Making Refinements to the Old Project

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

The Problems

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.

The Solutions

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.

Step 2: Circuit

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.

BOM

3x 47 ohm - R4,17,20
6x 150 ohm - R10,15,16,16b,21,21b
2x 270 ohm - R11,11b
1x 470 ohm - R6
2x 1k ohm - R1,2
2x 4.7k ohm - R7,12
4x 10k ohm - R3,9,14,19
3x 270k ohm - R8,13,18
1x 1.2M ohm - R5
1x 10k ohm potentiometer - VR1
1x 4.7nF (0.0047uF) - C9
2x 22nF (0.022uF) - C6,7
1x 0.22uF EC - C3
1x 1uF EC - C4
3x 4.7uF EC - C5,8,10
1x 10 uF EC 16V or higher - C2
1x 47uF EC 16V or higher - C1
8x MPS2222A or Equivalent - Q1-8
6x Red LED (super bright type recommended) - D1-6
6x Green LED (super bright type recommended) - D7-12
6x Blue LED (super bright type recommended) - D13-18
1x 3.5mm Stereo Jack - CN1
1x DC Power Jack

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.

Parts Substitutions

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
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.

Step 3: Assembly

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:

Soldering Order

Resistors (bend the leads) (reference on color code)
- 3x 47 ohm (yellow, violet, black, gold) - R4,17,20
- 6x 150 ohm (brown, green, brown, gold) - R10,15,16,16b,21,21b
- 2x 270 ohm (red, violet, brown, gold) - R11,11b
- 1x 470 ohm (yellow, violet, brown, gold) - R6
- 2x 1k ohm (brown, black, red, gold) - R1,2
- 2x 4.7k ohm (yellow, violet, red, gold) - R7,12
- 4x 10k ohm (brown, black, orange, gold) - R3,9,14,19
- 3x 270k ohm (red, violet, yellow, gold) - R8,13,18
- 1x 1.2M ohm (brown, red, green, gold) - R5
1x 3.5mm Stereo Jack - CN1
Capacitors (watch the polarity of electrolytic capacitors - long leads go into the holes with "+" sign on the PCB)
- 1x 4.7nF (0.0047uF) Film Capacitor - C9
- 2x 22nF (0.022uF) Film Capacitor - C6,7
- 1x 0.22uF Electrolytic Capacitor* - C3
- 1x 1uF Electrolytic Capacitor* - C4
- 3x 4.7uF Electrolytic Capacitor* - C5,8,10
- 1x 10 uF Electrolytic Capacitor* - C2
- 1x 47uF Electrolytic Capacitor* - C1
Transistors (polarity - make sure to orient them to the shape printed on the PCB)
- 8x MPS2222A or Equivalent - Q1-8
LEDs (polarity - make sure to orient them to the shape printed on the PCB)
- 6x Red LED - D1-6
- 6x Green LED - D7-12
- 6x Blue LED - D13-18
1x DC Power Jack
1x 10k (50k) ohm potentiometer - VR1

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.

Step 4: Use

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 idle).

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.