Color Organ Design

[aep9690]

I got the idea to make a color organ recently.  I am done with the design and simulation of it and am going to go into PCB design now.  Before I do this I would like to get some feedback on the design to see if I made any mistakes.  I attached the schematic, the way the circuit works is it takes the signal from the headphone jack and amplifies it by 10.  It is then filtered by the three active bandpass filters which is then used to drive the darlingtons on the output.
A few notes:
1.)  This is not very efficient, I know, I plan on implementing an LED driver board later.
2.)  I am using Darlingtons because I want to use this with 1W RGB LEDs.

[Astroplio]

Are you going to use potentiometers or resistors for the irregular resistor values?  (R4,R8,R14 etc)

George

[Astroplio]

The reason I am asking this is because you will probably need to do some tuning to get a more pleasing visual effect.

I have breadboarded a color organ in the past and I found that the low frequencies were dimming faintly the Red LEDs, the mid-range frequencies kept lit the Green LEDs most of the time and high frequencies were blinking very fast the Blue LEDs.
So I had to play with the RC values a bit.

I am not sure how exactly I went on about this, but I think I used a pot to find the suitable resistance and then replaced it with the equivalent series resistance of a resistor network to set the right value. I also changed a capacitor to a smaller value.

Now how I went on about driving the LEDs I don't really remember at all... It is possible that I have added a capacitor between base of Transistor and GND for a dim effect.

But yeah, surely this color organ circuit is not so much about getting the frequency ranges right but creating something aesthetically pleasing which of course is subjective... It is up to you to tune the behavior of your organ.

George

[aep9690]

I thought about using pots but I was pretty sure that the filters were okay.  However if you think its a good idea to include those I will probably through some single turn 20k pots in place of R4, R8, and R14.  What were you saying about including a cap between the base and ground?

[David_AVD]

Most colour organs are finicky beasts and it's common to have to adjust the separate channels to suit the music style and signal source.

Back in the late 70's - early 80's, Pulsar (in the UK) made a 3 channel one that had no controls.  It had AGC, etc and was an amazing piece of kit.  Just plug in the audio source and lamps and you're off !

[aep9690]

I'll have to give that a google, in the mean time I will add some single turn pots to dial it in.