Thursday, January 31, 2013

Asymmetrical Linear Portamento

UPDATE!!!!!! 8/30/13
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 


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 oscillator.  Sorry that you can't see my fingers turning the knob or flipping the switch, but you get the idea.  ha ha. 

1 comment:

  1. I haven't burned up any chips since I added a 1k resistor to the output.