S C O T T P E T E R S E N ∞ E L M U C O ∞ S C A C I N T O . C O M

homepage for scott eric petersen, el muco, and all things electronic

Fun with the Wien Bridge Oscillator


Look ma, a (almost) sine tone!

To the fledgling electronics enthusiast who has just enough knowledge of electronic music theory to be dangerous, it makes sense that the simplest tone, the sine tone, should be the simplest/easiest to construct in the analog electronics domain.  Of course, this is not the case.  While geometrically simple to describe, the sine tone is not easily achieved using electronic components.  Most designs found online indicate that the most common method is to “filter” a square wave created by an op-amp through a given set of components placed between the output, the non-inverting input, and the ground.  This is the method employed by the Wien Bridge Oscillator. Read the rest of this entry »

Filed under: DIY, Tutorial / How-to, , , , , , , , , , ,

Make Testing Speakers for Free**

Required Parts:

  • 1-2 8 ohm speakers
  • an enclosure (cardboard box, tea tin, coffee can, etc.)
  • insulation (cotton, an old shirt, the hair you get from your pet when using the Furminator.)
  • wire
  • glue ( any will do, but… I cannot recommend a hot glue gun enough. see below)
  • alligator clips (deluxe version) or just some metal bit that will conduct the signal.

Required Tools:

  • soldering iron (and solder)
  • X-acto knife or other cutting tool (depends on the material of your enclosure.)

Recommended Tools:

  • wire cutters/stripper
  • helping hands
  • hot glue gun (and glue)

As the asterisks in the title imply, and as you know from life, nothing is free. If you don’t have the parts, you will have to acquire them. Read the rest of this entry »

Filed under: Phase 1, , , , , ,

Sparkfun Amplifier Kit (and Power Supply Solution)

Look at the size of that heat sink!

The Sparkfun STA540 amplifier kit is a cool, fun to put together amplifier kit that employs the STA540 amplifier chip at the core of the device.  The chip itself is a 4-channel AB amplifier chip that can be employed in a number of ways depending on the circuit configuration.  The kit is really easy to put together, not because of the included instructions, but because the components are actually labeled on the board.  This really is a foolproof kit and a great introduction for the new audio electronics enthusiast.  The sonic results of the kit are pretty impressive too.  It has a good bang for the buck at 38 watts per channel (2 ch) at 18 V and 4 Ω speakers, and has a low noise floor for an affordable ($30) DIY kit.  Additionally, and as evidenced by the picture above, it has a small form factor.  That is, despite the enormous heat sink.  Holy mackerel!  (Okay, the wide-angle lens distorts it juuuuuuust a little.)
Read the rest of this entry »

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IBeam Laser Show (2011)

It has been almost five months since MuCo performed for the 2nd time at Ibeam and for one reason or another the recording has sadly sat neglected on a hard drive since then.  I finally dug it out, mixed the tracks together (output of kane + scacinto) and here it is for your listening pleasure.

(Just in case you are wondering what the laser-gun sounds are that occur at the beginning and, even more noticeably, during the middle of the recording [11:18 ->], they came from a magical black box that Kane made and I played without knowing how it worked. Hilarity.)

El MuCo @ Ibeam May 28th, 2011

Filed under: El MuCo, , , , , , , , , , , , , , , ,

Electronic Music from “How Things Work” c.1970

On a recent outing to a local bookshop I encountered a 4 volume set of books titled “How Things Work.”  It is a wonderful compendium of knowledge in simple but not simplistic language with really great illustrations.  The four volumes cover everything from knitting to jet engines.  Naturally what caught my eye were all of the electronic devices and processes; everything from how tape recorders, phonographs, and records (LPs) are made and function to broadcast television and electronic music.  I here submit them to you for your enjoyment. The pages are available in two ways, a scanned pdf of the entire section and the individual pages as jpegs.  You can download the pdf from Scribd, and the jpegs you can download by clicking on them to bring up the image page.  Enjoy!

Here is the electronic music section (pg.s 202-214 in volume IV) as jpegs.

I have not researched the origins of the book, but they are obscure.  From a review on Amazon:

It is a 4 volume set, originally published in Germany or Switerzland around 1970. It was translated into English soon thereafter and is now out of print, but you can buy it used on EBay, or Amazon, or ABE Books.com.

A puzzling thing about the English edition of the book is that it does not include the name of the editor or author(s), nor does it include the publication or copyright date. Odd. The only name mentioned is the illustrator, R.J. Segalat.

In this case the reviewer is mistaken.  The illustrations were only “researched by” monsieur Segalat according to the forward of the English edition.  Any comments with information about these volumes are appreciated!

Filed under: Miscellany, Music, Phase 1, , , , ,

Xbee: Information and Resources

The XBee RF radio is certainly not new technology, but it remains a tried-and-true means of communicating with microcontrollers in DIY electronic projects.  For those of you unfamiliar with the XBee, it is an RF radio module that can be attached to a circuit via a breakout-board and used to communicate wirelessly with that circuit, or to send sensor data to another XBee (presumably attached to a computer.)  Working with XBees is not all crackers and cheese, however.  Those familiar with the XBee know it is a device of both promise and sorrow, a ‘veil of tears’ as Allan Schindler would say.   Read the rest of this entry »

Filed under: Tutorial / How-to, , , , , , , , , , , , ,

Analog Ring Modulation Circuit

Above is a video and below are some pictures of a simple ring mod circuit I whipped up last night. The circuit is the classic circuit, and I’m simply running two oscillators from a hex schmidt 6-oscillator IC through the circuit as the carrier and modulator. The frequencies of the hex schmidt are being controlled by a PSR (photosensitive resistor) and an FSR (force sensing resistor) respectively. The video shows fairly well how the PSR reacts to the light. The function of the FSR is a little less clear visually, but you can hear it pretty plainly. I can throw up (!) a schematic of the circuit if anyone is interested, but you should be able to find one by doing a google search.

The project requires a 5V power source (batteries only!) a bread board or project board, some wire (i prefer solid-core) two diodes, two capacitors (0.1uf), 1 133k (or thereabouts) resistor, one PSR, one FSR, one hex schmitt oscillator (mm74c14n) and an audio cable or female 1/8 audio jack to run into a) an amplifier, b) a mixer, or c) your computer.  In this case I have two alligator clips attached to the cut-off and split end of a 1/8 audio cable, the other end of which is running into a mixer and then out to small speakers.

Next on the agenda I think I’m going to build me an ADSR for it. This site has a really great page on ADSRs with diagrams, circuit board patterns, etc.

Filed under: Current Projects, Miscellany, Phase 1, , , , , , , , , ,

Introducing The Little Princess!

What was once the hideous DJ Crappy Tunes (aka DJ Crappy Turntable) has been reborn as the beautiful and talented “The Little Princess!” To see/hear some of the genesis of this beautiful machine, please see our previous post.

Below is the first video of The Little Princess. Here, Kane is taking her for a ride with her lid closed: no peeking!

Here is another video with The Little Princess’s lid open. See all of her wondrous insides? Watch Kane play with them and make her giggle with delight! (SICK!)

Finally, here are some pics of The Little Princess immediately after her reassembly. Enjoy!

Filed under: El MuCo, , , , , , , ,

DJ TOY THING (aka DJ Crappy Turntable)

DJ Crappy Turntable: VIOLATED!

El MuCo has begun work on a number of one-off instruments, one of which is briefly described here.  This fantastic pile of crap was once a DJ toy whats name I have forgotten, but will refer to as the DJ Crappy Turntable or DJCT for short.

This instrument had two “platters” on the top side (not shown) made of ridge plastic and attached to the instrument with screws.  On the underside of the platters were gently sloping ridges which, when the platter was turned, would cause buttons which were inserted in the holes (visible in the lower-right side of the picture in the black part of the case) to be pushed in.  This would close a part of the circuit and cue a short audio clip which would make a squeaky “DJ” scratch noise, or another amusing sound such as a dude yelling “Hit it!” in the style of Bad Dudes.  (dating self here.)

The instrument has a dearth of good bends, but after a few goes we were able to find several points on the board that connected to the amplifier circuit that, when engaged, would give either an ear-piercingly high wail, or a low cosinish-sounding moan.  The below pic shows these two points.

A bend (the only) on the DJ. Note the red clip bridging/touching two resistors

When testing the bend by running the sound into a computer and recording it, we severed the connection to the speaker.  The result was that the bend no longer functioned because the speaker itself supplies a certain amount of resistance.  By replacing it with a 4.7 ohm resistor, the bend was once again functional.

The speaker resistance replaced with 4.7 ohm resistor.

Here is a recording of the bend in action.

Here is a fantastic sonogram of the first 12 seconds of the sound file.  Please note DC has been removed ;)

The first 12 seconds of the above sound recording

This instrument suffers from what a lot of more up-to-date instruments suffer from — a lot of surface-mount resistors, and complex digital  ICs without a lot of analogue leads.  The result is that, more often than not, newer toys end up having one, maybe two good bends.  Usually the built-in sounds are intolerable, and the bends involve tweaking the timing circuit down to the point that the sound is unrecognizably low/slow, or bending something in the amplifying circuit which results in distortion/masking of the original sound.

Neither of these is a particularly worthwhile or rewarding endeavor if the original sound wasn’t worth a damn.  However, sometimes one can find bends that result in original sounds, in other words, not part of the IC programming.  In this particular case we have some potential.  A touch sensor may be employed to give us a little more control than the potentiometer in use (100k).  But the end result will be an instrument with very little sonic flexibility.

Our next project will be to start housing these “one-off” instruments in modular patch-bay style housings where boxes will contain more than one instrument, and all of the connections will be made to a separate control box where we will have touch-sensors, potentiometers, etc.

Filed under: El MuCo, , , , , , , ,

Casing the Casio SA2

There are a lot of sites/posts online with either audio or video of bent Casio SA2s. One site in specific has a lot of great, detailed information on the Casio series, and that is CasperElectronics‘s site.  In fact, his site should be required reading by anyone looking to learn anything about hardware hacking.

That said, it is way more fun to explore an instrument than it is to read about it!  Just doing what’s been done, or just following directions kills what makes HH such a joy — the thrill of the chase!  The key to exploration is knowing how to sail (ahoy, amass those Sprogs n make fer thar swaggy!) and where to sail (say, is that the edge of the world?  forward, ho!!!)

El MuCo prefers to lick-n-stick first, and read second (if at all…)

Here is the SA-2 with the top case off showing how it looks prior to having the case sealed up again.  You will notice that work not described here as already been done.  This is the problem with non-linear pictorial placement.

Here is a close up picture of the part of the circuit where bridging some of the resistors results in pleasing sonic/musical results. In the recording below, I was simply using a 4k resistor on 1 with a quick, light touch.

Click on it to see the 1024×728 version.

Here is a recording made tripping the resistors marked 1 & 2 above.

Here one can see the connections we’ve added in the form of wires soldered onto specific legs of the two integrated circuits.  The white box at the left is the timing crystal.  Note the black wires next to the timing circuit.  These were soldered in place of a resistor which we removed because the wires were easier to “play” as indicated in the “tripping the resistors” comment above.  Unfortunately, it turns out, pulling resistors from circuits and maintaining the overall resistance is not as easy as measuring the resistor and putting in a substitute elsewhere.  As any electrical engineer (and now El MuCo) can tell you, length and thickness of the conductive materials will affect resistance.

Another View

Because we couldn’t fit the pots in the case, and there was already a dearth of space from all the wires, we decided to annex the control interface to another enclosure.  In the below picture you can see the wires from the board running out through holes drilled in the case.

Here is the control module.  The box is a standard Radio Shack project box with three bends, each with its own on/off switch.

We never put the keys (musical keyboard) back in the Casio case as it was deemed superfluous.  One can find images of hacked SA-2s all over the web, many showing bends built-in to the original case.  Our decisions were not purely aesthetic; we had a show in a week, and needed to get this thing wrapped up.  Having said that, the modular approach is appealing for a number of reasons.  We plan on cutting the wires to the module and building in an RCA patch bay.  This way, the two units can be taken apart for transport.

Filed under: El MuCo, , , , , , ,

G O I N G S O N : L O C A L (ISH)

fritz Art of Fritz Horstman
kane Music of Brian Kane
fritz Hartford Phase Shift
fritz Hartford Sound Alliance
Lique Art of Philip Lique
Lique Music of Matt Sargeant
strycharz Art of Heather Strycharz
uncertainty Uncertainty Music Series

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INI new haven

Handmade instruments by Scott Petersen and Brian Kane at Artspace New Haven