Here is a little project I have been working on, to control brightness level of a color organ through a PWM driver via a smoothed low pass freq to voltage RC filter. The results were nice, I have built and tested the circuit on my discrete PWM driver. I could not smoothen the waveform any more without introducing lag/delay into the system.

This is a ~120Hz low pass RC filter, mainly aimed for drum and bass freq. Very responsive, roburst

The circuit works as follow: Q1 + Q2 are used to amplify, clipping and converting the low mV input signal to almost at fullwave rectification for ease of smothen it out by Q3. The smoothened signal can then be fed to a PWM to drive LEDs or whatever

I dont understand why many color organ circuits found on the net use large caps and low resistors value!? What a waste of power!

As always, suggestions/comments are most appreciated