LED powered by audio signal

Thread Starter

FSTOP

Joined Jan 26, 2009
6
HI. I am trying to find an LED that can be powered by just the audio power of a typical stereo amp's single-channel output. NO battery or other voltage input, just the audio signal from the amp to the speaker. Does not need to be particularly bright, blink, or do anything but light up with the audio power. I am assuming i need something that will run on 10mV or less? I cannot seem to find anything like this searching online. I am sure such an LED exists, as i have bought VU meters that run on just the audio signal with no power. But i am only needing a single LED to light up with audio power. ANY IDEAS or know where i can find such a product??
In case you are wondering the purpose, i am trying to back-light an epoxy mold for a logo that will light up when in use on a custom speaker system...

THANKS FOR ANY HELP YOU CAN PROVIDE!!!!
 

Thread Starter

FSTOP

Joined Jan 26, 2009
6
I don't have a way to test at the moment. Even cranking a high-power amp up wouldn't get actual voltage would it? I am generally using lower-wattage T-amps as well. Would like to get some amount of light without continuous high dB levels :). Inform me, if you can, as i am no electronics expert--That's why i am here. Is there a place to find low-level LED's?
 

beenthere

Joined Apr 20, 2004
15,819
LED's take a certain amount of voltage to push electrons across the internal structure. That energy is what lets those electrons emit the photons that we see as the characteristic light. You might find an LED with a forward voltage a bit less than 1.5 volts, but never as low as 10 mv.

VU's are sensitive voltmeters. Low voltage and current.

You may have to resort to a battery operated circuit to give the results you need.
 

Externet

Joined Nov 29, 2005
2,198
Connect two red LEDs in counterparallel and to a speaker output from an amplifier.
They will light up unless the amplifier is too weak as from a portable radio.

Exceeding volume level can damage them.

The newer the technology of the leds be (efficiency), the brighter they will shine compared with older ones; but all will light up at the same volume level.
 

Audioguru

Joined Dec 20, 2007
11,248
Sound from speech and music has very short duration peaks. An LED would instantly light then turn off on those peaks so quickly that your vision's slow response to brightness will not see the blips of light. The circuit needs a "peak detector" to hold the LED turned on for a moment that is long enough to be seen. The LM3915 bar-graph IC's datasheet has some peak detector circuits.

If the max power to a speaker is 60W then the voltage at the speaker is 21.9V RMS if the speaker is 8 ohms. A low sound level from the speaker is caused by a signal that is 0.22V RMS.
 
Top