Using a novel way to control audio signals from a plasma, Telmatronics are developing Groovetube - a proto-instrument that can make a wide range of sounds from ordinary fluorescent tubes. Various types of tube produce different sounds, which can be mixed with other audio signals introduced into the plasma drive system, making this a versatile machine for experimental noise-making.

The fluorescent driver can be controlled with external signals or with its own onboard control system, currently in final development. This page will be updated with demos and details of specification/performance as the project continues.


Groovetube machine

Groovetube is evolving as a working prototype machine, with many controls added as functionality is increased. When this process is complete, we will design a more sensible control layout before first machines go into production.

The fluorescent tubes used by this machine are due to be phased out soon, but we are securing adequate supplies for the short term. We are excited by the prospect of developing our own tubes, and intend to start this as soon as possible. Our own tubes will be made to fit these drivers.

Working Spec

The machine uses a nominal system voltage of around 350 VDC to drive a cold cathode discharge inside a 9" T5 fluorescent tube, using RF coils for auxiliary excitation. Power supplied to the tube voltage and excitation systems is regulated by preamp valves, which are well-suited to handling high voltages, and valves are also used for the audio circuit. The telmatron's systems for regulating tube voltage and excitation are controlled by voltage signals coupled in optically for isolation, and the RF system has an additional slide control which allows plasma stability to be altered.
An internal control system enables stand-alone operation, or control is possible by external inputs for two modulation signals and CV/gate. CV controls onboard oscillators that introduce audio signals to the plasma drive, and externally-generated audio can also be fed in. 

Internal control system:
Onboard control can run preset CV sequences and gate patterns, and generates a timing signal for synchronising with other equipment. Two digitally-controlled LFOs are used to create signals for modulating plasma voltage and excitation. This allows good control over frequency and phase relation, which significantly affect the sounds produced. 

Release details

In early 2023 we made Groovetube available for pre-order in complete and kit form as part of a Kickstarter campaign, which ran until March 23rd 2023.

Later this year we will open for further orders. In the meantime, you can register an interest here.

We have promised to post schematics and construction notes - this will happen in in due course when the circuit is finalised and time allows.

This article was updated on July 6, 2023