category archives: electronics

…and a fancy new theremin

(Actually I built this a few months ago but I’ve just recently made some modifications which kinda make it new again.)

As soon as I saw Moldover’s fancy CD case instrument I knew I had to make one. But not in a CD case – it had to be bigger, stronger, and more like a flying saucer from an Ed Wood movie.

And so:

Optical Theremin
Hear it in action in the last 30 seconds of this video.

What does it do? If you don’t know what a Theremin is, read about them here or watch theremin videos here. If you do know about Theremins then you’ll know that this isn’t really one but it’s a convenient shorthand for an instrument that you play by waving your hand through the air.

A true Theremin is controlled by playing the electro-magnetic field around an antenna – the amount of capacitance created by the proximity of your hand to the antenna determines the pitch – closer to the antenna for higher notes, further away for lower ones.

Lev Termen (AKA Leon Theremin)
Lev Termen (AKA Leon Theremin), inventor of the Theremin and international man of mystery.

In an optical theremin, on the other hand, pitch is determined by the amount of light reaching a light-dependent resistor (also called an LDR or photocell). That’s the little round thing at the left end of the device in the first photo. More light = higher notes so moving your hand closer to the LDR lowers the pitch and pulling away raises it.

I’m pretty sure this is the circuit I started with, taken from here, with my slight modifications described below.

Optical Theremin schematic

  • Q1 = 2N3904 Transistor.
  • Q2 = 2N3906 Transistor.
  • C1 = 0.1µF ceramic capacitor but for some reason I seem to have used an electrolytic cap. Not sure if this is a good idea or not.
  • PC1 is the Light Dependent Resistor.
  • The battery is 1.5 volts
  • The speaker is 8 ohms and is not optional. The circuit won’t work without it.

The first thing I added to this circuit was the momentary switch, just because it makes it more fun to play. I put it on the + battery lead. This switch is probably the most expensive component at about $10. I started with a much cheaper plastic one but it does get a bit of a hammering and could tell it wasn’t going to last long. YMMV.

Next, I added a fairly big capacitor to lower the range and a switch to bring it into the circuit when it’s needed. The reason I did this is so I can use it outdoors in the sunlight and other brightly lit environments. As it was, the pitch was just way too high in the daytime. The extra capacitor(s) to alter the range can go almost anywhere. I think I put it across the LDR. As with any of these things, try different values of capacitor until you find the range you want. I used 680nf.

The other way to deal with the sunlight problem is to put some really dark sunglasses over the LDR but I didn’t think of that until just after I’d mounted the switch :) Now that I think about it, a variable capacitor would be even better.

Anyone else using or making optical-Theremin-type instruments that I should know about?

a fancy new ring modulator

The twisted sounds I’m squeezing out of the drum machine in this video are courtesy of my fancy new ring modulator.

Ring Modulator

(The pick was for scale but I just realised the plugs make it pretty obvious)

What a ring modulator does – as I understand it – is take two audio signals and combine them by multiplication rather than addition. The resulting signal contains the frequencies present in the original signals, plus the sum of those frequencies, plus the difference of those frequencies. And another way of saying that is “it uses one sound to totally fuck another sound up”.

Results vary somewhat depending on what you feed it but typical results involve lots of weird overtones, hollow metallic sounds, and discordant, chiming, grinding, squealing noises. Cool. The “Dalek” voice on Dr Who is also a product of ring modulation, a steadily oscillating sine wave modulating a human voice.

In the case of the aforementioned video I’m using a sine wave to modulate the drum machine. Sine waves work really well and are a good place to start but you can also use one synth to modulate another synth or an oscillator to modulate a guitar etc etc.

Inside ring modulator

So what’s in it? If I’d known how simple these devices are I would’ve had one ages ago. If you want to make one like mine, here’s how, written for noobs like me.

Parts:

  • 2 x small centre-tapped transformers (I just used the smallest ones I could find at Jaycar, they were about 5 bucks each)
  • 4 x zener diodes (the ones I used are 0.3 3.3 volts, 1 watt. they say germanium ones are better, maybe any diodes will do? I don’t know and I don’t care)
  • 3 x 1/4 inch TS sockets

Really, that’s it. You probably want some kind of box to house it in, but that’s it. No power source needed, no moving parts, no switches and dials.

Assembly:

  • The diodes have a positive end and a negative end called the anode and the cathode. Don’t worry which is which but DO make sure they’re all facing the same way. You can tell quite easily by the markings. Solder them end to end in a square – anode to cathode, anode to cathode etc – this is the “ring”.
  • The transformers should have two terminals on one side and three on the other side. On the first transformer, take the two outer terminals of the three and connect them to two opposite points of the ring. Do the same with the other transformer and the other two opposite points of the ring.
  • Connect the two centre terminals (one from each transformer) to one of the 1/4 inch sockets.
  • Connect the remaining two terminals on one transformer to one of the sockets. Repeat.

And you’re done! Now connect two of the sockets to your instruments/sound sources and the other to an amp or mixer and modulate away. Any socket can be an input or an output but different configurations do sound slightly different.

Experiment and enjoy.

even more about plate reverbs

The other day I posted a new recording which made heavy use of my home made ghetto plate reverb.

The plate is now safely boxed up and mounted on the back wall of the house, and while I was outside tweaking it today I thought I’d better take some photos.

(click em for bigger ones)

reverb unit outdoors

When I go out to inspect the unit I like to play Also Sprach Zarathustra at high volume.

reverb unit outdoors

I made the lid in two parts for easier access. I think a hinged trapdoor might be even better though (later).

reverb unit outdoors

I’m still playing around with the placement of the piezos – I had them all in a row down the centre for a while but I think the crucifix configuration – top, bottom, left, right – sounds better.

reverb unit outdoors

The send and return cables – or input and output cables if you prefer – all run under the house to and from the studio.

reverb mixer and amp

The send is powered by an old stereo amp I found at the tip and the returns are mixed in the little passive mixer I built for, um, mixing returns. Still need to make some knobs for it.

Pretty happy with the ‘verb sound so far (which you can hear in action here and in demonstration here and here). Some sort of dampening system is the next step, with a motor control that I can operate from the studio.

That’ll have to wait a while though, so much to do etc, many different men to see about many different dogs.

new recording – over

Just finished mixing this song. It’s not the first recording I’ve made of it though, so some might recognise it.

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download mp3 (right click and save as)

The song is called “Over”. It’s here as a free download so pass it on, and it (or something very similar) will be on the soon-to-be-released Harmonica Lewinsky e.p. too.

The exciting part (for me anyway) is that it’s the most extensive use I’ve made of my plate reverb so far – the percussion, guitars and vocals are all running through it – and in fact I don’t think I used any digital reverb at all now that I think about it.

More geeky stuff about reverb soon. For now enjoy the song.

white collar 2010 – live mix, new toys

Once a year (at least) I re-mix and re-invent white collar criminal, a track I started work on in 2004 and don’t intend to finish. The first one was a zero birthday present for my godson, Rhythm, and they’re all dedicated to him.

This year’s version is a noisy, glitchy, live-in-the-studio jam on my drum machine with a ring modulator, an oscillator, a crusty old sampler, an optical theremin, and lots of echoes.

It’s unedited and I filmed it so you can see I didn’t cheat. The only thing happening unseen is the occasional tweak of the delay feedback on the desk, just out of shot.

The new toys are the ring modulator and optical theremin: the former is used throughout to warp the drum sounds via the Good Will Audio Generator and the latter makes an appearance just before the end of the clip.

But more about them later, it’s 2 am and I still have noise to make. Download the track(s) here.

good will audio generator

I briefly mentioned this piece of kit earlier:

tone generator control panel

A few months ago my mate Dangerous Dave gave me a frightening-looking piece of medical equipment about the size of a microwave oven. He said it was supposed to generate tones but when he’d plugged it in he blew all the fuses in his house (not sure how that works) so he thought I might like it.

“Tones?” I said. “Okay I’ll have a look.”

And I put it in the corner of the studio and there it sat, gathering smaller items onto its large flat surface.

A couple of weeks ago I finally had a proper look at it. I still don’t know exactly what it was and I forgot to take a photo before I dismantled it, but inside it there was indeed a sine wave / square wave generator, (pictured) with a range of 10Hz to 1000kHz (One Million Hz!)

Most of the rest of the microwave-sized case was filled with a big amplifier and some complex digital and analogue metering equipment. Some of it might still work (later) but something in there was badly shorted.

With a very small amount of tinkering and a couple of new components (switches, jacks and LEDs) I managed to get the noise-making part operating without the fuse-blowing part and it sounds like this (with echoes of course):

The first five buttons on the left determine the frequency range. The highest is 100,000 Hz to 1,000,000 Hz! (For non audio geeks: humans hear up to about 20,000 Hz on a good day.)

The last button switches between sine and square waveforms.

I took it out last weekend for a bit of a play at an outdoor dj thing I do at the market and it was a lot of fun. It now has a permanent place in my arsenal of audio weapons.

something to do on wednesday evening

Those of you in Auckland are encouraged to get along to this, beginning this Wednesday the 9th, upstairs at Handmade (the old Brazil) on K’ Road.

Experimental music, experimental instruments both acoustic and electronic, kind of an offshoot of the long-running Vitamin-S but perhaps with more of a rhythmic and melodic focus.

Come to play and listen or just to listen. I’ll try to get there too.

bending the alesis part 1

I’ve had this drum machine, the Alesis HR-16b, for about 15 years. I haven’t used it much lately because although it’s a nice machine which is really quick and easy to program and a lot of fun to use, it has to be said that the sounds are a bit too clean. It’s hard to get it to sit right in a mix, it always needs a bit of distortion or lo-fi filtering.

And with the easy availability of far more sophisticated software drum programming tools these days it just isn’t worth using drum machines for recording unless you really like the sound of them. And even then it’s usually easier to record the sounds you like and sequence them in a software environment.

I would, however, like to incorporate this machine into a live performance set-up. For one thing, I like to have sounds coming from multiple sources – rather than all out of the same usb port on the laptop, into the same channel on the desk, through the same effects etc – and secondly, like I said, it’s a really fun machine to use. Soooo…..

alesis drum machine

…. I was pretty excited to read this very informative thread which explains just how easy it is to warp the HR-16 / HR-16b to get a huge variety of distorted, gated, glitchy, modulated sounds. Oh Joy!

What I learned (from the link above) is that all of the sound data is stored on two 32-pin chips, and connecting any two or more of the pins on each chip to any other pin on either chip gives you the bends (so to speak).

I also learned to “stay away from pin 1 (program supply), 22 (chip enable), 24 (output enable), and 32 (+5V)”.

These are the chips:

alesis chips

And here’s what happens when you connect a few pins by poking screwdivers at them:

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download mp3

So the trick is to make some kind of switching system to make connections between the pins, preferably something a bit slicker than poking screwdrivers at them while the machine is running.

Most people who bend this machine seem to like a patchbay system, others use quite complex switching systems, usually built on the top of the machine which has a big flat space with plenty of room for sockets and switches.

There’s plenty of room inside, too – no trouble finding space for extra wiring. It’s a bit like working on an old car.

alesis board

For some reason (beyond my current understanding of such things) the data is identical on both chips so it’s only necessary to use half of the pins. This makes soldering a bit easier as you can just use every second pin, alternating between the chips, and still get all the possible connections.

From a comment in the same thread (above) I got the idea to do all the switching and bending in a separate box, so I’ve used one of those long connectors you find on the back of a floppy drive (which is exactly where I found it) and wired each usable pin to a corresponding pin on the connector.

alesis bending

Now I can use a flat ribbon cable and experiment in a separate box without destroying too much of the case of the machine until I know what I want to do. Also I can potentially build several different boxes with different switching systems so it keeps the whole thing nice and flexible. Also I can put the machine back together and keep using it as normal while I experiment with breakout boxes.

————————————–

As you can see, so far I’ve just been putting together other people’s tried and tested ideas but next comes the interesting part – coming up with some way of switching the connections. I haven’t given it too much thought yet but I do have the idea that some way of fading between connections and combining different bends in a smooth, fluid way might be fun.

Maybe something with LDRs (photocells)? I think I’ll start with pots and faders and see how I go. Any ideas appreciated.

innovation from moldover

Oh this is cool. Electro musician Moldover has released his album as a cd attached to a light-beam theramin. Check out the vid:

To find out more and hear the album go to moldover.com

what do i call these?

I was doing some experiments this afternoon with an aluminium lid, probably from a wok or some other large pan.

I’d noticed it made some quite nice noises when I found it the other day and I was wondering if it might be any use as a reverb plate. I’d always figured aluminium would be too soft for reverb but it rang out nicely when struck so I gave it a go.

wok lid drums wok lid drums

Turns out I was right – it was a terrible reverb plate. But now that I had it on a stand in the studio with a piezo attached I figured I may as well do something with it, and seeing as I couldn’t eat it, I hit it with a stick.

I was reading the other day about my friend Sean’s new pots-and-pans drum kit – which also uses piezos to pick up the sound. I also happened to have another one of these lids lying around, slightly bigger, so I wired that up too.

Sean’s using his for the sound of the pan itself and also as a switch which triggers an oscillator when struck. I think I’ll keep these ones just as amplified acoustic instruments as part of the percussion rack I’m putting together.

Anyway here’s what they sound like:

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(using soft rubber mallets to play the 2nd movement of György Ligeti’s “Musica ricercata”)

I haven’t done any audio processing, the recording is straight from the piezos to the desk to the pc. I think I’m going to have some fun with these.

So yeah, the question: what should I call them?