| 摘要 |
PURPOSE:To attain no adjustment of a bias current in a recording mode by providing a means detecting automatically a recording bias current and a means controlling the bias current in accordance with the output. CONSTITUTION:In a reproducing mode, the reproduction output of an audio head 4 is inputted to a reproduction equalizer amplifier 2 without being affected by a bias trap 7, while in a recording mode a recording current where the output of a recording amplifier 1 and that of a bias generating circuit 3b are superimposed is flowed through the head 4 and a transistor 6. A signal in an audio frequency band is cut by the trap 7, and only a bias signal is detected by a diode 8 and fed back to the generating circuit 3b. Accordingly, since the bias current value is detected and controlled, the bias current can be automatically controlled even when the impedance of the head 4 fluctuates. As a result a cost price is cut down, and production efficiency can be improved.
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