Whirring noise from the PreCHAMP

摘要

I am having trouble trying to interface a mono dynamic microphone (250Ω impedance) to the sound card of my computer. I have found an old Jaycar "Pre-Champ" kit, Cat KC5166 (now apparently discontinued), based on your article in the July 1994 issue. It amplifies just fine but there is a continuous whirring sound in the background (only when the mic cable is plugged in). I suspect it may be rapid motor boating.