I put together the Color Organ Triple Deluxe over a year ago. It was a bare minimum version of color organ circuit using LEDs instead of incandescent lamps that traditional color organs use.
The circuit worked pretty well, considering the simplicity of the circuit. However I just kept feeling like this project deserves further refinements. So I went back to the drawing board (or breadboard) and took a hard look at the circuit...
The result? Please take a look at the video.
Step 1: The Problems & The Solutions
There were a few problems. The transistors in the circuit was biased in the way that it was supply voltage dependent, as well as device dependent - in other words, if the voltage was too high or too low, or the transistors had a bit of different characteristics, the circuit did not perform well.
The filter performance was also a bit poor - the separation between the frequency bands were not so great.
First, I changed the initial gain stage from single transistor design to two transistor design. It's a basic class-A common emitter amplifier followed by an emitter follower. They are direct coupled for optimum performance, as well as reduced part count (always important for me to design circuits with the least number of parts). Adding the emitter follower stage allowed the low output impedance needed for the filters to perform well. The biasing circuit was also revised to be less device and voltage dependent.
Second, the filters were refined to have better separations. Input and output impedance to the filters are better matched to achieve better efficiency as well.
Third, the LED driver circuits were given another transistor. Actually, in the original design, the output buffer and the LED driver was done by the same transistors. Now the filter outputs are buffered by emitter followers, then the filtered audio waves are rectified before going into the LED drivers.
Those changes made a huge difference. And I tweaked the component values obsessively to get the best performance. Sensitivity adjustment control is also added.
There are many additional parts compared to the earlier version, but the result is totally worth it. The LEDs now respond to music very, very nicely.