60-dB LED VU Meter

Most of the analogue audio media, including radio broadcasting, stick within 60 dB dynamic boundaries. This VU Meter was designed to be used as a desktop instrument with home audio appliances, so it has its own power supply. Driven by an AC musical signal taken directly from low impedance loudspeaker connectors, i.e. in parallel with loudspeakers, and having linear frequency response, it covers 60 dB dynamic range in 3 dB steps using 20 LEDs in a bargraph. Low component count and simplicity enable the circuit to be housed in a small box or behind a transparent shield like a small acrylic desktop photo holder.

Due to a scaling error, the lower part of the circuit diagram is not visible. Components C5 and R7 should be connected to ground. The connections for S1 and S3 are on 3-way headers. The pole connection is at pin 3, not 2 as expected. Junction D21-C6-IC3 is erroneously labelled ‘+5V’. A suggested label is ‘V+’.