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Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the RMS voltage and, hence, the mean power to the lamp, it is possible to vary the intensity of the light output.

Modern dimmers are built from silicon-controlled rectifiers (SCR) instead of variable resistors, because they have higher efficiency. A variable resistor would dissipate power as heat and acts as a voltage divider. Since a silicon controlled rectifier switches between a low resistance "on" state and a high resistance "off" state, it dissipates very little power compared with the controlled load.

For more information on dimmers in general, consult other sources, such as Dimmer on Wikipedia.

Venue One

The current system in Venue One is the Jands Rack.

The Jands Dimmer system is a 48 way dimmer, system bought by the union in December 2010 to replace the old Betapack I dimmer racks and demux. It is located in the stage left wing next to the distro and rubber box.

The System

The Dimmer system itself is not a particular make or model, but rather 4 Jands FPX 12 channel dimmers installed into a flight case with power distribution, a patch panel, soca panel, Optosplitter and cooling system.

Jands FPX 12 Channel Dimmers

Each Jands FPX dimmer, or module, is a 12 channel unit. Each of the 12 channels has an individual circuit breaker. The system can be programmed with a basic chase, or controlled via DMX. Channels 1-4, 5-8 and 9-12 are each on a separate phase.

The dimmers are daisy chained together through DMX for control information, and each dimmer has a switch for activating a built in DMX terminator - only the last dimmer should have this switch in the Terminate position.

If the dimmers are being operated on the same universe as the intelligent heads, they should have their starting addresses set, from Module 1 (top) to Module 4 (bottom), to 1, 13, 457 and 469. In all other cases, they should be 1, 13, 25 and 37 respectively.

The manual for these units is available from the Jands Website.

Power Distribution

The Jands dimmer system requires 125A three phase power, supplied via the Powerlock inputs on the rear, under the soca panel. These connectors are provided by a jump from the 125A ceeform, which comes from the Understage Isolators.

At the front of the unit, there are circuit breakers - one for each module, as well as the "auxiliary" 16A ceeform outputs on the back. We don't normally use these outputs, so when powering up the Dimmer Racks there is no need to switch the auxiliary section on. They have however been used in the past when large amounts of hire equipment have been brought into the venue. There is also a circuit breaker protecting the DMX feed from overcurrent if a fault develops along the cable run.

Patch Panel and Socapex

The top panel of the rack is called the patch panel. Each pair of sockets at the front of the panel matches a channel on a dimmer module, while each individual socket at the rear of the panel matches a single channel on a socapex. In this way, it is possible to link two luminaires to one dimmer channel - though care may need to be taken to ensure you don't draw too much current: each channel is rated at 10A, allowing for around 2300W of lantern.

The rear of the rack comprises the socapex panel, where each numbered socapex output matches the patch sockets at the rear of the patch panel. Each socapex is capable of carrying 6 channels of power, and there are 16 socapex outputs.

There is no need to worry about cross-phasing in this system, unlike with the Betapacks.

Venue Two

The current system in Venue Two consists of two Zero88 Betapack 2s and one UNKNOWN.

Dimmers/Zero88 Betapack 2

Past Systems