Retro Color Organ

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2025-03-05 | By Sara McCaslin

License: See Original Project Capacitors Diodes Resistors Transistors LEDs / Discrete / Modules

A color organ, also known as a light organ, visually represents sound by synchronizing ‎changing colors with the sound. It translates sound (or music) into visual effects. Basic ‎electronic circuits can be built that filter audio frequencies to determine which lights should ‎be activated. Specific colors and/or light patterns can be assigned to different tones or ‎ranges. The image below shows some color organs from the 1970s.‎

Copy of Figure-1

A retro color organ. Source.‎

In this project, a combination of high-pass, low-pass, and bandpass capacitive filters light ‎up different LEDs based on the frequency of the sound. The approach combines the light ‎drivers with the filter stage to simplify the design and reduce the parts list, making it ‎inexpensive to implement. This project is based on LED Color Organ Triple Deluxe: 4 Steps ‎‎(with Pictures)—Instructables. ‎

What is a Color Organ

Color organs have been around for many years. They create highly dynamic, synchronized ‎light shows that enhance the sensory experience of music and sounds. These devices can ‎be standalone or integrated into larger systems, such as stage lighting or multimedia ‎installations. In the 1960s and 1970s, electronic color organs became essential to many ‎music performances, adding dimension to the music being heard.‎

Modern color organs can involve complex interactions between code and hardware, but ‎simpler ones can be built with standard circuitry components, a source for the audio, and a ‎‎9V battery.‎

Parts List

There are a total of 32 parts in the BOM (Bill of Materials) as listed below:‎

Resistors:‎
- ‎3x 100 ohm resistors‎
- 1x 180 ohm resistors‎
- ‎1x 270 ohm resistors‎
- ‎2x 1k ohm resistors‎
- 4x 2.2k ohm resistors‎
- ‎2x 10k ohm resistors‎
Capacitors
- ‎1x 0.047 uF capacitor‎
- ‎1x 0.01 uF capacitor‎
- ‎1x 0.47 uF capacitor‎
- ‎1x 1 uF capacitor‎
- ‎1x 10 uF capacitor‎
Transistors
- ‎1x 2N2222A, 2N3904 (or equivalent NPN transistor)‎
- 3x 2N2907A, 2N3906 (or equivalent PNP transistor)‎
Diodes: 1x 1N4148 diode‎
LEDs: 6x LED (2x Red, 2x Green, 2x Blue)‎
Breadboard with assorted jumper wires
Wirecutters
Audio: stereo headphone cable
Power: 9V battery and connector/holder

If you need help identifying the resistors, try DigiKey's 4 Band Resistor Color Code ‎Calculator. They also have an RC and RL Passive Filter Calculator. ‎

You can find the circuit diagram for this project below. The first filter is the high-pass filter, ‎the second is the band-pass filter, and the third is the low-pass filter. Note that diode D1 is ‎‎1N4148 or equivalent, transistor Q1 is 2N2222A (or equivalent), and transistors Q2 ‎through Q4 are all 2N2907A (or equivalent). Transistors Q2, Q3, and Q4 serve to amplify ‎and switch the LEDs on or off based on the signal from their respective filters.‎

Copy of Figure-2

Circuit diagram for the simple color organ.‎

How This Retro Color Organ Works

The color organ works in a very straightforward manner: the audio signal is boosted by an ‎amplifier and then passes through three filters. Each filter connects to a transistor and ‎LEDs. Here are the approximate frequency cutoffs for the filters in the project: ‎

Low: less than 72.34 Hz
Mid: between 72.34 Hz and 1.54 kHz
High: greater than 1.54 kHz

Notice that the formulas for these filters are related to f_c, the cutoff frequency, and to R and ‎C (Resistance and Capacitance, respectively). In short, f_c = 1 / (2𝛑RC), which means that ‎you can change the cutoff by modifying R and/or C. Below, you can see the high-pass ‎filter's resistance and capacitance, and the resulting cutoff frequency.

Copy of Figure-3

High pass filter. Source.

Copy of Figure-4

Low pass filter. Source.‎

Next, the circuit passes through a band-pass filter, Filter 2. Filter 2 combines Filter 1 and ‎Filter 3 in series. Only the middle-range frequencies of the audio are allowed to pass ‎through and activate the green LEDs. Finally, Filter 3 only allows the low frequencies to pass ‎through and activate the red LEDs. ‎

How To Build the Circuit

Step 1‎

Verify that you have all the needed parts, including wire cutters and a breadboard. The ‎recommended setup for the power is shown below, but the battery should not be connected ‎until the circuit is complete.‎

Copy of Figure-5

Breadboard setup with power.‎

Step 2‎

Let’s move on to the audio input for the circuit. The audio signal comes from a set of basic ‎stereo headphones. When you cut the headphone cord and strip it, you see three wires: two ‎carry the audio signal (left and right), and one connects to the ground. The three wires in ‎this project are shown in the previous circuit diagram, where the gold wire connects to ‎ground. The input from the headphones is connected to the circuit with two 100Ω resistors ‎all in parallel.

Copy of Figure-6

Individual wires in a stereo headphone line.‎

Step 3

Now assemble the far left of the circuit, shown below. The diode D1 is 1N4148 or ‎equivalent, and transistor Q1 is 2N2222A (or equivalent). The current from this part of the ‎circuit flows to Filters 1, 2, and 3.‎

Copy of Figure-7

The initial portion of the circuit.‎

Step 4

The next step involves assembling the filter and LED circuits. Note that you can set up the ‎LEDs in a different order; just make sure they still have the appropriate resistor after the ‎LED. Also, note that transistors Q2 through Q4 are all 2N2907A (or equivalent).‎

Copy of Figure-8

Detail of the filter and LED portion of the circuit.‎

Modifications

This basic circuit can be modified in many ways. For example, you can increase or decrease ‎the number of groups into which the frequencies are divided. You can also change the LED ‎colors and the number of LEDs and modify the individual filters by adjusting the resistance ‎and/or the capacitance. In addition, a more permanent circuit than a breadboard can be ‎assembled and placed in a wooden enclosure to complete that vintage feel. ‎

Conclusion

Color organs are still fun to build, whether simple designs, as shown or more complex ‎designs using addressable LEDs. This project demonstrates a simple yet effective ‎approach to building a color organ: a combination of high-pass, low-pass, and band-pass ‎filters translates audio frequencies into a dynamic light show. This retro project provides a ‎fun and engaging way to experience music and offers a valuable learning opportunity in ‎electronics and circuit design—with no expensive, unusual components needed.