The heart of a classic disco effect: the American DJ RollerTron 250 with DMX protocol

A while ago, I showed you the BrokenSwing 501 analogue disco lighting effect, which is based on two stepper motors and a power-hungry 250 W halogen bulb. Today it’s time for a similar piece of kit – the RollerTron 250 by American DJ. It offers simple control via an external remote (blackout), synchronisation to the beat of the music, as well as digital control via the DMX protocol. The whole unit is housed in a casing weighing 5.4 kg, and an interesting feature is the option to unscrew the mirror head, turning the unit into a standard colour changer.

Even from the outside, the unit looks more modern. The differences compared to the previous model shown are evident at a glance. There are two motors on the outside – one clearly visible, and the other concealed within the mirrored shaft.

At the rear of the unit, we can see the DMX In and Out sockets (standard 3-pin XLR), a 1/4" jack socket for an external controller, as well as a sensitivity control for the built-in microphone and a switch with an integrated 3A thermal fuse.

On the top panel, there is a simple display with three buttons (Function, Up, Down), used to set the DMX address and select the built-in programmes.

For now, let’s take a look inside the bulb – the manufacturer has made things easier by providing a flip-open cover secured with quick-release screws, which is also suspended from a steel cable to prevent it from falling.

The socket holds a standard 24V 250W ELC halogen bulb with a reflector. This particular bulb is present, but unfortunately it is clearly burnt out, as evidenced by the milky-black coating on the glass.


We therefore continue with the dismantling and remove the top cover. The interior here is much more crammed than in the old Trix – the electronics have been split into several smaller circuit boards arranged around the bulb chamber; you can also see an aluminium heat sink on the left-hand side and a simple power supply with a rectifier bridge.

However, the power supply is still based on a mains transformer; I can’t see a switching solution here.

Looking deeper inside, we can see a control board with a microcontroller. A factory sticker bearing the inscription “ROLLER TRON 250” remains on the circuit board, and the date visible there (12/27/2004) clearly reveals the period from which the electronics in this device originate.

Now for the most interesting part – the motor with a metal gobo disc fitted. Brass plates with cut-out patterns have been fitted into the holes in the disc. The mechanism has already accumulated a considerable layer of dust, which is entirely normal for devices that draw in air via a fan.

And that’s not all, because on the other side there’s another motor and a separate colour disc, onto which square dichroic filters have been affixed. Thanks to this setup (independent discs), you can mix any gobo pattern with any colour.

A short video demonstrating how the colour disc works.

Additional photos of the electronics below – you can’t see much, but you can make out the classic through-hole (THT) assembly and the relay A Sanyou 12V power supply (presumably powering the bulb), an LM324N operational amplifier (driving the microphone circuit) and 74HC14 series gates.

Generally speaking, the device works – the display shows addresses correctly and responds to the buttons (as can be seen in the photos), the rollers turn; it’s just that wretched bulb that’s burnt out.

Additional video – reel movement:

Documentation:

Full version attached.

To sum up , this was an interesting glimpse into the inner workings of a classic disco effect. The unit was massive, slightly more complex than the previous one, and once again featured a sturdy casing and clever mechanics providing a whole range of different lighting effects. Once the 24V 250W ELC halogen bulb has been replaced, the unit will likely come back to life and be back in action on the dance floor.
Have you come across this type of equipment, or have you used the DMX protocol ?