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.

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:

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.

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.