A vernier drive is an essential item here as the tuning is very sharp.I made the dial from white styrene.Use your imagination to make a dial of your own.

• 在音量控制器边的四个硅二极管是我用来抑制杂声的一个办法，当循环泵打开和关闭的时候，耳机里总会发出大的杂声。