RTS PS20 Power supply

PS20 Power Supply

The power supply is the heart of the TW system. It generates DC power to drive all system components, with the exception of self-powered user stations, and also sets the necessary impedance (200 ohms) for the audio signal.
The PS20 is a new power supply from RTS and offers twice the power output of the previous PS31 power supply in a compact, 1U, half-rack format.

Features

• Selectable mode operation (RTS 2 channel, RTS 4 channel and Clear-Com mode)
• 1.8 Amps (maximum) per channel
• Switchable 200 ohm (for standalone use) or 400 ohm impedance (for linking to a second RTS power supply) on each channel
• Audio Linking to a second PS20 is via two 6.3mm stereo jack sockets on the rear panel
• A 3-pin XLR connector on the front panel allows connection of a RTS beltpack or user station to monitor one or both channels
• Front panel-mounted status indicators for each channel illuminate green during normal operation but turn red during a channel overload condition. Output current is automatically limited during an overload
• Normal operation is restored when the overload is removed
• Fan assisted cooling helps minimise the risk of over-heating
• Programme audio input is via a 3-pin female XLR on the rear panel
• Programme audio may be assigned to channel 1, channel 2 or both
• Programme audio assignment and level are controlled from the front panel
• Four 3-pin XLR outputs on the rear provide connection to the TW line

The most significant benefit of the RTS Two Wire intercom system is its ability to provide 2 channels of intercom down a standard mic cable. Other systems can provide only a single channel without resorting to special cables.
To enable two channels of intercom audio to be sent down a standard microphone cable, one of the audio channels must also carry DC voltage to power the system. This makes RTS different to other intercom systems and necessitates the use of a two to four wire convertor if equipment from other manufacturers is to be linked.

RTS wiring convention has pin 2 carrying 30V DC plus channel 1 audio (commonly referred to as the ‘Wet’ channel) while pin 3 carries channel 2 audio only (the ‘Dry’ channel). Pin 1 is common to both audio and DC.
Having DC power on pin 2 only can lead to confusion when using RTS SAP matrix boxes to increase the number of available intercom channels to more than the standard two. While these matrixes are an excellent and cost effective way of creating quite complex intercom systems, the unwary can easily end up with some circuits operating fully while others are dead due to lack of DC power!

The PS20 differs from other RTS power supplies in its ability to provide 30V DC on both pins 2 and 3 (when operated in RTS two channel mode). This cures the ‘dead channel’ syndrome and makes trouble free operation of the SAP Matrix panels available to those of us who have not studied advanced mathematics. The presence of DC voltage on pin 3 will not harm RTS user stations as they are fully DC protected on both channels.
The PS20 reverts to DC power on pin 2 only when in RTS 4 channel mode.

A useful feature is the PS20’s ability to supply power to the majority of intercom systems from other manufacturers. Switching to Clear-Com mode puts 30V DC down pin 2 and audio on pin 3. Pin 1 is common.

When using a large number of beltpacks or user stations, additional system power may be necessary. Two PS20 power supplies can operate together to double the power capability. A pair of standard stereo jack sockets on the back of the power supplies allow audio linking of the two units, if required.
The ‘Input Select’ switch on the rear panel toggles between 200 and 400 ohms. If the PSU is being used alone, 200 ohms should be selected. When operating with another RTS power supply select 400 ohms.