portamento circuit

[gstopp at fibermux.com]

     Yes publish it - will it fit as an ASCIImatic? Let's compare notes. I 
     have made linear/exponential switched glide circuits. Usually what I 
     make is two op-amps, in a row, with the R/C in between them. The 
     second op-amp is always a buffer, but the first is switchable between 
     a buffer (for exponential) or a comparator (for linear). The (-) input 
     of the first op-amp has a SPDT switch between the outputs of either 
     the first or second op-amp. Works great.
     
     However one thing I've always found is that the glide time in linear 
     mode seems subjectively shorter than the glide time in exponential 
     mode. In other words, if you set the linear glide time to some medium 
     value, then flick the switch to exponential mode, the glide becomes 
     very long. This of course is due to the fact that linear glide times 
     depend on how far apart the notes are, whereas expo glide takes the 
     same amount of time no matter how far apart the notes are. Therefore 
     in expo mode it can be thought of that the notes are always the 
     maximum distance apart, no matter how close they are to each other.
     
     The only way around this I can think of is to use a DPDT switch and 
     switch in a larger capacitor when linear mode is selected. any 
     thoughts?
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: portamento circuit
Author:  Haible_Juergen#Tel2743 <HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de>
at ccrelayout
Date:    4/22/96 6:20 PM


Hi!
     
I have built and tested a little portamento circuit.
It's nothing special, only that it has minimum part count, 
and you can switch between  off / linear / expo with one 
single on-off-on switch which alters the feedback path from 
one opamp to two opamp stages.
If there is some interest, I might post or mail or upload 
some hand-drawn GIF.
     
JH.