Groovetube synth

Groovetube is now virtually a complete instrument. It took a while to get all the signals working properly on a pcb, and to be able to control plasma stability over the operating range. This is important, as the synth works by exploiting the different noise produced around the stability boundary.
The hardware is now complete, and last bits of firmware are being written for full functionality.

We have finalised production costs, and are able to take orders. Availability will be limited at first by stocks of fluorescents, please see below for details.

Overview

The synth is essentially a valve pre-amp with a plasma tube in the current supply line, and a voice oscillator to create tuned input signals. Variable plasma drive gives control over the noise created as current passes through the tube, which in turn modifies the input signal. The strength of input signal varies the relative plasma noise element in the output sound. Audio output is coupled directly from one end of the tube - there is no 'dry' or pass-through component.

Two input channels are mixed down before being sent to the tube system. One of these is reserved for the tone generator, the other for audio line-in. Controls for input, plasma tube and output are grouped on the interface:

The plasma noise is sensitive to stabilising RF energy applied to the tube, controlled with the slider. It is also sensitive to magnetic fields, and a strong magnet can significantly affect the sound.

Demos

We now have a final-spec machine built up, and will make some comprehensive demos as soon as possible. So far we have recorded a few clips testing the line-in, and one showing oscilloscope traces of the output signal.
Versions of these are available with WAV audio for download, but at present the recording quality is limited. Please bear with us, a better set-up is on the way...

Plasma fluctuations can make some pretty crazy waveforms, like alternating long/short periods and repeating irregular patterns. In the clip below, tube drive is varied with each note, and you can see different types of waveform interacting with the input tones.
This shows some first testing of an auto-tuning system, where the machine first listens to the tube output to learn how to drive it in tune with the applied input tone.
Plasma does not have a linear response to drive conditions, so the system doesn't always produce exactly the same result.

high-quality audio version 20MB

The next clips show line-in tests - in some the synth is running a Fusion brand fluorescent, in others a prototype neon tube. Fluorescents generally tend to add higher-frequency noise, and can produce a very brassy sound. The neon tube is not quite suited to this machine, it really needs more voltage to produce much plasma noise. Run like this it adds warm distortion and definition to the sound, which is encouraging for the next versions.

We have not tested many audio sources yet, but got good results with first sending a signal from the radio or drum machine through a Wingie2 resonator. This boosts certain frequencies of the input, making a compressed/saturated signal that the plasma responds well to - though the output level can vary significantly as input frequencies change.

Three clips showing sounds from live radio put through the resonator, and mixed with tones from the onboard synth oscillator.
high-quality audio version 57MB

The resonator is initially distorting the radio signal, before the synth changes the sound again. In the next clips you can hear first the line-in signal and then the synth output, to show what the resonator is doing and what the synth is.

high-quality audio version 33MB

Two more clips, with the synth running in sync with a drum machine. The hi-hats signal is sent to the synth line-in via the Wingie, with a short decay time on the first clip and long on the second.

high-quality audio version 55MB

Older clips of our previous machine are organised into two playlists on Youtube.
This one has a series of clips showing the machine operating alone, and this one has clips of the synth being tested with drum machine and audio from live radio.

Tubes

The fluorescent tubes used to develop this machine have been a great resource, but are being discontinued and will soon become unavailable. We have some supplies of these for the short term, after that we will be making our own tubes.

Fluorescents we've tried have been really variable. Common problems have been noise that can't be stabilised, and inconsistent operating range - these seem likely to be due to the electrode thermionic coating, and possibly distribution of mercury in the tube. Many tubes seem to settle in after a few hours' operation and become more stable, and a small magnet clipped to the tube by the anode generally stabilises excessive noise. The few tubes we've run over longer timescales, like 100+ hours, have become quieter. We don't yet have a clear idea of the overall lifetime for fluorescents in this machine.
We won't need to use heated electrodes or mercury in our tubes, so should be able to avoid problems caused by these. Electrode shape is likely to be important, we will start to find out soon.

Ordering

Cost
The full UK price is £2,200 - this is subject to any extra delivery charges/tariffs etc. for other destinations.

The price includes:

• One Groovetube instrument in aluminium travel case
• One set of JJ valves
• Three fluorescent tubes- tested for good/different sound
• Delivery

We intend to also supply a custom tube as/when available. If you are interested in one of these instruments, it is worth buying a selection of 6W T5 fluorescents now, before they disappear.

The travel case, synth casing, pcb and transformer are all made in the UK, and the instruments will be assembled here too.

Availability and schedule
In 2023 Groovetube was made available for pre-order in a Kickstarter campaign.
We are now finally building up these first instruments, and our first priority is delivery to some very patient musicians. This is a new machine, and we're continuing to experience snags with production - please be patient, we'll keep solving the problems!

We expect to be able to focus on production by the end of summer 2025.
Availability will be limited at first by the number of tubes that test good from our stock of fluorescents. We can only offer tubes we know to perform well, which right now is enough for a few dozen instruments. We have more tubes to test, and should be able to extend this in the near future - we'll keep posting updates on this, and on progress with our own tubes.

Once a production run can start, the schedule will be largely determined by lead times on components, as the assembly time for small numbers is quite short. The wait from  that point is likely to be a couple of months, so the earliest we'll be able to deliver production machines will be towards the end of 2025.

Ordering
To order a machine, or to ask for updated availability, please enter your email here:

Email: Submit

All contact details will be kept confidential. Alternatively, you can drop us a line at telmatronics@gmail.com, and we will send you further details. Once we're ready to start a run, we'll be able to give you an estimated delivery schedule.

We're still hoping to make kits available for those wishing to build up their own machines, as well as individual components/schematics and construction notes when time allows - this is going to take a little more time, sorry for the wait. A basic schematic of the main circuit can be found here.

Specification

Transformer	Can be supplied for any mains input. Standard model is configured for 110/120/220/230/240 VAC  - please contact us if you require an alternative
System voltages	Valve circuit B+ : 370 VDC Control signals: 12 VDC   Valve heaters: 6.3 VAC
Valves	ECC82 x 1, ECC81 x 1, ECC83 x 2
Tube	6 W T5
Control signals	CV/gate -  internal/external 0-5V 2 x LFO -  internal/external 5V p-p Sync in/out - 48/1,2,24,48 ppb 5V
Audio	Line in, line out, headphones
System control	Arduino Due

RF is delivered to the plasma using two coils. The tube can easily be changed, with  interlocks incorporated in the housing.

Analogue audio path - the signal is routed from the tube anode to tone/EQ stages in the valve circuit, then through volume compensation and gate at lower voltage before being prepared for outputs.

The variable-depth gate can be applied to the synth voice signal before the tube and/or audio output.

Tempo is controlled by the synth or an external signal, with sync signal output for other equipment. Sync in rate is 48 ppb, sync out can be set to 48/24/2/1 ppb.

Onboard control uses a simple 8-step sequencer to run programmable CV sequences and gate patterns.

The twin LFOs are digitally-controlled for good control over frequency and phase. The analogue signals they produce can be applied to modulate tube voltage and plasma stability, and also to the gate signal.

A powerful Arduino Due board runs the machine, and plugs onto the accessible side of the pcb for easy removal. Using Arduino means we can easily send out code updates, and you can also write your own.