Much more than just a signal presence indicator, this small VU meter displays the following levels:
-20 dB, -6 dB, 0 dB, +6 dB. Its role is primarily focused on source calibration, for example, to adjust the gain of a microphone preamp. We can only lament the loss of legendary circuits like the TFK257, TFK267, UAA180, LM3915, and LM3916. The KA2284 remains available on the Asian market, but it is becoming obsolete. The circuit I propose uses components available from your usual supplier.

The incoming signal is converted by a thresholdless active rectifier around the TL071. This simplification is often found in mixers like Mackie, Allen & Heath, etc. The R-Attack, Ct, Rt network establishes the time constant. I've analyzed quite a few schematics over the years, and there are many variations. Some lean more towards the "PEAK" or "AVERAGE" effect.
This rectified component is then sent to comparators based on the two LM393s. A resistive bridge sets the various thresholds at the E+ inputs. The LM393 has open-collector outputs that are high at rest. As soon as E- crosses a threshold, the output goes to 0V, which turns on the LED. This eliminates the need for a separate LED driver transistor. An LED with its current-limiting resistor can be connected directly. The models I use are 10mA with 330 ohm resistors {5V-1.7V / 10mA}. Less power can be consumed with 2mA LEDs and 1.5kΩ resistors.

The setup is simple:
Inject a 1 kHz, 775 mV signal and turn the adjustable knob until the 0 dB LED lights up.
Increase the voltage to 1.55 V and the red LED (+6 dB) should light up.
Decrease it to 77.5 mV and the green LED (-20 dB) should light up.

Where else can you place this module?
Its 47 kΩ input impedance won't interfere with preamp outputs.
Some mixers only have VU meters on the master output. The pre and post aux sends don't have them, so this is a good opportunity to add one.
Another tip: place a selector switch at the VU input to perform multi-point monitoring. This allows you to track an audio signal chain.