Self-sensing actuation (SSA) is a technique to use a single piezoelectric actuator as both an actuator and a sensor simultaneously. A self-sensing actuation circuit is used to extract a voltage generated by a piezoelectric actuator from a control voltage. However, the SSA circuit must be balanced to obtain an accurate sensing voltage. This paper describes an effect of an unbalanced SSA circuit on the sensing voltage output. The SSA circuit is connected to a piezoelectric system to apply the control voltage and measure the generated voltage simultaneously. The unbalanced SSA circuit is configured by designing an equivalent capacitance parameter to be not equal to a piezoelectric capacitance. The unbalanced SSA circuit effects is evaluated in terms of the step response and the frequency response. An experiment is conducted in an open-loop system and a closed-loop system. In the open-loop system, the sensing voltage is observed when the control voltage is applied to the piezoelectric actuator. In the closed-loop control system, a positive position feedback (PPF) controller is used for vibration control at a resonant frequency of the piezoelectric system. Experimental results show that the unbalanced SSA circuit causes the sensing voltage error when the amplitude of the control voltage is larger than the amplitude of the voltage generated from the piezoelectric actuator. In this case study, the unbalanced SSA circuit does not affect the vibration control at the resonant frequency in the closed-loop system. The vibration of the piezoelectric system at the resonant frequency is attenuated by 16 dB in both the balanced and the unbalanced SSA circuit conditions.