the unit has two oscillators made from a 4093 quad two input nand schmitt trigger ic, a 4040 ripple counter and a vactrol doing most of the work. the first oscillator acts as a tempo control, supplying a clock pulse via one of the simple oscillators using a 1uf capacitor. this provides very slow metronome pulses right up to what our ears believe to be a steady tone since its going so fast. a 40106 schmitt trigger could also be used, but i have loads of the 4093 so decided to use them up instead. it was based arround some ideas i gleemed from the nicholas collins book.

the output of this first oscillator feeds into the clock input of the cmos 4040 ripple counter. the counter has 12 outputs but i’ve only utilised 7 that i felt were suitable for this units intended function, and thats to generate crunching, rhythmical patterns and loops for music production at low speeds, or squeals, bleeps and bloops at higher speeds, and some cool ray-gun sounds suitable for 1940′s throw back sci-fi tv shows… or so i’ve told.

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some thoughtless tweaking…

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some more thoughtless tweaking…

these samples were recorded with no effects, just raw audio, and all i was doing was playing with different switches, tempo and tone. scroll down for a few more loops with effects.

each output of the counter is connected to one of 3 switch positions, centre = off, up = on (through a limiting resistor) and down = on (through an led), allowing control of the patterns and loops it creates. from here, the leds and resistors are connected together and feed through a starve pot, and finally into a vactrol. the resistors create a more bleepy reaction to the outputs of the counter. the leds drop the tone a little and produce a steady pulsing sound, while of course providing a visual feedback, but high speed switching diodes such as the 1n914 or 1n4148 could be used as well for the same effect.

the three pots provide tempo control (left), volume (middle) and oscillator two starve/tone control (right). on the left hand side a power switch connects the battery to the pcb, and a 1/4″ mono jack output on the right. the unit runs off of a 9v battery. while it was designed for generating audio, the output could be attached to a vco, vcf or anything else that will accept control voltages. i hooked one up to a filter from my moog and a patched out sound lab minisynth which produced some really great noises, but i’ll need to do that again and get some recordings.

a vactrol is an optocoupler, which contains a light dependent resistor and an led  housed in a sealed unit to prevent light contamination from other sources. the control voltages coming from the 4040 and associated led/restistors and stave pot connect to the positive side of the led in the vactol, the other side goes to ground. the ldr side of the vactorl is used as a pot to control  the resistance of the second oscillator, which creates the sounds we hear. because these oscillators arent voltage controlled, the vactrol provides an excellent interface for pseudo voltage control.

you can easily make you own vactrols but i ended up going with the perkin elmer units for ease, as there is a lot of wiring for the switches involved and i couldnt be arsed making my own after a while. if you make your own, try different ldr’s for different sound/effects. i found the easiest way to make them is to take a bic pen, chop a bit off the case/tube and insert an led and ldr in each end, then a splodge of silicon to seal the ends and hold everything place. be careful not to let the legs of the led and ldr touch and short circuit, then wrap the whole lot in a bit of electrical tape or heat shrink tubing.

the pots are pcb mounted which reduced the amount of wiring meeded and also holds the pcb in place, avoiding the need for mounting it on the chasis. the box used is from hammond enclosures extruded aluminium range, they are sturdy little things, which i’ve used for effects pedals and the vga synth in the past, and can survive a good beating!

there’s a lot of drilling and soldering in these things, but it’s well worth the effort for a box that pumps out nice rhythmical loops and drones.

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loop 1 raw/fx

these are just examples of the types of patterns and loops it produces, there were 3 different switches engaged on each one, first raw audio, then with effects from ableton, simple delay and auto filter, sweeping the frequency of the cutoff, and a little bit of resonance.

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loop 2 raw/fx

given you have 7 switches and 3 positions for each, the combination of patterns equates to 343. i think. correct me if i’m wrong. but either way there is lots of scope for some weird and funky samples and effects to be had from this little box.

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loop 3 raw/fx

the whole thing can easily be set up on a bread board, which is where all of my projects start, and then on strip/vero board, but i sprung for some professionally made pcb’s for this project in the end after testing everything and letting jamie abuse them for several months to see what needed tweaking/fixing. he’s been using this unit for some of his own production work.

how to use it? first, plug in a mono 1/4″ jack to the right hand side of the unit and adjust the knobs, best to start with the volume (middle) down low and the tempo (left) and tone (right) about half way, and switch it on. then set some switches to produce patterns till you find something you like, whilst also adjusting the tone and tempo to your liking.

the 7 switches adjust the patterns. try flicking the switches individually to see how they react. the leds provide a slightly lower tone to the resistors.  when using the far left two switches (q8 and q9), they will change the pattern after a count of 4 or 8 for a period of the same duration and then back again. the other 5 switches produce pulses of varying rhythms. the outputs of the 4040 used are q3, q4, q5, q6, q7, q8 and q9 (from right to left switch positions).

Click to see larger image

alternatives:

• the first oscilator in the circuit could be replaced with a square clock pulse from any where as long as it doesnt exceed 9v.
• try different resistor values or control methods for the pots.
• use the other gates for hard sync control or signal gating.
• make a few different vactrols and see what you like best.
• use ldr’s to control each output.

the leds provide visual feed back, and when adjusting the starve/tone knob, leds will dim and brighten as the 4040 cycles through the outputs selected. diodes could have been used instead and produce the same effect, but who doesnt love a blue flashing led from time to time?

the pcb’s were designed in eagle cad. because i only used two gates from the 4093 ic, the other two gates inputs were tied to ground to prevent any odd behaviour from them. the clock input of the 4040 was tied to ground with a 100k resistor, and 100uf and 0.1uf capacitors were used across the power lines to smooth out any spikes, which is recommended in the data sheets, but is really just good practise when designing anything, especially synths and filters.