Separation band detecting circuit in an automatic program selection record player

A circuit for detecting separation bands between bands recorded on a record, said detecting circuit being in an automatic program selection record player, said record player having a photodetector and a tone arm which move together, said photodetector having a light-emitting element for directing light against the surface of the record and a photosensitive element for receiving the light which is reflected from the record surface and for producing an output signal which is in accordance with quantity of the reflected light which is received by said photosensitive element, said detecting circuit comprising:

• an operational amplifier having first and second input termnals, said first input terminal being supplied with the output signal of said photodetector, said output signal including a D.C. component;
• and
• a time constant circuit having a predetermined time constant and including a diode which is coupled between said first and second input terminals of the operational amplifier, said second input terminal being coupled through said time constant circuit to a potential source;
• means including said time constant circuit for supplying a threshold voltage to said second input terminal of the operational amplifier, said threshold voltage undergoing a gradual voltage level change with said predetermined time constant to follow a voltage level change in the output signal of said photodetector, and
• means including said operational amplifier for inverting an output signal in response to a sudden large level change in the output signal of said photodetector, said sudden large level change occurring with a period which is shorter than said predetermined time constant and accompanying a voltage change to a voltage level which exceeds the level of said threshold voltage.