Origional Article Created in 2006.
Back in the 1970's these Devices were popular for use in homes and the colored bulbs were typically place in a box with a sheet of "rippled/bubbled" Plastic in front to break up the light patterns. Some units gave very impressive light patterns.
Using an LM324, this circuit has 3 Active Filters for the Low, Medium and High Frequencies. These Active Filters give a Much better seperation beween the various frequency ranges than the simple Passive Filters as used on many other Color Organs.
Each of these 3 filters are now 2 Octaves Apart, at 250, 750 and 2,250 Hz.
Setting it up:
I recommend Setting the Master Level to about a 1/4 or 1/2 on position.
The 3 Frequency Trimpots are initally used to set the 3 filters to equal ranges so the lights all flash in about equil amounts of time to your music. (These can also be Standard Pots if wanted.)
The Master control, is usually a Standard Potentiometer, and is than used to set for various volume levels. (I just used a Trimpot on my proto for testing purposes.)
Proper Rated FUSES are Highly Recommended. Except for the On-Board fuse that protects the IC Circuit, The fuses I recommend for protecting the Mosfets should be "Automotive Types", with a voltage rating of 32 Volts. and at an appropriate Current for the bulbs you use.
"T1" is Mainly for Isolation and some signal boost. It can be almost any small audio transformer, used in reverse. The one stated here is reasonably priced and fits the board nicely. "T1" is Essential to "Isolate the audio output" from ground on Non-Grounded Speaker Outputs.
Audio Input, Power Protection "RX", As Shown on the Circuit Board is a series connected 12 or 28 Volt Lamp. This Lamp Creates a CURRENT LIMIT to protect T1 from Excessive Power.
Heatsinks May be required on the Mosfets, Depending on you load Currents. The STP75NF75 Mosfet I use has a Good Current Rating With a Proper Heatsink, it is Probably suitable for loads up to 30 amps or so.
Be Aware that the "Mostfet Heat Tabs" are at a Varying Voltage Potential. SO DO NOT GROUND any of these Heatsinks.
Also Consider that if you have 3 Channels, each drawing 30 Amps at times, That means you could be drawing 90 Amps in total. That is a LOT OF CURRENT.
The Loads: Although I Prefer Standard Filament Bulbs for the BEST DISPLAY of Light, You may also use LED's with there appropriate Series Resistors. But LED's are usually either "FULL On or Off", with Little change in Brightness.
Other Devices such as the 12 volt Colored Neon lights may also work. I Don't have them to give that a try.
An Etched and Drilled PCB or a Complete Kit may be available for this Color Organ.
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Revised Color Organ Schematic for N-Mosfet
Color Organ PCB for N-Mosfet
Revised Color Organ Picture Overlay for N-Mosfet.
Revised Frequency Response Graph
I assume all the info in this article to be correct, But I assume NO Liability
for Errors or Injury in making this or any of my projects.
BUILD THEM and USE THEM AT YOUR OWN RISK.
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