Abstract: A head for a scanning probe microscope comprising a tuning fork (130) with an SPM tip (134) attached to one prong of the tuning fork. An AC signal (Vin) generated by oscillation of the tuning fork is supplied by a pair of electrodes on the tuning fork to input terminals (110 and 112) of a source-follower circuit comprising a dual-gate GaAs-MESFET (114), the gates (G1, G2) of which are connected in parallel to one of the pick-up electrodes via one of the input terminals (110), the other of the pick-up electrodes being earthed via the other of the input terminals (112). The signal (Vin) is processed by the circuit and supplied to two output terminals (126 and 128) as an output signal (Vout). The megaohm output impedance of the tuning fork is thus translated into an output impedance of the order of a hundred ohms, thus improving signal transfer efficiency from the head to an external signal amplifier.