A plurality of main amplifiers amplifies input audio signals with an adjustable gain. The apparatus includes a bath container for containing a bath solution, an anode provided in the bath container, a cathode ring for supporting a wafer in the bath container and a current source electrically connected to the anode and the cathode ring. Methods for using and making the ball hitting practice are also provided. The spring biases the detent element into the recess and against the ramp to generate an axial force against the ramp. The server system computes a deadline for each job to be the arrival time of the job request plus the product of the processing time and the proposed stretch value. The section of the housing in which the stent is held during the coating procedure is detachable from the housing base.