| 摘要 |
PURPOSE:To prevent an increase in noise level with a bias magnetic field by allowing a muting circuit to cut off not only a signal current, but also a bias current when no signal is recorded. CONSTITUTION:During sound recording, the signal current is passed through a sound recording amplifier 1 and a bias trap 3 and applied to a sound recording head 6 through a muting circuit 2' while superposed upon a bias current. The muting circuit 2' cuts both signal current and bias current in muting mode, so neither current is applied to the sound recording head 6. Therefore, a magnetic tape is free of bias-recorded residual magnetism because any magnetic field variation is not caused by the sound recording head 6 after the erasure of a DC or permanent erasing head 5. |
