UPDATE!!! 8/19/13 I just finished a newer version of this module. I changed some component values and ended up with a better version of this design. I also added in a gate activated on/off switch. it will be posted soon.
I was super excited when I found the Schematic for this simple but versatile portamento circuit. I Had an idea similar to this, a little while back when I was building the Ian Fritz AD/AR generator. I noticed then, even the Fritz AD/AR was similar to a simple lag circuit, and it put the idea in my head for a simple portamento with seperate controls for up(attack) and down(decay) slide. Nerds will notice right away that this can also be used as a simple envelope generator.
The original circuit can be found here. Below is the version I printed and made some modifications to. Also, I clearly spilled coffee on it. Since the schematic already used three op amps, I decided to go ahead and use a forth for the indicator LED, which is probably unnecessary, but turned out really cool. I thought it would be cool to have one led correspond to the attack and another correspond to the decay. I tried a differentiator op amp set up, comparing the input voltage to the output voltage. That schematic is in the bottom right hand corner.
I breaded it up and everything worked great except for, when the shape knob was at its most ccw point. It was doing this weird self oscillation thing. I rectified that by adding a 240Ω resistor.
I also added a bypass switch.
I design my PCB's in photoshop. I've been playing around with inserting pictures in the background of my PCB's, and I guess it's kinda my thing now.
1x LM324 (or any quad op amp)
2X 22uF electro caps
4x 1uF Tantalum caps (or any other higher value non-polar)
4x 1n914 diodes (or any switch diodes)
2x 10k pot
4x 1M pot
4x 1/4" jacks (6 if you include the inverted output)
2x spst switch (4 if you include the "long" switch)
4x regular leds
This is a Dual circuit.
I used 1uf Tantalum caps in my circuit because I had a bunch laying around, but you should be fine using any larger non-polar cap. I put an option in for adding a "long" switch, which would add more capacity and give you longer slide time but I ultimately found it unnecessary, but still the option is there. My final module has two 1uF caps for each of the two circuits. I also skipped the inverted output jack because I ran out of room on my module face.
I'm not gonna spend a lot of time explaining how the pots should be wired. if you can't figure it out by the schematic, then it's a skill you should learn. For the attack and decay pots, you add lag by adding resistance, so you'r going to want to solder one point marked "A" on the PCB, to the CCW pin of the pot and the other point marked "A" to the S (center) pin of the pot. Do the same for the Decay. The bypass switch points are labeled "b" on the PCB for bypass.
so, I've been doing this transfer thing for a little bit now and I get my best results when I use steel wool on my copper first. Also, don't have the iron on too high. I set the iron to just barely higher than the "polyester" setting. Even when I get a really good transfer, I still usually have to do some minor touch ups with a marker.
I also have this method for doing the acid bath. I put the board in a shallow tupperware container, add the acid, and put a pencil under the container. Then I use my finer to tip the container back and forth, causing the acid to wash over the board in a regular motion. I usually have a fan on too.
Try it, it work pretty well.
nothing to adjust once it's built. if you're super worried about tuning over several octaves, I'd use 1% resistors. I didn't, and I noticed the CV for pitch get's a little skewed at the far end. Call it character.
there's the PCB
Hit me up with any questions or if you spot any faulty information. I am an amateur. Here's a video of it in action. You're probably gonna want to full screen it, if you want to see the LEDs in action.