New Unusual Oscillator

Delton Horn describes several Unusual Oscillator circuits in his 1987 book Oscillators. The Novel Rectangle Generator is one of my favorites and the core of devices going back as far as the Horndog and more recently in the Quad Trzypsy.

The main concept is in duplicating simple circuit elements and connecting them via a recursive feedback network. Stage 1 triggers Stage 2 which triggers Stage 3 which triggers Stage 1. Unequal component values in each stage will result in jerky rhythms and unpredictable behavior. Tapping multiple outputs from different stages is akin to listening to different singers in an infinite canon.

The Grackler explored a similar concept to Horn's NRG, but with a group of four repeated circuit blocks (in this case, quirky voltage controlled oscillators) connected in a loop and with a frequency modulation based relationship between each oscillator. In addition to slight variations in actual component values due to manufacturing tolerances, variations were produced by adjusting the modulation depth between each oscillator and its partner. The oscillators in the Grackler also had a wonderful "freezing" characteristic below a certain voltage threshold which caused them to hold an unpredictable HIGH or LOW state until they were kicked back into action by a rising voltage.

Anyway, there is a lot of juice in this concept and the particular quirks of the repeated circuit element that you use can take on new characteristics when connected via a recursive feedback network.

Above I propose a new type of Unusual Oscillator spiritually related to Horn's Novel Rectangle Generator, but using a different type of repeated circuit element. Here we're using a pitch tracking circuit based on a Phase Locked Loop built with loop filters that have highly slewed response such that they will almost never latch on to a specific frequency.

By selecting different values of timing capacitors (marked with an asterisk) and adjusting the values of resistors and capacitors that make up the loop filter and frequency offset (R1 and R2 on the 4046s), we get a circuit that gives simultaneous unpredictable behaviors from different output taps and which operates over a wide frequency range with only a handful of parts. The values listed in the schematic above are a good starting place, but you can fiddle with any of the component values to get different results.

You can also develop your own Unusual Oscillator circuits by taking some simple circuit element, repeating it and adding some form of feedback. If a loop of two elements does nothing interesting, try three or four or seven or thirteen. Even the least inspiring "my first oscillator" and amplifier circuits can reveal great complexity when connected ass-to-mouth ad nauseam.