Colour for Beginners: A Simple LED Clipper February 27, 2015 12:34

Welcome to the second month of our "Colour for Beginner's" series, where I, Chris, DIYRE inventory manager and electronics beginner, build a circuit on the Colour Prototyping PCB.

For this month’s circuit I decided to make an LED clipping distortion. The decision was inspired by the silver light left of the moon and a few cups of coffee. It wasn’t a long conversation; I suggested 3 circuits I was interested in doing to my friend Richard, and he said I should do something simpler like a diode clipper that used LEDs.

“But what about this that and the other thing?” I said.

“You know it will light up, right?”

“... whoa.”

A question for a question and I was on my way! Peterson liked it, too. He was all like, “Where were you all last week?” and “Get back to work!” He’s a funny guy.

So I got to work. I looked at these "Tone Clipper" circuits from AMZ-FX for the bulk of the design:

I thought it was neat that you could clip the highs and lows differently, by doing parallel high- and low-pass filters. Then I had another thought, that maybe I could use the RGB LEDs we use in the Colour Palettes to do the clipping, sending the highs through the red anode and the lows through the blue anode. Then, depending on how bassy or trebly the signal was, it would blend to make different hues of purple. Purple is my favorite color of all time, sometimes.

Since RGB LEDs only have four pins, the three internal LEDs all must share a common anode or cathode. And we only stock ones with a common cathode. This meant I couldn’t clip both the positive and negative portions of the wave using only 2 tri-color LEDs, which I thought would be neat. So, for the opposing diodes (to clip the negative portion of the signal), I just used two green LEDs.

Peterson suggested that via the Colour Designer's Toolkit, it would be a good idea to buffer the input and output with a dual-opamp. So I did that.

Here's my basic circuit:

I soldered the thing together and, to my surprise, it worked! I even managed to include some pots that actually do nothing. Impressive, no? I left those out of the Upverter Schematic as I considered them more of an aesthetic touch. Feel free to add your own superfluous components to anything you want! I intended the one pot to be a mix control, but I forgot the voltage divider part that would have made that pot do something.

This was a super satisfying circuit to make. It has a lot of customizability. You could change the cut-off frequency of the filters, or use different combinations of diodes for different clipping behavior. My original design had clumps of hair in place of the diodes for that hair-burning sound.

The distortion of my circuit isn’t very intense, as I didn’t do enough to overdrive the circuit, but it does clip, check it out:

And when it clips, it lights up!

Anyway that’s all for this month. Catch you next time!