Patent EP-0447347-A1 (EP)
Inventor: JORGENSEN BENT
IPC: H04H60/04
Filed: 1991-03-12
Abstract: An audio signal switching system comprising: 
   a first plurality of an input amplifier means, each of said input amplifier means having a first transformer means and a first buffer amplifier means, said first transformer means having a transformer input and a transformer output constituting a balanced input and an unbalanced output, respectively, said first transformer means receiving a balanced input signal at its transformer input, converting said balanced input signal into an unbalanced input signal and outputting said unbalanced input signal from its transformer output, said first buffer amplifier means having an amplifier input and an amplifier output, said amplifier output of said first buffer amplifier means constituting an output of said input amplifier means, said amplifier input of said first buffer amplifier means being connected to said transformer output of said first transformer means, and said first buffer amplifier means receiving said unbalanced input signal from said transformer output of said first transformer means at its amplifier input, amplifying said unbalanced input signal and outputting an amplified and unbalanced signal from its amplifier output, 
   a second plurality of an output amplifier means, each of said output amplifier means having a second transformer means and a second buffer amplifier means, said second transformer means having a transformer input and a transformer output constituting a grounded input and an ungrounded output, respectively, said transformer input of said second transformer means constituting an input of said output amplifier means, said second transformer means receiving an output signal at its transformer input, converting said output signal into an ungrounded output signal and outputting said ungrounded output signal from its transformer output, said second buffer amplifier means having an amplifier input and a pair of symmetrical amplifier outputs, said second buffer amplifier means receiving said ungrounded output signal from said transformer output of said second transformer means at its amplifier input, amplifying said ungrounded signal and outputting an amplified ungrounded and symmetrical output signal from its pair of symmetrical amplifier outputs, 
   switching means for interconnecting at least a single output of a specific input amplifier means and at least a single input of a specific output amplifier means for inputting said amplified and unbalanced signal from said specific input amplifier means to said specific output amplifier means, and 
   a switch mode power supply means comprising an oscillator means generating an oscillator signal, and an output power means receiving said oscillator signal from said oscillator means and outputting a power oscillator signal, 
   each of said output amplifier means comprising a separate switch mode power supply means receiving said power oscillator signal from said output power means of said switch mode power supply and including a separate switch mode power supply transformer means, said second transformer means and said switch mode power supply transformer means of each of said output amplifier means galvanically separating said pair of symmetrical outputs of said second buffer amplifier means of each of said output amplifier means from each other and from said outputs of said input amplifier means, respectively. 
     The invention makes it possible to provide an audio signal switching system, which allows a large number of balanced and/or ungrounded inputs to be switched to an extremely large number of balanced and/or ungrounded outputs in an extremely compact system.