Old School CMOS Overdrive - Cloning the Original EHX Hot Tubes

The 1970s was a time of rapid change and development in the electronics industry. Transistors became increasingly common, and the technology to fabricate them saw revolutionary jumps in density and fabrication. Complementary metal–oxide–semiconductor (CMOS) technologies became increasingly common, and were first applied to guitar fuzz effect pedals to emulate a "tube sound" in 1977. In 1978, Electro-harmonix released their own CMOS-based overdrive pedal, the Hot Tubes. It was only produced in its original form from 1978 to 1981 when EHX ran into financial issues. The pedal was eventually re-released as a "nano" series pedal in 2013 and in a dual pedal with the Crayon as the "Hot Wax" later. These are still in production and only run about $80, so while you can save a couple of bucks building your own, it's not one I'm going to produce in any volume!

AionFX has released the pedal as the Hexeract. It's a really easy build with no exotic components - just make sure you socket your ICs. The parts count is fairly low (not as low as the Way Huge Red Llama), but they do both use a CD4049UBE CMOS hex inverting buffer.

Just like the original, the Aion clone has four main controls. Volume is just a normal output while Drive controls the gain of the circuit. Tone is very much like a Big Muff treble/bass control, but this can be turned off with the bypass giving a more distorted tone.

Rather than making an homage to the original enclosure for my build, I went with something more original, and a little "Steampunk" in theme. This is really a fun basic pedal, and the sound is decent. It's just been eclipsed by more capable pedals in the intervening years. I'm certain I'll find a few songs where it can shine, but it likely won't spend nearly as much time on my board as some of my other drive and distortion pedals.