Here are the circuit schematics, BOM, as well as the PCB layout. The filter response graph is also shown. Keep in mind that the graph is more of a perceptual one than actual.
The circuit is loosely based on the many vintage circuits before it, with a few improvements.
The input buffer/gain stage is designed to have low output impedance. This is important for the filter stages that follow. This stage is also designed to give high gain and maximum output signal level, since the filters are of passive type so will lose some signal.
(This amplifier stage took me the most time to design. I tried out many topologies and parameters. I think I found the best balance between simplicity, stability and performance. Unlike using op-amp, designing amplifier with transistors is an art of compromise.)
The use of emitter follower as rectifier is my original idea. (Q3, 5 and 7) Combined with the bias point set (by R8 and 9 and so on) right below the point the LED driver turns on makes this color organ very sensitive to the lower volume of audio input, while eliminating the diodes typically used here.
All resistors are 1/8W (or higher) carbon film type, 5% precision. Small capacitors are film type, and 0.22uF and above are electrolytic type having voltage rating of 16V or higher.
This type of analog circuits tend to be picky about the part values, so it's best not to change out resistor values, etc. unless you know what you are doing.
Resister and capacitor types are not very critical, so just use any type you might have. Using ceramic capacitors instead of film for example, is fine.
I used MPS2222A transistor, which can be substituted by number of general purpose transistors of similar specs. The ones I tested are 2N4400, 2N4401, and 2N3904.
Q1 is more critical than other transistors in this circuit. The biasing is adjusted for transistors having the hfe around 200. If you use different transistor, you might want to check the voltage at Q1 collector - the voltage here should be between 4.5 to 6V when 12V supply is applied. Adjust R5 or try different transistors for Q1 if it's too high or low.
PCB layout is provided as PDF for home brew PCB makers. It's a single layer design, so it should be easy to make your own.
Kits and PCBs
Kits and PCBs of this project are available at my website.
There are 8 transistors, and many resistors, capacitors and LEDs, but the assembly is very straightforward as they are all familier through hole parts (and no ICs). In a way, Color Organ Triple Deluxe II is built like the circuits from the 70's. If you are like me, you will appreciate the modern-vintage feel of all discrete component design.
I recommend soldering the lower profile parts, first, then move on to taller and taller parts. I arranged the BOM in the order of soldering below:
Notes on Solder Resin/Flux
Some solder resin/flux is electrically conductive. (resin or flux is inside solder wire to help solder to adhere to the joints) Some parts of Color Organ Triple Deluxe II are very sensitive to even a tiny amount of electrical leakage caused by soldering resin/flux. If the LEDs on Color Organ Triple Deluxe II stays lit without any sound signal coming in, you need to clean the PCB to remove the resin/flux.
"No Clean" type flux cause no problems (as the name implies), but more typical resin type flux can cause good amount of leakage, and cleaning might be required.
You can use an acid brush or an old toothbrush immersed in rubbing alcohol to scrub the back of the PCB. Rinse out the brush, wet with alcohol again and scrub another round or two until all the resin residue is gone. Make sure to dry the PCB completely before connecting to the power supply.
Color Organ Triple Deluxe II is designed to run by 12V DC power supply. The circuit works pretty ok with 9V power, though. However 9V battery is not recommended as a power source because of the relatively high current draw (about 25mA at idol).
It's best to connect to a regulated 12V DC power supply. Be careful if you want to use a typical wall wart - they can output much higher voltage than they are rated - sometimes as high as 18V from a 12V one. Color Organ Triple Deluxe II can operate safely from up to about 15V power. (If you want to use non-regulated AC adaptor, try a 9V rated one - they typically produce around 13V).
Audio source can be any "line level" output from audio equipment, or headphone output from computer sound cards and iPod/MP3 players. If you want to listen to the music while using Color Organ Triple Deluxe II, you might need a splitter cable.
Connect Color Organ Triple Deluxe II to your audio source of choice, and give it a play. I found music with good amount of beats to give best results. Adjust the potentiometer (sensitivity level) according to the sound level.
The LEDs react to the sound volume in a pretty linear manner that it feels like the Color Organ is translating sound into light.
The light out of the LEDs are blinding bright. You can use Color Organ Triple Deluxe II as a wall wash - project the light towards walls or ceiling and dim the lights in the room.
You will discover a new joy of listing to music.