The degree of structural damage and phase transformations in metallic materials can be monitored by measuring the internal damping of materials, which corresponds to the absorption of mechanical energy in the internal structure of the material when it is under mechanical stress. Damping is a complex variable linked to a number of factors, which are related to modifications in the material structure, the temperature and external magnetic field, as well as the amplitude of the applied mechanical force, its frequency, displacement, deformation and the number of loading cycles. The paper proposes a compact instrument for standard laboratory measurements determining the value of the internal damping, utilizing a monolithic impedance converter. This enables the measurement of a complex electrical impedance of the ultrasonic piezo – transducer within a defined frequency range around the resonance of a mechanical specimen, automatic tracking of an amplitude drift and phase of the resonance curve.