Protective circuit for a direct-coupled amplifier

A protective circuit for a direct-coupled amplifier and for a load device connected to said direct-coupled amplifier, said direct-coupled amplifier comprising:

• a positive and a negative power sources;
• two output transistors connected to said positive and negative power sources, respectively;
• series-connected two resistors defining an intermediate point therebetween at which substantially zero voltage prevails when said direct-coupled amplifier is functioning normally, and being interposed between said two output transistors;
• and
• an output terminal interconnecting said intermediate point and said load device;
• said protective circuit comprising:
• a first low pass filter connected to the junction between one of said output transistors and said series-connected two resistors;
• a second low pass filter connected to the junction between the other of said output transistors and said series-connected two resistors;
• a differential amplifier having two inputs connected to the output of said first and second low pass filters, respectively;
• and
• means connected to the output of said differential amplifier for isolating said intermediate point from said output terminal in response to the output of said differential amplifier.