Multichannel power amplifying

#The invention relates to power amplifiers, and more particularly to multichannel power amplifiers. The power distribution capacities of multichannel amplifiers are typically “rated,” on a “per channel” basis, usually on an “all channels driven” basis; that is, each of the four channels has a power distribution capacity of the per channel rating when all the channels are driving an electrical load. The total power distribution capacity of the amplifier system (often unspecified in a conventional multichannel amplifier) is the sum of the “per channel” ratings. For example, a four channel amplifier may be rated as 100 watts per channel, that is, each channel has a power distribution capacity of 100 watts, and the total rating, or power distribution capacity of the multichannel amplifier is 400 watts. To use all 400 watts of power distribution capacity, each channel would have a total load of 100 watts, but no more.

#It is an important object of the invention to provide an improved multichannel power amplifier.

#According to the invention, a multichannel electrical power amplifying system is constructed and arranged to distribute electrical power of amount P to an electrical load coupled thereto. The system includes a plurality n of power amplifier channels, coupling the power amplifying system to a portion of the electrical load, each of the amplifier channels for distributing a portion of the electrical power P to a portion of the electrical load. Each power amplifier channel haS a power distribution capacity, and at least one of the power amplifier channels is constructed and arranged to have a power distribution capacity significantly greater than 2 P n

#FIG. 1 is a block diagram of a four channel power amplifying system according to the invention;

#FIG. 2 is a thermal model of the amplifying system of FIG. 1;

#FIG. 3 is a top plan view of a heat sink for the amplifying system of FIG. 1, showing the footprints of heat producing elements of the amplifying system of FIG. 1;

#With reference now to the drawing and more particularly to FIG. 1, there is shown a block diagram of an audio signal power amplifier system incorporating the invention. A multichannel power amplifier system 10 includes a common power supply 13 (that is, a power supply that powers all channels of the power amplifier system) coupled to four high voltage, low current power amplifiers 12-1-12-4 (hereinafter power amplifiers, and sometimes referred to as constant voltage, distributed amplifiers) which are coupled to four audio output lines 14-1-14-4. Each of the audio output lines 14-1-14-4 has audio devices 16-1-16-4 coupled to it. Audio signal processor and router 18 has a plurality of input terminals 19-1-19-4 and a plurality of multiple output terminals 20-1-20-4. Each of the output terminals 20-1-20-4 is coupled to one of the power amplifiers 12-1-12-4. The power amplifiers 12-1-12-4 are mounted on a single heatsink 22. Optional fan 24, if necessary, is positioned so that it directs a cooling airflow across heatsink 22.

#In operation, audio signals are received at input terminals 19-1-19-4 and routed to output terminals 20-1-20-4 and conducted to any one of power amplifiers 12-1-12-4, which amplify the audio signals and transmit them to electrical loads 16-1-16-4, typically electroacoustic transducers, which transduce the amplified audio signals to sound waves. Power supply 13 converts line AC voltage current to a DC voltage suitable for powering 70.7- or 100-volt low-current direct-drive power amplifiers; typically ±130 or ±170 volts, respectively, is suitable. The output of power supply 13 is conducted to power amplifiers 12-1-12-4. Heatsink 22 conducts heat away from power amplifiers 12-1-12-4. If passive cooling is insufficient to conduct the heat away from the heat sink, optional fan 24 directs heat away from heatsink 22 to the external environment.

#In one embodiment, the total power rating of the power amplifier system is 400 watts; that is, the power amplifier system is constructed and arranged to have a power distribution capacity of 400 continuous average watts. The audio signal processor and router18 may be a conventional analog or digital signal processor and router having multiple input and output channels, in this example four input and four output channels; the number of input channels does not have to be equal to the number of output channels. Power supply 13 is a conventional power converter, constructed and arranged to convert line AC voltage to ±130 or ±170 volts and to supply power equal to the total power rating of the power amplifier system, in this embodiment 400 watts (plus any power that is dissipated in the amplifiers). Power amplifiers 12-1-12-4 may be 70- or 100-volt high-voltage low-current power amplifiers, each rated at up to 400 watts. Power amplifiers 12-1-12-4 may be linear amplifiers, however in an exemplary embodiment, they are switching amplifiers, each containing two field effect transistors (FETs). Power amplifiers including switching amplifiers are advantageous over linear amplifiers in a system described by FIG. 1, because they are more efficient than linear amplifiers, particularly in the case of high power loads, and low power (or no) loads. Power amplifiers 12-1-12-4 are directly coupled to audio output lines 14-1-14-4; that is, there is no intervening transformer coupling power amplifiers 12-1-12-4 and audio output lines 14-1-14-4. Output lines 14-1-14-4 couple power amplifiers 12-1-12-4 to audio devices 16-1-16-4, respectively. Audio devices are shown as single transducers, however typically each power amplifier is coupled to a plurality of conventional loudspeakers constructed and arranged to operate at the output voltage of the power amplifiers. The power ratings of each of the individual power amplifiers 12-1-12-4 can be substantially greater (for example at least twice) the total power rating of the amplifier system 10 divided by the number of channels and up to a number equal to the total rating of the amplifier system. So, for example, in this embodiment, the power rating of the four channel power amplifier system 10 is 400 watts, the rating of each of the power amplifier channels is much greater than 100 watts, in this case 400 watts. Additional details of the power amplifiers 12-1-12-4 are shown in FIG. 4.