VU LED indicator is simpler and smaller than their analog, and very common in audio equipment. This version is based on National Semiconductor IC, and using the logarithmic version. Each LED operates with a 3dB difference from before, and the jumper is provided to allow dot or bar mode.
The circuit is completely conventional, and is based on application notes from National Semiconductor. The circuit is shown in the picture below and you can view it with a single IC and some discrete components. DC to the LED is almost filtered - C1 are included to ensure that the IC does not oscillate, and is not a filter cap.
This allows a higher LED current with lower dissipation than is the case if the DC is fully refined, and full smoothing would also require much larger capacitors. This will increase the size and cost of the project - especially important if you want to use in larger quantities that may occur with a mixer or analyzer.It could not be simpler. At the maximum level that you want to operate the equipment (as shown on the audio millivoltmeter or an oscilloscope with a signal applied), adjust VR1 so that the signal light to all the green LED (L1 is the most sensitive, and L10 showed the maximum level, so L1 to L8 should be lit ). If the input directly from the speaker output, an additional series resistor should be used in terminal "Aud" input to reduce the level. This can be determined by calculation (I leave it to you) or by experiment. As a guide, for 50W amplifier, an external resistance should be about 47k ohms.If you calibrate the meter for the power amplifier, set the output to a level below clipping. Adjust the level control until the LED turns on. In this way, if (L10) LED bulbs last when you're listening to music, you'll know that you are very close to clipping, and volume should be reduced.