because they 'ring', and hence any circuit with them in 'must
be good'. [/rant]

(And I apologize in advance to Aaron, I don't mean to single you out! I
could also point to several posts at a now-defunct Yahoo group where
vactrols are touted as having this fabled property... Google 'ringing
vactrols' or 'vactrols ring', and you'll get a taster. And near the top of
my 'things to do next' list is a lowpass filter which is bongo-capable but
does *not* use vactrols, to prove this very point!)

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk
www.timstinchcombe.co.uk