Peak Indicator Circuit

How to build a peak indicator circuit . Each time where the level of signal exceeds the level + 4dB, turns on led D1. It is useful in each channel of console of sound, in final amplifiers or in that other application, to we needed. With the prices of circuit, the indicate begins with levels above + 4 dB (1.25V rms). For adaptation in different levels of signal, we can use a trimmer, before capacitor C1.
Parts:

R1 = 10K
R2 = 1.2K
R3 = 220K
R4 = 4.7K
R5 = 4.7K
C1 = 47uF-25V
C2 = 2.2uF-25V
Q1 = BC550C
Q2 = BC550C
D1 = Red LED

Notes:

It can be assembled on a general purpose PCB.
It can be powered from a 12V-15V regulated power supply.