Abstract: A defect-sensing device for a test object, e.g. for detecting cracks in metal bodies with the aid of the eddy-current technique, has improved phase-selective properties by adding at least one product and/or quotient former to the signal processing equipment. The output signal from an ordinary phase-controlled rectifier can be substantially described via sin .alpha. and/or cos.alpha. functions in which indicates the phase position of the control signal in relation to the input signal. By multiplying sin.alpha. by cos .alpha. sin 2.alpha. cos 2.alpha. functions are obtained which in turn can be multiplied to obtain the function sin 4.alpha. corresponding to narrow sensitivity lobes in the transducer's impedance plane, thus permitting effective separation of the various types of vector signal resulting from detectable defects.