xenoworld.org DIY and geekishness

Chaosc – A noisy ‘synth’

The discovery

When I first started playing guitar, I got my first distortion-pedal: the Digitech Metal Master. And let's face it, it's not all that good. In fact, it's quite terrible.
So when I replaced it with other effect processors and amps throughout the years, it remained in its box in the bottom of my drawer for a long time.

Digitech Metal Master

Digitech Metal Master

A while ago, I wanted to test how my function generator sounded with distortion. So I plugged the Metal Master in the signal path. What came out of the distortion-pedal was unlike anything I had ever heard before; noisy, oscillating hard-driven overtones with a kind of harmonic distortion. Especially when I fed it with the higher frequencies. What I didn't realize at the time was that the internal battery that was powering the Metal Master was almost dead, just barely providing enough voltage. That was the reason the pedal gave out this crazy noise.

Now, I realize now that voltage-starving audio-equipment isn't something new (Eddie Van Halen has been starving his amps with a variac for years), but at the time I made the discovery on my own by sheer accident. Also, this is voltage-starving a digital device, that has far less chance of yielding results than with an analog device.

Instead of having the circuits on my desk with breadboards and crocodile-clips, I wanted to combine them in a 19" enclosure for my rack in my home studio. And... it didn't happen... Until now, 6 years later (!)

The hunger

First, I needed a way to voltage-starve the Metal Master in a controlled fashion. To find the 'sweet spot', I needed a way to adjust the voltage.

LM2596S

LM2596S

Enter the LM2596S adjustable power supply.

My function generator (SparkFun kit) needed 12V DC and since I didn't want to use 2 power supplies for my unit (one 12V and one 9V)
I also fed the LM2596S with 12V DC. The problem being I was then able to provide the Metal Master with more than the recommended 9V DC.

Left with the danger of breaking the Metal Master, I had to find a way to feed it within the range of 0-9V DC.

So after replacing the on-board trim-potentiometer with a regular potentiometer, I added a 10K trim-potentiometer to the circuit. After turning the main potentiometer far right, I was able to adjust the maximum voltage down to 9V with the trim-potentiometer. Mounting them both on a piece of perfboard and wiring them up to the LM2596S, I had something mountable for an enclosure.

 

 

The function

SparkFun Function Generator

The SparkFun function generator got mounted in a 1U 19" enclosure, the housing of an old HP KVM-switch, identical to the enclosure I used on the GSSL-compressor. The potentiometers (amplitude, coarse-frequency, fine-frequency), switches (on/off, sine/triangle, high/low) and LED were mounted through holes in the front, with wires connecting them to the circuit board.

Luckily, the enclosure has a lot of  embossed threaded holes that I could use with spacers for the ciruit boards.

 

 

 

 

The noise

The Metal Master had 4 potentiometers (level, low, high, morph), one on/off-switch, one LED and two output-jacks (mixer, amp) that I soldered out and extended with wires for mounting in the enclosure. I didn't bother breaking out the DC-jack. I also mounted the potentiometer for voltage-starve next to the controls for the Metal Master.

  

 

The Chaosc

After attaching a 19" blank plate to the front of the enclosure and some knobs for the potentiometers, the Chaosc was finished! I may need to engrave the front plate with some descriptions as to what the knobs do, but that's for later...

 

And here's how it sounds: