[sdiy] new schematic posted

[harrybissell]

You could add the LED at will... and a parallel cap would work
but it will pop when you throw the switch because the caps will be
at different voltages. I think you could force the caps to the same
voltage with another opamp...  mebbe who cares ???

H^) harry

Peter Grenader wrote:

> Two things you might want to consider, always nice in a lag:  stick an LED
> in at the non-inverted output -and- how about a switch for parallel caps
> which increases the value at AR2 (range)?
>
> should I shad up now? (Magnus says yes, always....)
>
> ha!
>
> - P
>
> harrybissell wrote:
>
> > Hi Ingo...  (inline)
> >
> >
> >> Nice circuit. I must confess, it took me a while to find out why the
> >> output of AR3 is tapped off *after* the diodes and not directly from
> >> the opamp's output. This is to compensate for the diode voltage drop,
> >> right?
> >
> > right.
> >
> >>
> >> But doesn't this cause some interaction between the attack and the
> >> decay pot if the shape pot is not in one of its end positions? As I
> >> understand it, one one of the diodes conducts at a time. Say, the
> >> attack diode conducts and the attack pot is set to some high
> >> resistance. Isn't there some voltage fed into the integrator via R9 and
> >> R10 and the decay pot? Unless the shape pot is in an end position, in
> >> this case this path would be shorted to ground or virtual ground. But
> >> if the shape pot is in center position, R9 and the two halves of this
> >> pot form a voltage divider. So the decay pot would have an influence on
> >> attack too.
> >
> > Hmmm. I have not noticed any interaction.  Both sides of the shape pot are
> > at ground... The worst case would have to be with the pot at center
> > rotation...
> > each side would be 5K... in parallel that is 2.5K to ground.  The 20K /
> > 2.5K
> > divider would limit the effect of feeding back through one 20K... past the
> > 2.5K to ground, through the other 20K... and through whatever remains of
> > the decay pot.
> >
> > You could bring the resistor levels up (proportionally) and the effect
> > would be still
> > less... but it may be that they do interact a little. I'll try and look for
> > it.
> >
> >> Another question, as I see it, in linear mode (wiper of shape pot at
> >> ground) AR3 is overdriven (no local feedback). Can't it latch up?
> >
> > I suppose it could... but there is always the feedback from the integrator
> > as well.  I've built a log of linear lag circuits with this technique...
> > and have not seen
> > a latch up.  If you were going to have one, it would probably be at some
> > negative
> > input voltage (imho).
> >
> > Choosing a different opamp could cure that if it was found to be a
> > problem...
> >
> > Thanks for the comments !
> >
> > H^) harry
> >
> >