Glide circuit of the ProphetV

[Roel Das]

<snip>
> > And, when you use the 13700, you don't need the buffer, because you can
use
> > the one on the chip right?
>
> No... the darlington buffer can only "pull up" and has a passive
pull-down. so
> it can source lots of current, but sink is fixed... this would cause
asymmetry
> in the glide. The
> TL082 has a higher input impedance and symmetric drive current... very
good.
<snip>

Do you mean, use the TL082 at the bias input? This confuses me... You just
mean this is THE opamp to use after the cap, right?

However, I read Gene Zumchak's OTA primer, learned alot, thanks. But some
things still bother me about OTA's. How do you use the diode bias input on
the 13x00? The diodes don't have any influence when you don't connect the
input or something?

So, if I replace the 3280 with the LM13700, I do still need the current
mirror and the diodes?

I'd also like to add some control to make sure the glide is off for
portamento 0. Adding a trimmer before the current mirror, would only affect
the maximum glide time, so maybe a MUX to choose between the original and
the portamento output?

And one more common question, any reason why to use the 1N914 diodes here?
What criteria are used to select a diode? The current it can handle and the
junction voltage, or more (and availability, offcourse)?

Thanks

Roel