The Techno-tari 2600 is an analog synthesizer that replicates a basic square wave synthesizer . It is a synth in its most basic form – but with a handful of controls, can provide anything from squelching Techno bass lines to glitchy arpeggios and droning bass notes. The Techno-tari 2600 provides thick analog synth sounds in a rehoused Atari 2600 console, as a nod to all of those computer game sounds from your childhood.
The basis of the Techno-tari 2600 comes from a well-known circuit by Forrest Mims. Mims has introduced many people to the basics of electronics and has done so with his many beginner’s books. Each of these books contain a wealth of information by providing hands-on learning with dozens of circuits to experiment with. One such circuit is based around the 555 timer and is called the Stepped Tone Generator (STG). This circuit has been made with many iterations, perhaps the most well-known of those called the Atari Punk Console. The circuit, and the name Atari Punk Console, intrigued me to experiment with the circuit and after several modifications, the Techno-tari 2600 was born.
NOTE: Before reading further, this block diagram from Music From Outer Space will serve as a glossary/explanation for the details I will describe. MFOS is an excellent resource for Synth DIY-er’s and is highly recommended for those interested.
After experimenting with the Mims’ Stepped Tone Generator, although it is a fun design, I found it sounding a bit thin and a bit limited as you had to press a killswitch or move the knobs around a lot to get the most out of the effect. But the pulse wave generated had a lot of potential as the basis of an analog synth as you had two controls over the pitch, PITCH 1 and PITCH 2. You could detune them, much like having a two oscillator (VCO) synth, to thicken up the sound and they seemed to work intuitively (i.e. the frequency of the stepped output is reduced in smaller increments as you move the PITCH knobs). So by having the VCO at its core, I added a circuit that emulated three more elements of an analog synth; a voltage controlled filter (VCF), a low frequency oscillator (LFO) and a voltage controlled amplifier (VCA).
One limitation of the original design as I commented earlier was the need to constantly move the knobs/switches to make it sound interesting. By adding an LFO, the waveform is modulated at a set rate leaving hands free to control other parameters. The RATE knob is used to control the speed and can give anything to a throb to fast Techno-speed beating to a drone. Setting the control at maximum is like having the original sounds of the STG.
The FILTER knob acts a tone control or VCF. Swept to its minimum, it acts like a high pass filter i.e. all high frequencies above a fixed point are passed through, cutting out the lower frequencies below the threshold. At its maximum, it acts like a low pass filter. This is subtractive synthesis at its most simplest – subtracting frequencies away from the whole (VCO) to provide a synthesised sound.
A FREQ switch allows a shift in octave of the oscilltor so you can go from chirpy, glitchy sounds to rumbling deep drones with one switch. Due to the change in frequency, the PITCH knobs act in a different relationship than before so experimenting here will give you a different low end result. Switch to the left is low frequency, to the right is high frequency.
Finally, I added a bit of a fuzz boost to beef up the filtered pulse wave, The stock sound was thin but by adding this VCA-esque stage, a thick squelchy sound is sent from the Techno-tari straight to the mixer/amplifier. The LEVEL control is the large knob and controls the final output of the signal.
The Techno-tari 2600 operates off 9V DC using a standard 2.5mm negative tip power supply commonly used to power effects pedals. It has an on/off power switch and OUTPUT jack for pluggin into headphones, mixer, amplifier or effects pedals.
So there you have it – the most basic analog synth with controls of each stage ready for pumping beats, squelchy bass lines or glitchy drones. Run it into an effects unit and come up with more sounds, like the ones in the demo below: