More Mura Filter

Latest version of the Mura Filter includes LFO. Have not built this design yet.  Increased the cap from 10p to 2n2, I'll try this when I get home and see if it works.

VSF Video Demos

Here are a couple demonstrations of my new filter design the VSF.



Got the transistors working now.  Changed the resistors to 10k and switched to 3904s.

VSF

Finished building the VSF (described below) last night.  I had to disable the transistors since they seemed to be on continuously.  Very nice distorted complex tone colors out of this thing.  I need to change the pots to 100k from current 1M for VCF and 500k for Q.  The Mura I need to change from 100k to 1M.  Go figure. I will try to get an example of the sound up here soon.  I may try to change the transistors so I can get some control voltage response.

Mura Filter

From the Japanese term for the waste of uneveness this filter will create an uneven distortion of the resonance structure both from the transistor and from the diode in the feedback path.  Connections are described in the picture.  Values can be changed somewhat to match standard values.  RS is a rail splitter.  Saving the other side for an LFO to modulate the Fco.  Have not built this yet but it looks pretty cool in the simulator.

Falstad circuit simulator code:


$ 1 5.0E-6 0.9891409633455756 50 5.0 50
r 336 320 272 320 0 4700000.0
c 336 224 336 192 0 1.0E-9 0.00268564673175871
c 432 224 432 192 0 1.0E-9 -1.876367065692067
r 272 320 272 368 0 47000.0
c 272 320 224 320 0 1.0000000000000001E-7 -2.4144869775373956
174 336 192 432 176 0 100000.0 0.9059 Q 100k
a 336 336 432 336 0 15.0 -15.0 1000000.0
w 336 224 336 240 0
w 336 288 336 320 0
w 432 224 432 240 0
w 432 288 432 336 0
g 336 352 336 368 0
g 272 368 272 384 0
O 432 336 432 368 0
174 336 192 240 176 0 100000.0 0.9257000000000001 Fco 100k
g 240 192 240 208 0
w 288 176 336 192 0
R 224 320 192 320 0 2 100.0 5.0 0.0 0.0 0.5
r 336 288 384 288 0 2000000.0
r 384 288 432 288 0 2000000.0
g 384 240 384 224 0
c 384 288 384 240 0 1.0E-11 -0.939194425306891
w 384 176 336 192 0
w 432 240 432 288 0
w 336 240 336 288 0
w 336 160 336 192 0
w 448 288 432 288 0
174 336 160 432 160 0 1000000.0 0.005 Resistance
d 464 160 464 192 1 0.805904783
w 384 144 336 160 0
w 432 160 464 160 0
w 464 192 464 288 0
w 464 288 448 288 0
t 288 128 288 160 0 1 0.45948822583066745 0.4568213771495246 100.0
w 272 160 240 160 0
w 240 160 240 192 0
w 304 160 336 192 0
R 288 96 288 64 0 1 40.0 3.0 2.0 0.0 0.5
174 288 96 304 128 0 1000000.0 0.10400000000000001 Resistance
w 304 112 288 96 0
o 13 4 0 34 20.0 9.765625E-5 0 -1

Note the resonance wave form has a slight sawtooth edge as well as only oscillating on the positive cycle of the square wave.

Very Strange Filter 2

I decided to put this into a case.  I get these boxes at Office Max for about $1.50.  They drill out pretty easily with the Dremel dry wall attachment.  Have all the hardware attached at this point but still need to add the wires.

The top of the box.

This shows the circuit board in the box.  No wires attached yet but all of the components are in place.  This is basically a three part filter.  Probably a bit silly of me to make this without breadboarding it first since I don't really know what it will sound like.

Mini Modular NAND

I have been thinking about the NAND synth and giving it some additional capabilities.  This is my plan for a mini modular based on the 4093 NAND.  Each of the four NAND gates would be made into a separate oscillator.  Each oscillator would have three switches three knobs/pots and three jacks.

Switch 1 On/Gate: Determines if it is on all the time or if it can be controlled by the gate input.
Switch 2 Square/Saw: Switches a capacitor on the Cv input (I need to add this cap to the circuit shown above.)
Switch 3 VCO/LFO: Switches the feed back to a larger capacitor to make it into an LFO.
Knob 1 Pitch
Knob 2 Volume
Knob 3 Modulation amount (pitch)
Jack 1 Gate input
Jack 2 Cv Input
Jack 3 Output

This is the basic schematic for this.  Assume the gate starts in state Hi Lo then the 1n cap charges until it goes Hi at which point the output goes Lo.  The rate of charge and discharge is controlled by the pitch pot or by the transistor depending on the base current.  The LED monitors the output and turns on or off based on the output.  The LFO switches in a larger capacitor so it takes longer to charge.  The wave shape applies a low pass to the input signal.  I may have made some mistakes in this drawing but this is basically how it works.

This basic structure is repeated four times.

Next comes the filter which I described in a previous blog.  This consists of three simple resonant low pass filters and a clipping op amp differentiator.

This one does not have the voltage control transistor in it yet so I am still working on that.  It also shows a QF connection on filter 2 which should be bypassed.  The way this filter works is to have both a resonant low pass (with assymetry switch) and a low pass (Q turned all the way down).  Then subtract the two signals and clip them with the op amp.  This creates a complex waveform (supposedly).  Finally feed the result out through the final filter with resonance.  Need to add an additional input for external signals as well as transistors so I can modulate the cut off frequency.  The filter will from the base of the module.

RS is a rail splitter.

Very Bizarre Filter Revisited

A while ago I came up with a design for a very bizarre filter which attempted combine a fuzz distortion with resonant low pass filter.  Unfortunately the prototype did not pan out.  This is a second attempt at a bizarre filter.  The idea is not to create a certain type of filter but to deliberately introduce distortion into a filter. 

This design is based on the new filter Ray Wilson is using on his Noise Toaster.  The Noise Toaster is an excellent sounding box which gives you a lot of options in a small space.  I was looking for a simple filter design so that I could try out some experiments without using a whole pile of chips.  The advantage of this filter is that it uses only one op amp.  I had been experimenting with Ray's Weird Sound Generator filter since it is very simple.  This new filter is an improvement over the WSG filter.

The first modification I decided to try was putting in some diodes.  I found that putting a diode and a potentiometer that could be switched on and off in the resonance section allowed for a lopsided resonance which should give some unique character to the sound.

The second modification I wanted to do was to subtract a low pass signal from the resonant low pass signal. That should result in just the resonance from the signal.  Next I wanted to add some hard edges to the signal so I passed it through the an op amp at high gain.  Finally I added another resonant filter at the end to reintroduce resonance on the newly created peaks.  Leaving in all of the controls gives nine different controls for messing with resonance and distortion.

The left trace shows Ray's original filter, the next trace shows the diode modified filter, the next trace shows the clipped resonance signal and the next image shows the re-filtered signal.

I have not built this device yet, I will have to wait to see if it works out.  If I build it I will post a video.  I am hoping to add a filter to a NAND synth so I may use this one.

Heavily Modified APC

This is a heavily modified Atari Punk Console.  Modifications include pitch and mod Cv inputs, resonant low pass filter from the Ray Wilson's Weird Sound Generator, dual low frequency oscillator with cross feedback, selector knob for up to six different capacitor pairs ranging from control frequencies to high pitched oscillator frequencies.

 The circuit for this is on the bottom right:

Thing 2 vs. Steam Drone

In this video I do an improvisation using my Thing 2 NAND/APC/Noise drone box and Steam Drone box.

The Steam Drone is on the left.  The system combines a NAND synth with a resonant low pass filter based on the LM13700 OTA.  The LEDs use two transistors and capacitors to do flashing lights (yellow and red). The knobs control the frequency of the three NAND oscillators as well as the level of audio sent to the filter.  It turns out the filter performance depends somewhat on the input level.  the next set of knobs include Q, filter cut-off, and output volume.  The knob on the far left is a potentiometer that the input voltage passes through.  When this is all the way to the right it passes the voltage unaltered.  As you move it to the left the input current has to pass through more and more resistance essentially starving the circuit of voltage.  Starve is one of my favorite effects because the circuits get into a mode where they don't behave like they are supposed to, before they shut down completely.  Three of the switches control are used to link the NAND oscillators directly to the output, the other switch turns on the power.

The box on the right is the Thing 2 system.  This is a board I made by combining the following circuits: NAND synth, Atari Punk Console, low pass filter, zener diode noise source, blinking light circuit.  I had a bunch of layouts drawn up so I decided to combine all of these on a single board.  The noise part of the circuit was not making any noise so I kept increasing the resistor value over the op amp to increase the gain but it still would not make noise for me.  I noticed however that the whole circuit was producing noise so I settled for that.  This box has additional inputs for the control voltage of the 556 which basically controls mod and pitch.  I also added an input for the filter to process an external signal since the noise wasn't working.

Something interesting occurs on the Thing 2 when you starve the circuit.  The noise starts to become enhanced and the LEDs start having a big impact on the sound.  I was originally disappointed with the flashing light part of the circuit because the flashing of the lights is not related to the sound the device makes.  As you starve the circuit though, each time the lights flash they make a sound.  So I ended up really liking this circuit.  It was sort of a whim to combine all of these circuits on one board but I like the results a lot.  I ended up with two other indicator LEDs, yellow and green, in addition to the flashing ones, blue and red.

I had photo cube from Michael's which was big enough to hold the circuits and the knobs and I had used a photo cube for the Thing 1 device.  I came up with the idea to cut pieces of Fresnel lens and mount them on the inside surface of the photocube.  This gives a really cool effect when the lights are out.

Hadronistics

Hadronistics involves the study and application of Hadristors; gravitational devices which which play an essential role in FTL (Faster Than Light) transportation.

Took this one down.

This piece was done by improvising four different long sounds using home made boxes including the Thing 2 device depicted in the image.  The Thing 2 device combines an Atari Punk Console, a NAND Synth, an Odd Filter and a noise source in a single box with four LEDs, two of which are blinking.  The walls of the box are covered with fresnel lenses to give the impression of something which look larger on the inside than it does on the outside (TARDiS).  Other instruments used are an APC expanded with a capacitor array and odd filter used as input to a Bass++ drum trigger for rhythm patterns.

The Thing 1 noise source, NAND Synth 1 and 2 with VCF LPF 1, some signals were processed through a Motif with chorus, reverb, phasing and delay.  The entire sound was processed in Reaper with Apple reverb and Voxengo Elephant for compression.

Steam Punk Drone/Noise Box

I found this box at a thrift shop a while ago and was trying to come up with a circuit to put in it.  I finally decided on a circuit made from a NAND synth combined with resonant low pass filter.  The controls are as follows:

Top row (left to right) Power on, NAND Osc 1 to output, NAND Osc 2 to output, NAND Osc 3 to output

Middle row (L to R): Starve (10 kOhm Pot on supply V), Q, Fco, Output volume

Bottom row (L to R): NAND1 Fqc, NAND2 Fqc, NAND3 Fqc, NAND input level to filter.

Back (not shown) Ext. Audio Input, Fco Cv input, Output.

Note: Below the glass plate are a couple of blinking diodes.

The control voltage mix op amp is to the left.  It turns out this section did not function because apparently I forgot to tie some stuff to ground and -V.  The NAND gate chip is on the right.  In the middle is the VCF based on LM13700.  This is the filter schematic.  Note this has an error the transistors on the right need to be grounded.  I think there is another error too.  (The NAND synth section is not shown)  The TL972 I am was using did not seem to work in this application.  I am replacing it with a TL082 in future versions.  Not quite sure why.

Updated circuit diagram and PCB layout.  IC pin spacing should be .1".

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.

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.