THIS PORTAMENTO CIRCUIT IS SUCKS!!!!! I created this circuit really early on before I understood input and output impedance. for a far better circuit. please refer to my new post
HERE HERE HERE HERE HERE HERE GO HERE THIS IS BETTER
A while back, I found a simple post on Linear portamento. it's here. It was a simple enough circuit but without the resistor and capacitor values, I couldn't get it to work. I tried a bunch of shit and eventually figured it out. It works like a charm--except the fact that it will sometimes--unexpectedly--but probably when I'm connecting or disconnecting the module-- it will "burn up" the LM324 quad amplifier chip I've got inside it. I added a resistor on the output and that may have done the trick, though I have been extra careful with the module. In reflection, the addition of the 1k resistor to the output may have adversely affected the module and there is probably a better solution. anyway, build at your own risk. I am considering, the next time I build the module, adding an extra buffer on both sides of the circuit. or perhaps using 10ohm resistors/capacitor set up to limit the amount of current allowed into the circuit all together. Keep in mind that I'm an amateur, here's what I built.
These values made the schematic work, there maybe other options that work as well. Make sure you use a bi-polar capacitor. also, it may be hard to see, but there is a switch that connects from the right side of the 1k resistor and the two diodes facing in different directions. They should be connected to a SPDT with center off (ON/OFF/ON) switch. The switch enables the asymmetrical aspect of the portamento, so it sides only when ascending or descending between notes.
What isn't pictured in the schematic is the 1k resistor I added to the end of the output. It's not in the schematic because like I said before, I want to try something different next time.
I suggest trying it out on a breadboard first. I do it with every circuit I make.
I built this module before I'd tried etching a PCB. Turns out, its really easy to etch a PCB and I probably won't be doing these perf board set ups anymore.
The module is top row, far right. It's a dual module, dunno, just because.
this pictures was taken later, as you can see, I have more modules now
Here's a Demonstration of the module with a synthesizers.com oscillator. Sorry that you can't see my fingers turning the knob or flipping the switch, but you get the idea. ha ha.