This is a simple Audio Millivoltmeter Circuit Diagram . An audio millivoltmeter that's easy to build, accurate and extends to beyond 100kHz. This Audio Millivoltmeter circuit has a flat response from 8Hz to 50 kHz at -3 db on tbe 10-mV range. The upper limit remains the same on tbe less sensitive ranges, but the lower frequency limit covers under 1 Hz. An Audio Millivoltmeter Circuit Diagram