Sound-sensitive LED setup for speaker cab or amp

Ch Ra

Member
Messages
125
Hello, I'm thinking of modding my speaker cab or amp with LED strips that will flash with the intensity of the sound. Yes it's silly I know, but in a dark room, it could look cool. I'm thinking of driving an LED strip with the amp output itself, but I'm a little concerned that: (1) I could blow the LEDs or (2) create a weird impedance mismatch with the speaker cab.

For instance, would I need to use a high power resistor before the LEDs (like a 25W resistor for an 18 Watt amp)?

If I use the extension cab output from my amp to drive the LEDs, would the amp "see" a different impedance than it would without the LEDs?

If I split the signal at the Cab, would the impedance change if the LEDs are switched off?

Curious to hear if anyone else has tried this and if so what your experience has been.
 

Jeff Gehring

Gold Supporting Member
Messages
6,201
Don't drive the LEDs directly from the amp, the amp needs to be completely isolated from the LED thing. The output of the amp to the LED driver should be a capacitively isolated signal, with a series resistance also. The LED driver should accept this quasi line level output from the amp to do its thing. There are lots of color organ schematics and ideas floating around the web.
 

Ch Ra

Member
Messages
125
@xtian That's exactly what I was imagining. In fact, I even imagined myself doing those awesome riffs (in reality I would sound a lot worse). But yeah I set up my amp in a head cab with a plexiglass front so you can see the amp head guts. Some lights in there would be great.

Does your LED setup actually respond to the sounds or do the lights move at random? At times it looked like they were responding to your volume transients, but then the color changes seemed random.
 

xtian

Gold Supporting Member
Messages
2,444
Does your LED setup actually respond to the sounds or do the lights move at random? At times it looked like they were responding to your volume transients, but then the color changes seemed random.
Thx, mate. The RGB controller has a microphone, so yes, it does actually respond to ambient sound. The sequence of colors is preprogrammed. And it will change by itself if there is no sound to drive it. It's an incredibly cheap solution, so I was happy to accept it's behavior as-is.
 

Ch Ra

Member
Messages
125
@PremiumPlus That's cool. Did you use the circuit in the datasheet? I've seen some pretty simple VU meter schematics.

I'm thinking of trying this with a little microphone for the audio in. Would that work or would the mic input just saturate when the music is loud?
 

xtian

Gold Supporting Member
Messages
2,444
Yes, the typical electret mics in those projects gets swamped at band volume. But it would still respond, I think. Look here for more inspiration:

 

PremiumPlus

Member
Messages
1,106
It hooks up in parallel with your speaker outputs, no mic. Sensitivity is adjustable, and the schematic that they supply is what I used to build a 2 channel 10 LED per channel output meter. Each driver chip handles ten LEDs so use two for stereo. You can also cascade two chips (or more, I think) and run 20 LEDs for your display if you like. It's a really sweet circuit.
 




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