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Audiofanzine put the Waldorf Streichfett digital synthesizer to the test. Released earlier this year, the small box is designed to replicate the sound of vintage string machines.
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Thermatron: the flame-controlled synthesizer

Submitted by on April 28, 2010 – 12:50 pm No Comment

It’s fairly well known that a flame can actually conduct electricity. For example, many hot water heaters use this principle – a current is passed through the flame, which allows the the heater to detect if the flame goes out because the connection is broken.

Lorin Parker and Sarah Seelig, who call themselves “Electric Western”, have designed a synthesizer around this idea. The THERMATRON is essentially a voltage controlled oscillator and wave shaper controlled by the action of a flame.

The right mixture of gas, air pressure, high voltage, chemical ions and heat vary the flow of current through a flame. This current feeds into the grid and / or plate of vacuum tubes controlling an Electric Western Phantastron Synthesizer. The right mixture of gas, air pressure, high voltage, chemical ions and heat vary the flow of current through a flame. This current feeds into the grid and / or plate of vacuum tubes controlling an Electric Western Phantastron Synthesizer.

It’s a bit more complicated than sending fire into the input jack of a synth though! How much the flame conducts is dependent on air pressure, chemicals present, voltage and other factors. Ions are also added to help increase the conductance of the flame.

As the flame heats up, it creates more energy in the entire system, with more ions flying around and creating more plasma (a highly energized gas), creating a space much like the space in a vacuum tube. 200+ volts are applied to the top electrode, and a small number of electrons are attracted to the bottom electrode, creating a small current.

Many vacuum tubes behave in a VERY similar way – low current, high impedance, high voltage potentials. Even the concept of “heating” a vacuum tube’s cathode to create free electrons is remarkably similar. Indeed, the flame, in optimal operation is acting like a diode of sorts. This is due to “The Edison Effect” which you’ll have to read about somewhere else.

A chemical coated rod is inserted into the flame, which changes the pitch and modulation of the sound as it deposits new molten ions into the system.

Interestingly, the flame flickers in time with the changes in sound – This is because the changes in voltage make the flame change shape, shrink, and grow.

Check out the video of the Thermatron in action:

The science involved is very interesting (possibly more interesting that the actual sound coming out of it), but it is also dangerous – definitely do not try this at home!

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