Ac bias control recording system and apparatus in a magnetic recording apparatus

Claim 1

In a magnetic recording apparatus, an AC bias control recording system comprising a transmission line for transmitting an input signal to be recorded from an input signal source, means for generating a bias signal, a magnetic medium and means for superposing the bias signal upon the signal to be recorded and for magnetically recording said signal to be recorded on said magnetic medium, low pass frequency filtering means for filtering a low frequency signal component below a predetermined frequency from the input signal to be recorded, means coupled to said filtering means for obtaining a control signal representative of the magnitude of said low frequency signal component, said means coupled to said filtering means for obtaining the control signal comprising means for forming a control signal of DC voltage which is obtained by rectifying the output low frequency signal component from said filtering means, and control means responsive to the level of said control signal for maintaining the value of the bias signal relatively small when the input signal includes no low frequency signal component below a predetermined level and for increasing the value of the bias signal current to a relatively large value only when the input signal includes a low frequency component above said predetermined level, said control means comprising a control element which changes its internal resistance upon receiving said control signal and variably controls the amounts of attenuation of the bias signal current passing said control means.