Salen-Key VCF

This is a voltage controlled low pass filter with three control voltage inputs and three audio inputs.  Designed for 9V but could be higher.  This design has not been tested so use at your own risk.

Chaotic Circuits

Ian Fritz has a number of chaotic circuits on his page that look really interesting.  I thought I would start with one of the simpler ones.  This is my drawing of the Driven Damped Well chaotic oscillator.  Unfortunately this does not seem to make any sound when I power it on so I need to trouble shoot it.

Update: I did some trouble shooting but it still does not behave as expected. (chaotically) it seems to be passing the original sound to the output.  I am monitoring the NL output so I think I will switch over to the X output.

Update 2: I did more trouble shooting and switched the output to X and now it does indeed behave chaotically although in a not very usable fashion at the moment.  One thing I love about chaotic systems is that they depend on prior initial conditions.  So as you turn the knobs the circuit may not be making any sound, then you pass a point and here a blip, as you tweak around the blip you gradually bring it into oscillation.  Suddenly the oscillation goes away and you get silence again.

I have been feeding the output of an Atari Punk Console in to drive this circuit.  At some settings it has been making some overtones and clicks but they are difficult to find.

Current DIY Projects

 These are some pictures of some current DIY synthesizer projects.  This first one is a 10 step sequencer with a 555 clock.  I used different colored LEDs for each step (not sure if this will mess up functionality yet).

The next one is my DACPOD.  This will be mounted in a case and combines a simple resonant VCF with an Atari Punk Console and my blinking light circuit to give it two flashing LEDs.

 This circuit is supposedly a snare drum but it needs a couple of capacitors and a transistor yet.

This is a Rossler Attractor chaotic oscillator circuit.  Should have put some caps on the outputs for this one.

This circuit combines (left to right) a control voltage mixer, a voltage controlled resonant low pass filter, and a NANDsynth oscillator as well as blinking LEDs along the top.  This circuit ended up as my Steam Drone box.

MFOS Alien Screamer

Ray Wilson has come out with a new circuit the MFOS Alien Screamer:

I really like the sound of this thing and possibly more importantly I like how such a complex sound can be generated by such a simple circuit.  Ray has done a great job of extracting the most functionality out of the fewest components here.  The only thing missing is an appropriate filter to go with it.  I have been working with a couple of VCFs including Ray's Odd Filter from the Weird Sound Generator but I think for this one a LM13700 filter is more appropriate.

Atari Punk Console

This is my layout for my Atari Punk Console.  This is about as compact as you can probably make this device without going to surface mount.  The + and - go to a switch to the battery.  The P+ supplies the positive voltage to the two pots (right side), the PP goes to the wiper of the Pitch Pot, the PM goes to the wiper of the Mod Pot, CvR provides a voltage to the two control voltage RTS 1/4 jacks and should connect to the ring of both jacks.  This will allow you to use an expression pedal to sweep pitch or mod.  Note the resistor presents too much current from flowing if you short out the connection.  The CvP goes to the tip of the pitch control voltage quarter inch, and the CvM goes to the tip of the mod control voltage quarter inch jack.  The output goes to the tip of the 1/4 right of an audio pot 10k-100k.  The wiper goes to the tip of quarter inch jack.  The sleeve of the jacks should all be connected together and grounded.

This design makes use of both modulation connections on the 556 chip so you can modulate pitch and wave shape.

This setup has the following additional components:

2 stereo 1/4 inch jacks for control voltage or expression pedal input
1 mono 1/4 inch jack for output
2 500k - 1M linear taper pots (either work) for pitch and wave form modulation
1 10k-100k audio taper pot (either should work) for volume
1 SPST toggle switch for on/off
1 battery clip or 9V supply connecter (or both)
1 case of some type, a lot of options here but I like the "Really Useful Box" series from Office Depot because they are easy to drill holes in.

Here is a video demonstration of this device:

You can use this to make a PCB.  You will have to scale to the correct size.  The spacing between the pins on the chip should be 0.1 inch.  The output will be the contact on the far right.

Amplifier Demo

This is my current harmonica rig.  I use a Fender Blues Junior amp with a Shure Green Bullet mic.  I also sometimes use an Audix Fireball microphone which basically duplicates an SM58 but does have a volume knob.

The reverb tank went out on this amp so I replaced with a Ruby tank which has a much longer reverb decay time that is supposed to be useful for a "Surf Guitar" sound.  For blues I keep it dialed way down to improve articulation.  For a slower ballad or acoustic I sometimes turn it up a bit.  It was very simple to swap out the tanks.  I was considering adding both tanks with a switch to go between the two.

I have both a 520D and a 520DX.  I recorded some videos comparing these two mics.  The recording was done using an iPad 2 including the volume so I may have been able to capture better tone with a different recording set up.  This first video was done using the 520DX microphone with built in volume knob.


The following video clip demonstrates the 520D green bullet mic from the late 80's early 90's.  The end of this video includes a couple of ambient pieces done with long delay.



Blog out,
Plasma Portal
Hans Mikelson

Circuits

I have been working on some circuits lately.  I am particularly interested in noise generators or chaotic oscillators.  I like to find something right on the boundary between pure tone and noise.  Some of the circuits I have found are the Lorenz system, reverse bias diode based noise, the Rossler attractor and the TMPP chaotic oscillator (my favorite so far).

To make a circuit takes several steps.  First I try to simulate the circuit using the Falstad circuit simulator:  http://www.falstad.com/circuit/ .  After that I use a bread board to construct the circuit:

After demonstrating the circuit works I do a breadboard layout using ExpressPCB.  I then photo and etch the circuit board, drill the holes and solder the components into place.  I try to find a nice looking case to use for the circuit.  In my search for interesting circuits I found a number of web sites.  Music from Outer Space http://www.musicfromouterspace.com/ has a host of unusual noise makers.  In particular the Weird Sound Generator and the Noise Cornucopia are interesting to me.  I currently have parts on order for the Weird Sound Generator.  The Noise Cornucopia has several interesting types of noise beyond standard white noise including filtered and grainy noise.

My biggest issue with circuits is that usually you have to supply them with at least +/- 9V which requires two 9 V batteries.  That's a lot of voltage for a simple noise box so I usually attempt to rework the circuit to 9V but if I need to I can move up to +/- 9V.  Since I'm not interested in doing power supplies right now, I try to stick with battery power.  Op amps require both a positive and negative voltage and a ground located between them so if I put a couple of caps in series between +9 and 0 on the battery I should get a ground in between them.  I usually put some high resistance resistors in series too, though I'm not sure that is necessary.

I had been searching the web for a while for chaotic oscillators and found the Lorenz system: http://ccreweb.org/documents/physics/chaos/LorenzCircuit3.html which uses the AD633.  The Analog Devices chip enables you to multiply two voltages together as analog signals rather than converting to digital which is an interesting trick.  The AD633 is a bit pricey ($10) and Mouser doesn't stock them though Digikey does.  I found a Ring Modulator that uses this chip which should be quite cool, the WARP 633: http://m.bareille.free.fr/modular1/warp633/warp633.htm

So I was surprised to find the Rossler Attractor on the Falstad circuit simulator: Go to Circuits->Op Amps->Oscillators->Rossler Circuit.d

I built this circuit and replaced some of the resistors with potentiometers and made a video of me playing with the knobs.  The output is not that interesting by itself so I added a delay and phaser to the sound:



After searching the net a bit longer I found "A simple chaotic oscillator for educational purposes" by Tamasevicius et. al.  http://www.df.uba.ar/users/sgil/physics_paper_doc/papers_phys/e&m/A%20simple%20chaotic.pdf

The first thing I did was to load the circuit into the simulator.  This shows some classic chaotic behavior on the scope:

The import code for the Falstad simulator is:

$ 1 5.0E-6 0.30802168489180315 50 5.0 50

a 240 224 352 224 0 15.0 -15.0 1000000.0

d 416 224 352 224 1 0.805904783

r 208 240 208 304 0 495.0

l 304 304 352 304 0 0.1 -4.0766317387341106E-4

c 304 304 256 304 0 1.0E-7 -0.08352313181090625

c 352 224 352 272 0 1.5000000000000002E-8 -0.6182734965994132

w 320 144 352 144 0

w 352 144 352 224 0

w 240 208 240 144 0

w 240 144 256 144 0

w 416 192 416 224 0

w 352 272 352 304 0

w 176 240 176 208 0

g 176 304 176 320 0

g 208 304 208 320 0

w 240 304 240 240 0

w 256 304 240 304 0

w 208 240 240 240 0

w 176 208 240 208 0

R 480 192 512 192 0 0 40.0 20.0 0.0 0.0 0.5

r 176 240 176 304 0 10000.0

r 256 144 320 144 0 10000.0

r 416 192 480 192 0 20000.0

w 352 304 416 304 0

w 416 304 416 224 0

O 352 304 352 336 1

o 25 8 0 34 5.0 9.765625E-5 0 -1

Next I built the circuit but I needed to make some changes.  I wanted to use +/- 9V, 200 mH inductor, 500 ohm resistor, 9 V input, potentiometers and a few other changes.  The first attempt seemed to work OK with some real chaotic regions that transitioned from tone to noise.  I would like to modify this to get more range in the chaotic regions.  I think need to get some different value potentiometers to implement this.

That's as far as I have so far.

Blog out,

Plasma Portal