Background Art A distributed stereo system is described in PCT/AU98/00647. In this system the source and remote amplifier and speaker sets are interconnected using Category 5 four pair twisted cable (or a higher category cable), and this cable transmits line level signal and power to the remote amplifier and speaker sets. It may also carry status and control signals back to the source. This system is known as'A-BUS'.

There are several advantages to using Category 5 cable described in that patent application, but one of the drawbacks is its limited power capacity. This is especially noticeable with long cable runs which may be required in a distributed audio system.

For instance, A-BUS provides a system voltage of 24 volts, and the audio signals injected at the source are at about 24 volts. At the remote end, the remote amplifier operates at the system voltage and when it receives the signal it also draws current through the cable depending upon the volume required. Because of the high resistance of the cable over long runs, attempts to increase the sound volume draw more current and increase the voltage drop along the cable. At maximum volume the voltage may drop from 24 volts at the source end of the cable to 18 volts at full volume over a distance of just 30 metres. This has the effect of reducing the available power of the system substantially. The usual way to address this problem is to increase the voltage at source, but this has been found to be counterproductive because of the small gauge of copper wire used in the category 5 cable.

Summary of the Invention In a first aspect the invention is a distributed stereo system comprising: one or more remote stereo amplifier and speaker sets for the broadcast of stereo audio signals ; a local source of stereo audio signals and a mains operated electrical power supply to provide audio signals and power at a system voltage to the remote amplifier (s), respectively;

a category 5 four pair twisted cable interconnecting the remote amplifier (s) and the signal source and power supply, which cable provides, in separate twisted pairs of the cables, right channel audio signals, left channel audio signals, and DC power; wherein, at least one remote amplifier is configured to deliver full power output at a received voltage level less than the system voltage and includes a regulator to regulate the received voltage down to that level.

This arrangement takes into account the problems of voltage loss along a cable by using an amplifier that delivers full output at only, for instance, 15 volts with a maximum current load of 1.6 Amps. The system voltage may remain the same as the original at 24 volts. To create a stable power source the regulator may be placed at the remote amplifier end of the cable.

Of course the system is not limited to the use of an amplifier that delivers full output at 15 volts, i. e. a higher voltage could be regulated down the line. For instance the system voltage may operate at 35 volts and the amplifier chip may be rated at 24 volts. The regulator would then operate to regulate the voltage input to the amplifier down to 24 volts.

The remote amplifier can deliver its full output of 12 W+12 W 10% THD and 10 W+10 W 1% THD over 30 metres. The overall result is an increase in power output of about 30% without power loss using category 5 cable up to 30 metres. The system may also provide reliable amplification up to about 50 metres.

The right channel audio, left channel audio and DC power may be provided in different twisted pairs of the cable.

The cabling is capable of adapting to new technologies and system upgrades without the need to re-cable when upgrades are required; for instance, it can also be used to transmit digital audio, video and control commands. Thus, the stereo amplifier may be implemented as a digital chip to deliver more power at lower current drain and less voltage, thereby enabling longer lengths of cable.

In a second aspect the invention concerns a remote amplifier for a distributed stereo system, the remote amplifier comprising: an input that receives power from a remote power source via a cable; an output to which a pair of audio speakers is connectable ; and a regulator that regulates power supplied to the input to maintain a constant voltage at the input regardless of losses in the cable.

Brief Description of the Drawings An example of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a schematic illustration of a distributed stereo system ; and Fig. 2 is a circuit diagram of a remote amplifier of the system of Fig. 1.

Best Modes of the Invention In figure 1, the distributed stereo system 10 includes a single remote stereo amplifier 12 and speaker set 14 for the broadcast of stereo audio signals. The amplifier 12 and speakers 14 are located in a first room. A source of stereo audio signals 16 is housed in a second room, remote from the first room. A mains operated electrical power supply 18 provides the audio signals and power at a system voltage to the remote amplifier 12. The source of stereo audio signals 16 includes a CD player 19, a tape recorder 20, a DVD player 22 and a source selector 24.

The amplifier 12 is connected to the signal source 16 and power supply 18 by means of a category five, four pair twisted cable 26. One of the twisted pairs provides the right channel audio signal from the source 16 to the amplifier 12, another pair provides the left channel audio signal from the source 16 to the amplifier 12, and a third pair delivers power to the amplifier 12 from the power supply 18. The amplifier 12 is designed to deliver full power output at a received voltage level less than the system voltage and includes a regulator to regulate the received voltage down to that level.

Amplification may be controlled by a hand-held remote controller 28 which transmits infrared signals 30 to a receiver 32. Infrared signals may be transmitted back to the source 16 using the fourth twisted pair in the category five cable 26. The infrared signals may be used to control the source 16 directly. Optionally, they may be used to retransmit the control signals using transmitter 34 to an infrared receiver 36 associated with the source.

The remote amplifier 12 includes an amplifier chip 40 (figure 2). The chip 40 operates with a power supply at 15 volts. A regulator 42 is included to regulate the voltage input to the amplifier 12 and compensates for any overvoltage received. The amplifier can amplify signals with high-fidelity up to 12 W+12 W 10% THD and 10 W+10 W 1% THD over about 30 metres. The system voltage output by the power supply 18 remains at 24 volts. It will be appreciated that the amplifier 12 could operate at a voltage higher than the 15 volts in which case the regulator 42 is selected accordingly.

The regulator 42 is a 15 volt, 3 Amp unit arranged at the remote amplifier end of the cable 26.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.