Abstract: The present invention provides a magnetic recording and reproducing apparatus having an amplifier apparatus, which is switched from a recording state to a readout state based on a control signal, reads out a signal containing a servo signal by the signal readout means, and includes the amplifier apparatus for amplifying the signal with an amplifier and outputting the amplified signal. In addition, the amplifier apparatus filters the signals by the filtering means that allows the high frequency portion of signals to pass through with a first cutoff frequency during a first prescribed time period after the readout state has been initiated; a second cutoff frequency that is lower than the first cutoff frequency during a second prescribed time period after the first prescribed time period has passed; and a third cutoff frequency that is lower than the second cutoff frequency after the second prescribed time period has passed.

Abstract: A bias circuit for a magneto-resistive head having a bias current output circuit for flowing a bias current through a magneto-resistive head, and a feedback circuit for controlling the bias current from a bias current output circuit by detecting voltage variation across the magneto-resistive head so that a voltage across the magneto-resistive head becomes a predetermined value. The bias current output circuit comprises a regulating circuit for regulating an operation of the bias current output circuit in the bias current output circuit, a control circuit for controlling the regulating circuit to be in a predetermined condition, and a switching circuit for switching a read/write condition for activating the control circuit for the regulating circuit in a non-read condition of the magneto-resistive head. The regulating circuit includes an oscillation suppressing capacitor; and the control circuit for the regulating circuit is a charging circuit for the oscillation suppressing capacitor.

Abstract: Provides a magnetic recording and reproducing apparatus having an amplified apparatus, which is switched from a recording state to a readout state based on a control signal; reads out a signal containing a servo signal by the signal readout means; and includes the amplifier apparatus for amplifying the signal with an amplifier and outputting the amplified signal; and filters the signals by the filtering means that allows high frequency part of signals to pass through with the first cutoff frequency during the first prescribed time period after the readout state has been initiated; the second cutoff frequency that is lower than the first cutoff frequency during the second prescribed time period after the first prescribed time period has passed; and the third cutoff frequency that is lower than the second cutoff frequency after the second prescribed time period has passed.

Abstract: A bias circuit for a magneto-resistive head having a bias current output circuit for flowing a bias current through a magneto-resistive head, and a feedback circuit for controlling the bias current from a bias current output circuit by detecting voltage variation across the magneto-resistive head so as a voltage across the magneto-resistive head to be a predetermined value, comprises a regulating circuit for regulating an operation of the bias current output circuit in the bias current output circuit, a control circuit for the regulating circuit for controlling the regulating circuit to be in a predetermined condition, and a switching circuit for switching a read/write condition for activating the control circuit for the regulating circuit in a non-read condition of the magneto-resistive head. The regulating circuit includes an oscillation suppressing capacitor; and the control circuit for the regulating circuit is a charging circuit for the oscillation suppressing capacitor.