writing of data on a storage disk by an inductive magnetic transducer is modulated by write driver circuitry that includes a supply voltage as low as three volts provided by a source referenced to ground , and a bias current source connected to either the supply voltage source or ground . two bias control switches respectively direct the bias current to one or the other of two current gain circuits according to whether a positive or a negative input terminal has a preselected polarity . the gain circuits selectively respond to the bias currents supplied by the associated control switch for amplifying the bias current to remove a write current from a respective associated terminal of the transducer . two current source switches connected to a respective one of the input terminals and to a respective one of the terminals of the transducer selectively allow and prevent the write current from flowing into the respective associated terminal of the transducer depending upon which of the input terminals has the preselected polarity . when data is not being written by the transducer , a controllable reference voltage circuit maintains the transducer at a potential at least as negative as ground to prevent electro - erosion of the transducer ; and this circuit also is preferably connected to both gain circuits to prevent them from saturating .