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An insulating boot should be fitted onto the back of the fuse holder, which should be fitted with a 5A anti-surge fuse. If the fuse is removed and the lights are unplugged you can work on the PCB while the mains connected with reasonable safely - this may be useful for fault-finding.

Two 1/4" mono jack sockets are used for the audio input. These MUST be the plastic bodied type so that no connection is made between the speaker wiring and the earthed case (to prevent hum loops or damage to the amplifier). Two sockets are connected in parallel so that this unit may be connected between the amplifier and the speakers using two leads. This arrangement is also fairly standard with disco equipment. Use 6 Amp wire for the links between the two sockets because they have to carry the full speaker current. If your equipment uses a different type of connector for the speaker wiring (such as 3 pin Cannon) you could fit these to this unit instead.

Speaker leads have to handle significant current and should be made using round 2 core 6 Amp mains flex (flat cable kinks too easily). I use the orange cable intended for garden power tools, so it can be readily distinguished from other audio cables fitted with jack plugs. Use metal jack plugs - the plastic ones break far too easily. Since all the controllers will normally be stacked up in one place, a number of short speaker leads are useful for linking them together.

The above information assumes you are using this controller with professional disco equipment. I have given more detail than is strictly necessary to build this controller, in the hope that it will be of use to those readers who may be just starting to run a small mobile disco.

If you are building this unit solely for home use you can use whatever connectors take your fancy - as long as they are suitably rated for the voltages and currents involved. You could save a significant amount of money by building the controller into the light box - you save the cost of a case, some connectors and some multi-core mains cable.

Testing
The unit should be tested initially with the lamps disconnected. Do not fit the fuse in the fuse holder yet. Set VR1 fully clockwise and connect the unit to the mains and your amplifier.

When you play some music, the LED's should flash in a manner similar to a VU meter. Reduce the setting of VR1 such that the top LED lights only occasionally. Now alter the volume on your amplifier. After a second or so (while the automatic level control sorts itself out) the lights flashing should revert to the same level.

Now switch off and fit the fuse. Connect some lamps to the outputs and switch back on. The whole PCB is now live, so do not touch it! The lamps should flash in time with the LED's on the appropriate channel. If you have not assembled the light box yet you may find it easier to connect a table lamp to each output in turn (switching off while you change the connections).

Light Box Construction
The construction of the light box depends to a great extent on the resources available and your own ability. The suggestions given here may be used as a guide.

If you are running a mobile disco you will need to make the light boxes fairly solid. It will get a battering - no matter how gentle you plan to be. There will be evenings when you need to clear everything up and get out within ten minutes, because the landlord or whoever wants to lock up and go home!

Firstly decide whether you want the light box vertical or horizontal. If you are running a disco and choose a vertical arrangement, you will probably need to build two if you want your setup to be symmetrical - which of course costs twice as much. Also bear in mind that vertical boxes could be somewhat unstable and prone to being knocked over, unless you make it fairly wide, deep and heavy.

The controller will drive two light boxes without problems. Alternatively, if your disco is stereo, you could make two controllers (possibly in one case with a dual pot), and drive each light box separately. In this case you may need to reduce the value of C6 to allow some more mid-range through otherwise the two units will appear to be doing the same thing!

With a horizontal light box you could position it centrally, above or below your name sign. You could even put the name of your disco on the front of this light box, and kill two birds with one stone!