'Signal detect' LED for a small audio amp?

[HankMcSpank]

For no other reason than visual information/effect (not worried too much about impact on fidelity), I'd really like to add a LED to a circuit such as this...

http://runoffgroove.com/fetzer-ruby.png

This will help identifying which channels have signal (there's going to be up to eight amp channels)

I don't need any degree of accuracy here - just the LED to light up when a signal above a certain threshold is detected somewhere along the signal path (rather than have it flash on/off abruptly, some form of fade in/out would be brilliant!)

Is there any appropriate place (or extra bit of circuitry needed) to add an LED in? (space is going to be tight, so component count associated with adding in the LED is important - ie less is more here!)

Many thanks.

[djoffe]

on the speaker side of the output cap, place an LED in series with 200 Ohms. The little amp will have to be cranking a bit, but whenever the AC out is greater than about 1.7 Volts (depending on LED), the LED should start to light. There are more sensitive options, but they take some more components.