This repository contains the Crystal Palace plugin for VCV Rack. If you like to create weird soundscapes, drifting ambient music, or put your electronica in a blender, you have come to the right place.
The Crystal Palace plugin is free, closed-source, and released under license. VCV Rack is written by Andrew Belt; this plugin uses the VCV Rack API and is offered in compliance with Andrew’s license. The Crystal Palace plugin for VCV Rack was written by David Peterson.
Compiled releases of Crystal Palace are available from the Releases page and from the VCV Rack Plugins page.
The Crystal Palace for which this VCV plugin is named was invented by BBC Radiophonic Workshop engineer Dave Young in 1967-8. The Crystal Palace consists of sixteen input jacks connected so that the received signal is shared by the higher-numbered jacks when they are unoccupied. For example, if inputs are connected to jacks 1 and 9, unconnected channels 2 through 8 receive the jack 1 signal, and unconnected jacks 10 through 16 receive the jack 9 signal. The sixteen input channels are connected to non-rotating input vanes arranged in a circle within a multiplexer drum. A re-purposed variable-speed dictation machine motor rotates a capacitance vane around the circle of input vanes without touching them, forming a smooth capacitive fader. The capacitive vane is connected to the high-impedance input of a field-effect transistor (FET) amplifier using the gold nib of a Conway-Stewart fountain pen. The amplified signal is connected to four output jacks. The device is housed in a hand-made Perspex box, which gives it its name. The Crystal Palace was used by Brian Hodgson on his soundtrack for “The Krotons” episodes of Doctor Who in 1968, as well as “Music of the Brisbane School” for Philip Saville’s The Machine Stops.
The Perspex module is inspired by Dave Young’s Crystal Palace for VCV Rack. While it is essentially a sixteen-channel mixer, it can also be used to create a custom sound source or a complex low frequency oscillator (LFO). Perspex extends the original Crystal Palace device with clock, reset, and control voltage (CV) inputs useful in the Eurorack environment.
Perspex accepts up to sixteen channels of inputs. The input signals are cross-faded as Perspex’s motor rotates the capacitance vane past each of the stationary input vanes. Each channel fades out as the next channel fades in, with an equal-power cross-fade.
Perspex is a fairly large module and is not skiff-friendly. Perspex is 34 HP wide and, due to the motor and multiplexer drum, is nearly 140 mm deep.
The Perspex module accepts up to sixteen inputs through the sixteen numbered jacks on the left side of its panel. Each input jack is wired to the next, higher-numbered input jack (normaled). For example, the signal on channel 1 will also be present on channel 2 if jack 2 is not connected, as well as on channel 3 if both jack 2 and jack 3 are not connected, and so on around the circle. If jack 1 is not connected channel 1 will contain silence and will pass the silent signal to higher-numbered channels. The signal received through Jack 16 is not connected to channel 1. Signals input or passed around the circle to channel 16 will not be passed to channel 1.
A clock signal can be connected to the CLOCK input jack. When the CLOCK jack is connected Perspex advances the capacitance vane by one revolution for each pulse received. It is very likely that you will want to send every fourth or sixteenth pulse to Perspex using a clock divider. When the CLOCK input jack is connected Perspex ignores the CV jack and the SPEED knob.
A low frequency oscillator (LFO) can be connected to the CLOCK input jack. The LFO signal causes Perspex to advance the capacitance vane by one revolution per cycle of the LFO (sync mode).
When Perspex receives a pulse on the RESET input jack, the position of the capacitance vane is instantly moved to channel 1 (the top of the circle on the panel). Channel 1 then fades as the capacitance vane moves past it. When a reset occurs the rotation of the capacitance vane is disturbed, likely resulting in an audible interruption of the output signal.
When Perspex receives a control voltage (CV) signal through the CV input jack, the value is added to the speed set on the SPEED knob. When a positive signal is received the speed of rotation is increased; when a negative signal is received, the speed is decreased. A sufficiently low combination of CV input and the SPEED knob will halt the motor. The motor will never spin backwards due to limitations of its gearing. When the CLOCK input jack is connected, the CV input is ignored (sync mode).
The SPEED knob controls the speed of Perspex’s motor. The left side of the SPEED knob’s range is slower. The right side of the SPEED knob’s range is faster. The value set on the SPEED knob is combined with the value received from the CV input jack. When the CLOCK input jack is connected, the SPEED knob is ignored (sync mode).
The outer circle of LED lights on Perspex’s panel are its NORMAL LED’s. Perspex’s NORMAL LED’s display up to sixteen colors to show which signals are the same (normalled) and which signals are different. The channels that contain the same signal are identified with the same color on the ring of NORMAL LED’s.
The inner circle of LED lights on Perspex’s panel are its CAPACITANCE VANE LED’s. As the capacitance vane in the multiplexer drum passes by each channel’s input vane, the channel’s CAPACITANCE VANE LED is illuminated. The CAPACITANCE VANE LED’s are at full brightness when the capacitance vane is exactly aligned with the channel’s input vane, and the lights fade in or out as the capacitance vane moves toward or away from each input vane.
The Perspex module sends four identical copies of its output channel to the OUT 1, OUT 2, OUT 3, and OUT 4 output jacks. The output signals are clamped at -10.0 volts and +10.0 volts for safety.
In February of 2018, Paul Bristow asked on the VCV Rack Official Facebook group if anyone had created a module with the key functions of the BBC Radiophonic Workshop’s Crystal Palace, and if not would anyone like to try. I agreed to take on the project, and initial versions were developed and reviewed by Paul from February through April. The almost-ready-for-release version was finished in September. Paul has been enormously patient and generous with his time as I worked the kinks out of Perspex, and I am very grateful for his guidance.
Members of the VCV Rack – Plugin Developers Facebook group, including Andrew Belt, Lars Bjerregaard, Eric Sterling, Jeremy Wentworth, David O'Rourke, and Clément Foulc very kindly answered my programming questions. Thanks for your assistance and encouragement, everyone!
Finally, thanks to Dave Young for the invention and construction of the original Crystal Palaces, and to Brian Hodgson and the other members of the BBC Radiophonic Workshop for their unique creations using the devices. The BBC Radiophonic Workshop team has uniquely enriched my life, and I am so grateful for their creativity and imagination.
The development of the Crystal Palace and other devices by Dave Young is documented in the “Early Days” article by Ray White on his BBC Radiophonic Workshop: An Engineering Perspective at whiteflies.org, retrievable from https://whitefiles.org/rws/r02.htm.
Ray White’s images collection at https://whitefiles.org/rwg/ contains numerous photos of the Crystal Palace, with explanatory captions.
The book, Special Sound: The Creation and Legacy of the BBC Radiophonic Workshop, by Louis Niebur (Oxford University Press, 2010) is a fascinating account of the Workshop, and includes brief mentions of Dave Young’s Crystal Palace.
The Radio New Zealand program, “These Hopeful Machines (03 Sep 2013),” includes an interview with Mark Ayers describing the Crystal Palace, as well as a sound clip of the device in use. You can listen to the Crystal Palace segment of the program at https://www.radionz.co.nz/concert/programmes/hopefulmachines/audio/20143127/outtake-the-crystal-palace.
Brian Hodgson’s soundtrack to Doctor Who: The Krotons is available on CD and Digital Download from Silva Screen Records. Information is available at http://www.doctorwhomusic.com/new-classic-who-releasethe-krotons/ and the soundtrack can be purchased through retailers. This disc is a favorite of Paul’s and is definitely worth a listen!
Electronic Sound magazine issue 43, featuring the BBC Radiophonic Workshop’s 60th Anniversary performance at the Royal Albert Hall on May 26, 2018, includes mentions of the Crystal Palace. The print issue is available from https://electronicsound.co.uk/product/issue-43/ for a limited time.
The Science Museum Group's page, ‘Crystal Palace’ Capacitive Fader used in BBC Radiophonic Workshop, has excellent color photos of the Crystal Palace (object number 2012-5118/242/9) in the BBC Heritage Collection at https://collection.sciencemuseumgroup.org.uk/objects/co8241549/crystal-palace-capacitive-fader-used-in-bbc-radiophonic-workshop-sound-device.
Initial public release through the VCV Rack Plugins page.
Updated for VCV Rack verion 1.0. Released through the VCV Rack Plugins page. Compiled with Rack-SDK v1.06.
Updated for VCV Rack verion 2.0. Released through the VCV Rack Plugins page. Compiled with Rack-SDK v2.2.3.