LX-800 LIGHTING SYSTEM

There is, and always has been, a marked lack of good, inexpensive lighting controllers for small theatre groups or musicians.  The LX-800 Lighting System was designed with these applications in mind.

It is an ambitious project, but if you attack it in a logical and thorough manner, you'll have no problems putting it together and making it work.  Over the years since initial publication, there have been many enquiries and quite a few people have built the unit - either complete as described, or just the sections they needed.  There have been several updates since July 2000, and there may be some more coming (as of April 2015).  One addition is likely to be a trailing-edge dimmer option, which is much kinder to lamps that use an electronic supply (in particular, LED lighting).  The TRIAC dimmers shown should not be used with any electronic load!

Note: The mains system in South Africa (the origin of the project) is a 240VAC 50Hz supply, fed domestically from 3-pin 16A sockets.  All mains voltage references in the text will imply this supply voltage.  If your mains supply differs, it is generally a simple matter to modify the circuits to suit.  The supply voltage in Australia (and most European countries) is nominally 230V, 50Hz, but it can vary from a little under 230V to a typical maximum of 250V (some locations may experience higher voltages - up to 260V).

• Two banks of eight channel controllers, each bank with its own master fader.
• Eight-channel sound-to-light (S2L) converter *
• Eight-lamp chaser with level control *
• Strobe light controller *
• Eight on/off remote switches
• Eight flash buttons

The items marked with * are optional.  If desired, the main unit can be built and these added later as time and finances permit.

In the ideal situation, each module will control its own power box, but this can be a tad expensive for struggling musicians and amateur theatrical groups :-).  So - a compromise design evolved.  The simplest system would comprise one console (obviously) and one power box.  All the module outputs are linked back through jumper cables on the rear panel.  What this achieves is that the larger signal takes precedence over the other.  Neat hey?  So- if you've got some nice, low, mellow mood lighting on the band, and you turn up the chaser level, for instance, then the lamps will happily chase along, but their brightness will never drop below that of the console fader settings.  Clear?  I hope so.

Likewise, the chaser could be switched off and the sound-to-light turned on.  In this case, the mood lighting will determine the minimum brightness, and the S2L will 'bounce' the light level in time to the music.  Clearer?  Read on, all becomes clear as you get deeper into the project ... I hope.

The chaser and the strobe can be triggered from a bass-line extractor which, as its name implies, extracts the bass beat from the audio feed.  This circuit is more complex, perhaps, than it could be, but it works like a charm - no double-triggering, which is the bane of simpler circuits.  Both of these modules can also free-run from their own oscillators.

Power Unit

• Eight TRIAC-controlled zero-crossing-triggered phase controlled output: 240V / 110VAC 10A each.
• Console power supply

Although each channel is rated at 10A, simple mathematics will indicate that with all channels running at maximum output, the mains supply will have to supply 80A.  Way beyond the capabilities of wall plugs! The output rating is there a safety measure - offering plenty of overhead and allowing everything to run cool and calm.

The author used common PAR38 floods and spots, which for smaller venues are quite adequate.  These lamps are rated at between 80 and 150 watts, so a fair number can be connected up without overloading the supply.

Circuit Description

As I said, this is an ambitious project, and as such has a fair amount of circuit complexity.  The easiest way to present the whole thing is to describe it the way I designed it - piece by piece - and then show you how the whole thing goes together.

Before heading off to the next section, though, here's a (revised) drawing of the console.  Click on the image for a larger view.

On the extreme left is a column of switches - toggle switches (or you could use push-on/push-off if you prefer) with indicator LEDs. Then comes the dimmer section itself.  There are two banks of 8 slide controls.  Right at the top is a row of 8 flash buttons. The two controls to the right of the bottom row are the channel masters.  The switch between A&B reverses the B fader so that down is maximum.  This allows cross-fades to be made by moving both masters together. The column of controls on the right of the console are as indicated, from bottom to top, Sound to Light (S2L) level control, bass-beat trigger level, strobe and chaser routing switches (free running - set by speed control, or controlled by the S2L circuit), chaser level control, and lastly the chaser and strobe speed control.

I recommend that you look at the console layout above carefully, as much of the circuitry you encounter on following pages will make a lot more sense when you can see exactly where it fits into the overall scheme.  The drawing has recently been re-drawn to make sure that everything you see on the panel is reflected in the circuits (and vice versa).  An overall understanding of the operational controls and the underlying circuits will go a long way towards a full appreciation of the project.

The power-control section is in a separate housing and connected to the console by a multi-core cable.  Details will be given a bit later in the article.

The next few pages will display schematics of the circuitry.  The construction page will show how it all goes together.  If you want to build the LX-800, the boards will eventually be available, but none are ready for sale at this time.  The circuitry can be built on Veroboard (with the exception of the mains switching), which is not as neat as a PCB, but will work just fine.

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