Led, help

[shimniok]

Sorry if this was mentioned and I missed it.

Seems to me that with the wide possible variance in voltage at the speaker terminals you'd be miles ahead connecting the LEDs to a tape out / preamp out / whatever line level output on the stereo. That way voltage stays constant despite changing volume. And you're dealing with less voltage...

Michael

 

[audioguru]

Sorry if this was mentioned and I missed it.

Seems to me that with the wide possible variance in voltage at the speaker terminals you'd be miles ahead connecting the LEDs to a tape out / preamp out / whatever line level output on the stereo. That way voltage stays constant despite changing volume. And you're dealing with less voltage...

Michael

But a line level output does not provide enough current to light LEDs and the voltage is probably much too low.

Line level output has exactly the same variance in levels as the speakers output. The dynamic range of music is at least 60dB which is 1,000 times. So a peak of 40V at the speakers drops to only 40mV on the not loud parts. A peak of 400mV at the line level output drops to only 400uV.
A white or blue LED needs about 3.2V to barely light.

 

[shimniok]

But a line level output does not provide enough current to light LEDs and the voltage is probably much too low.

Ah... right... that would be a problem then I could swear line level voltage is more on the order of 2-3V.

Line level output has exactly the same variance in levels as the speakers output. The dynamic range of music is at least 60dB which is 1,000 times. So a peak of 40V at the speakers drops to only 40mV on the not loud parts. A peak of 400mV at the line level output drops to only 400uV.
A white or blue LED needs about 3.2V to barely light.

Right, agree about *signal* variance. But my point was -- the p-p voltage at the speaker terminals increases as you turn up the volume. Not so with line level. The reason I brought this up...

I assumed the goal is to have the flashy light effect happen at most if not all volume levels. If so, and if one designs for a mid level volume, then I would think the lights would stay lit most of the time at max volume and hardly at all at min volume... but maybe this is what the OP wanted.

I may be making too many assumptions and we all know what they say about assuming

Michael

 

[audioguru]

Instead of just flashing brightly during the loudest peaks of music, I think an LED would look better if it showed the levels of the signal with varying brightness levels which would happen if the voltage feeding the LED and its current-limiting resistor is high enough.

 

[sheldonstv]

you could try this circuit but you would need to either feed it from the preamplifier section of yr power amp or if using it direct from the loudspeakers it is possible to attenuate the signal so you wont have to worry about overdriving the circuit...also if u add the line amp as shown(nothing to stop you adding an electret mike(plus components to provide the ecm with a supply(a mega xpensive resistor.10k or so plus an xtra capacitor,4.7mf or whatever you have to hand)and you have a complete stand alone unit with no connection needed to yr amp