I’ve been learning how to draw schematics for the devices I make, and I’ll be publishing them here as I go.
(ps I’m a total noob at drawing schematics so please let me know where I’m doing it wrong, e.g. I don’t know how to represent a vactrol so I just put a shaded box around the relevant bits for now, ok?)
So what’s happening here?
As I kinda explained in the video on the other post, this machine takes an audio signal from anywhere (I use a sub out/control room out/headphone out from my mixer depending what I don’t need at the time) and amplifies it enough so that the changing velocity of the signal causes a big LED to pulse in time with whatever you’re sending it (rhythmic things work well but anything with an attack works.) The pulsing light from the LED is converted into resistance by an LDR, and this pulsing resistance controls the pitch of an oscillator which is outputting a fat-ass squarewave.
Another way of saying that: It goes “pew pew pew” like a sci-fi ray gun.
Hear it in action
THE DESTROYER has so far been used on one finished recording, my remix of NSU’s “Broken Mirror”. It kicks in at about 24 seconds into this preview. In this instance I fed it back into itself which makes it go a bit mental, but around 57 seconds in it calms down a bit when I apply the decay control. Overall, this example is way more random and squally than usual but it gives an idea of some of the ways it can be used.
- R1: 1K resistor, protects the LEDs
- R2: LDR (light dependent resistor) glued to D2 (see note 1)
- R3: 50K potentiometer, acts as a sort of envelope decay control
- D1: 3mm LED, optional (but handy) visual indicator
- D2: 10mm LED, glued to R2 (see note 1)
- T1: NPN transistor, I used a 2N3904. Amplifies the incoming audio signal.
- IC1: 40106 hex schmitt trigger, generates the output audio signal
- C1: 10uf electrolytic capacitor, blocks DC noise.
- C2 & C3: Capacitors, values to taste. (see note 3)
- S1: SPDT switch between C2 & C3
- S2: SPST switch to bring R3 in & out of the circuit
- J1: Audio input jack
- J2: Audio output jack
Notes & important stuff:
- D2 & R3 are combined to make a vactrol. First, use a file to (almost) completely remove the round end of the LED. Next, use a drop of superglue to fix the newly filed flat end onto the face of the LDR. Finally, use heatshrink or lots of dark electrical tape to wrap them in a lightproof cocoon. You may need to paint out the back end of the LED. The aim is that when the LED is off, no light at all from any source should reach the face of the LDR.
- Apparently all unused odd numbered pins on IC1 should be connected and grounded. I haven’t actually noticed this making any difference, but it might.
- The values of capacitors C1 & C2 define the frequency range of the output signal. Choose two (or more) capacitors of different values and switch between them (S1) to give the option of high/low pitch ranges. Larger capacitor values give a lower pitch range, start with something around 1uf. If you don’t want or need this option you can replace that entire limb with one capacitor to ground.
- R3 is a kind of envelope decay. It affects whether the output signal is cut off short with every pulse or left to carry on downwards until the next pulse. If you don’t want this option you can omit R3 and S2 entirely (but don’t, it’s pretty cool).
- Also the small LED D1 doesn’t do anything to the audio but it mirrors what’s happening inside the vactrol i.e. it shows you when an input signal is present, which can be pretty handy.
- All grounds are connected to 0v
I forgot to draw in a switch to turn it on and off. Just imagine one, right at the top, just below the “+9v”
Also, the part of the circuit built around the 40106 chip is based on Tim Escobedo’s “synthstick” oscillator (you’ll have to google it, his own site disappeared a couple of years ago). My friend Sean showed me how to build it and I use it as the sound-generating portion of a lot of circuits. It makes big fat squarewaves.
In the next electronics oriented post we’ll have a look at my version of the “synthstick” ribbon controller and have a closer look at that oscillator.
Leave a comment here if I’ve forgotten anything else (or for any other reason), and good luck.