Telmatronics are developing Groovetube - a synthesiser that produces sound using a plasma tube, that can be expressively controlled with a magnet.

The machine is configured as a valve pre-amp, with a telmatron plasma tube placed in the current path. The plasma sound produced in the tube has a complex effect - more than simply 'noise in the pipes' as introduced audio signals draw current from, and so affect the plasma instability. The output consists of the interaction between them.

The synth can be controlled with external signals or with its own onboard control system. This page will be updated with demos and details of specification/performance.


Our most recent demo videos show the working prototype in an almost-finished state.
Operating alone:

And with other instruments:

This prototype has had many controls added and removed along the way, a different control layout has now been designed for the first production machines.

The fluorescent tubes used by this machine are due to be phased out soon, so we've secured adequate supplies for the short term. We intend to develop our own tubes for specific sound output - an exciting prospect that will take a little more time. First experiments are now being constructed, watch this space for any news.

Working Spec

A system voltage of around 350 VDC is used to drive a cold cathode discharge inside the tube, and run an RF generator for separate plasma excitation. RF energy is transferred to the plasma with two coils. Power to tube and excitation circuits is regulated by preamp valves, and valves are also used for the main audio circuit. 

The synth is controlled by CV/gate and modulation signals, that can be generated internally for stand-alone operation, or taken from an external source. Externally-generated audio can also be introduced. Onboard control uses a simple 8-step sequencer to 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, allowing good control over frequency and phase, which significantly affect the plasma sound. Control signals are optically coupled into the telmatron systems, with a slide control for varying plasma stability.


In 2024 we intend to produce a batch of 100 instruments.
These will accept 6W T5 fluorescent tubes - we have sufficient stock to supply a selection of 3 types with each machine. An adaptable tube holder means these machines will also be able to take custom tubes once we start to produce them.

We are just starting production, and prices are subject to change. If this happens, the price at time of order will remain valid.

Please email with 'order' in the subject field. We will then contact you with further details, and to arrange payment of £250 deposit required to secure a machine.
These will be allocated on a first-come, first-served basis.

In 2023 we made Groovetube available for pre-order in complete and kit form as part of a Kickstarter campaign, and we are currently focussed on production of this first batch of instruments. Once these have been delivered, we will move to the next orders, which we expect to deliver during the second half of 2024.

Kits will be available for those wishing to build up their own machines, and we intend to make individual components available/post schematics and construction notes when time allows - this will take some time, please be patient.

This article was updated on May 13, 2024