Meet the Telmatronics Groovetube Tube Based Prototype Plasma Synthesizer

video uploads by Telmatronics

via Telmatronics Kickstarter

Make crazy sounds with fluorescent tubes, that you can control with a magnet

A project to create a plasma instrument About a year ago, we discovered a lot of fun could be had with a fluorescent tube and a magnet... Lit fluorescent tubes are filled with plasma - a low pressure electrified gas that can make oscillations at audible frequencies. With suitable control over the plasma in the tube, we found this instability could sound amazing... and could also be controlled with a magnet! (It is worth listening to the video with headphones, to hear details of the sound).

Playing with sound created in a glowing tube is tactile, surprising and absorbing, and we decided to develop a new kind of electronic instrument.

We are releasing this first-generation machine for people to try out a new way to make noise. It is a sort of proto-instrument - an experimental machine to be experimented with!

Having machines out in the world will help explore what is possible, as there is a lot of unexplored territory here - we don't have much audio equipment, and have tried a dozen or so tubes. By making these machines available now, we hope to not only fund further development but also let collective experimentation inform its direction.

There are pros and cons to using commercial tubes for this. The sound from different fluorescent tubes can vary considerably, so trying out a new tube is an inexpensive bit of fun. It is currently possible to find various types of suitable (T5, 9"/ 225 mm, 6 W) tubes potentially available, new and old stock. On the downside, these tubes are being phased out in the very near future (about 18 months in the UK), and they will become increasingly scarce as production declines - bad timing to find a new use for them! We will keep testing different tubes however, and secure adequate supplies of some good ones before they disappear. In the longer term our objective is to produce custom tubes, which will require further research and development.

We are offering this first on Kickstarter, as a good way to generate awareness of what we are doing and to generate funds to get the project going properly.

Groovetube Driver

We'll try to tell you all you need to know about this machine here, specification at the bottom.

First, and most importantly:

This is not a conventional synth! Do not expect something you can plug a CV cable into and get a conventional response. Plasma can be unpredictable and is hard to control precisely, and there are many easier and better ways to accurately produce pure tones. This is a controllable tube driver, that can cause plasma to produce grooves and bizarre noises.

Secondly, you may have noticed the machine in our video looked a bit battered, and changed its labels once or twice... this is the working prototype, which has been re-configured and had extra controls added as it evolved. The production units will look broadly similar, but with a more sensible control layout and a smarter case - this is still in development right now, and we will send pictures to backers when we have them. (And if anyone is dismayed, a case like the prototype will also be possible!)

Here are more details about what this is, and what it's like. I was going to do this in a FAQ style but there is a proper one of those, so here are some Questions I Frequently Ask Myself:

How would you actually describe this thing? I'm not completely sure - it is a plasmaphone, and so an electronic instrument. It is also a bit like an acoustic wind instrument in having sound produced by waves in a tube, although they are different kinds of wave. Some of the noises do sound like wind instruments and even rushing air, which is surprising as there is very little gas in the tube.

How does it work? Plasma is excited in the tube using a low-power RF generator, and a high voltage applied to the tube; these are then regulated to control the sound. The magnet works because magnetic fields bend electron paths, making them more efficient in the in the plasma. At locations along the tube this has a different effect on the discharge as a whole, and so the sound.

Is it safe? This is high voltage equipment - similar to a valve amp and as safe as one, but requiring the same degree of respect. This obviously applies to the kits also - DO NOT try to build a kit unless you are competent enough to build a valve amp safely. Compared with the prototype, production units will have an additional layer of hard insulation around the exciting coils (the dark bands around the tube). Regarding the optical output from the tube: fluorescent tubes were not designed to be driven like this, but although the discharge inside will be a bit different from usual this presents no additional hazard. The visible output can be stroboscopic at high modulation, and units will come with a shade for the tube. DO NOT use germicidal UV tubes (pond cleaner etc.) as these can emit harmful UVC radiation. The clear plastic tube guard should stop this, but it still may attack the plastic. Bug zapper or blacklight tubes are not a problem in this respect, though seem quite hard to ignite.

Is it like a theremin? Aside from being able to affect the sound remotely, not very much, no. Theremins work by producing high-frequency EM fields, which get slowed down by a body part to affect the sound, whereas the Groovetube sound is produced directly from plasma oscillations.

Isn't it a bit expensive? For a bit of valve gear made in the UK, no. The valves and transformer are quite expensive components, and the valve circuit is wired point-to-point which takes time to assemble.

Get it made abroad then? This is a new kind of machine that has not been manufactured before. By having initial production take place more locally we aim to make any troubleshooting easier.

So why the valves? Valves are ideal for handling high voltages and generating an RF signal. The fluorescent requires a high voltage transformer in any case, so a bit more glass makes a lot of sense here.

How long does a tube last? We don't really know. I think it will vary from type to type, but I would be surprised if many work well for the advertised 5000 or 10000 hours! The electrodes in these fluorescents are coated filaments, which get 'sputtered' by ions over time - material gets blasted off, causing darkening of the phosphor and changing the discharge characteristic. I have had a new Sylvania tube change its sound over a matter of minutes, but most seem to be much more stable. The Energetic tube in the video has seen a lot of abuse during the development phase (you can see the darkening at the ends) and has been driven for tens of hours, but still sounds fantastic.

And the valves? Same as for a valve amp, many many hours. The prototype still works with some old second-hand valves I have, and I don't anticipate any anomalous loss of performance with time. A replacement set of valves for this machine will cost around £80.

Technical details

The machine drives a cold cathode discharge inside 9" T5 fluorescent tubes, with a nominal system voltage of around 350 VDC,

Excitation uses RF coils.

Control signals are coupled in optically for isolation.

Systems for regulating tube voltage and excitation are controlled by voltage signals which can be individually modulated, and the RF system has an additional slide control.

Onboard control has ranges of preset CV sequences and gate patterns, with two harmonic signals generated by digitally-controlled LFOs for modulation. This allows control over frequency and phase relation, which can significantly affect the sounds produced. This system is run by an arduino board, that also generates a timing signal for synchronising with other equipment. External inputs will allow control by two modulation signals and CV/gate signals, although these will not always produce a standard sort of response!

Mono output is from a valve follower, impedance 68k, signal around 1 V pk-pk. This works fine plugged into my stereo system amplifier or mixer.

I will add to these as I remember things I've forgotten, please ask if you have any queries.

If you live outside of the UK please be aware you may incur import costs/taxes etc.


About us

Tom and Cat share a passion for electronic and experimental music. Cat has supported the initial development and been a pioneer voyager in plasma sound, while Tom has been responsible for concept and engineering. They live with their family in the Northwest of England. Massive thanks to Ed and Max for help with testing the prototype.