Electronics: ramps and oscillators

Andrew Booker 2007-09-22 15:12:46

The item in the picture is my handiwork. I've always loved the look of circuit boards and electronics, doesn't matter what they do. And recent talk of theremins has tempted me back into the archaic world of macro-electronics.

Back during Pulse Engine a few years ago, I spent months and months trying to put together distortions and filters and bits and pieces, almost none of which I used in the end, all now hibernating in shoe boxes in the attic.

I'm not doing audio effects for the moment though. Right now I'm about half way through building a voltage ramp generator and oscillator. It produces a varying voltage between zero and 5 volts, like this: I press a button labelled up, the output voltage begins to rise from zero to 5V. I press the up button again, and the voltage is held where it is. I press another button called down, and it falls back towards zero, unless I press down again, which holds it where it is. Also, I can flick a switch so the when the voltage falls to a minimum, it flips direction and starts rising, similarly when it reaches a maximum it starts falling... in other words it's become an oscillator. As well as the buttons and oscillator switch, I want controls for the ramp speed, the switchover thresholds and rise/fall time ratio.

I'm using CMOS 4000 series logic gates and op-amps. These are components I was buying 25 years ago. Amazingly you can still get a lot of them at Maplin, or RS for the more exotic bits and for shopping from a vendor who actually has any items in stock. Making things with discrete components like this is nearly as low-tech and cumbersome as using individual transistors. Or valves. Or issuing verbal instructions to a utilities company call centre the other side of Newcastle.

The chip count is 5 so far (though I can make two units with only 7 by sharing unused chip functions). When I've finished it I'll probably put up the circuit diagram. Then, if you know anything about electronics, you can see exactly why it took 4 op-amps (LM324), two latch flip-flops (4013), two schmitt inverters (40106), an XOR gate (4070) and an analogue switch (4016) to make an oscillator, when you can make one of those out of a single op-amp. And if you don't know anything about electronics... you're probably doing something more productive or recreationally beneficial than I am.

Why am I using analogue technology that's as old as me when I have a laptop that could probably do all of this if I bought the right software? It's because I play the drums. I can't type in instructions into a laptop when I've got two sticks in my hands. I've been using the laptop for 18 months and there are whole sound palettes and approaches that are completely out of reach because I just cannot operate them live.

So what is this ramp generator oscillator thing for? Well, I've got some voltage controlled filters that I've never used. I also wouldn't mind a tone generator for theremin-type device. Those both involve fiddling with more electronics and restoring some unused Pulse Engine projects, but there's one immediate use I can put this to that will help unlock a lot of the MIDI/laptop potential. An expression pedal.

There is nothing clever in an expression pedal, just a standard potentiometer with three connections: ground, 5V supply and control voltage. So I can plug my ramp/oscillator into the control voltage, and I have instant hands-free expression. I have expression pedal inputs on the PD4 effects unit and the SPD-S pads. The pads are MIDI-ed up to the laptop, so I can start controlling some of the funky ring modulators and wave modulators, the kinds of effect that totally wreck any signal made up of musical notes, but that do truly wonderful things to idiophonic sources like drums, even electronic ones. Especially electronic ones.

I will almost certainly not have anything ready for Tuesday's gig, but the whole effort has at least encouraged me to dig up an auto-wah distortion I built a few years ago and start using it on Nick's bass.

By the way, if anyone knows of a piece of equipment on the market that does the same as my ramp/oscillator specification, and that has probably been on the market since the mid 1970s... I'm not interested. I'm having far too much fun staring at my finished mini works of art and sniffing solder flux fumes.

8th gig: Tuesday 25 Sept 2007 at The Plough, E17 << | >> Expression pots and hits