A power conversion circuit is provided. A variable strength controller is provided that has a feedback terminal, at least one p-terminal, and at least one n-terminal. Each switch circuit includes a channel unit and two switches. The hollow pipe connects to a cover that contains reciprocal ridges and grooves that create a strong hold and ease of assembly of the electronic percussion instrument stand system. The method and apparatus allow the significant improvement of the etching rate while maintaining the accuracy of etching.