Need thoughts on gimic tuner

[Jabulani Jonny]

Okay, this is going to sound strange.  My long-time (12 years) gigging buddy and bandmate is moving away.  I want to make him a one of a kind "tuner".  Basically I want a single LED that lights up when it receives any audio signal.  Preferably brighter with stronger signal and fading as the signal from the guitar dies.  Does that make sense?  Seems like it would be a very easy circuit to come up with, but I'll need someone more versed than I to draw it up.  Anybody feel like helping me out?  I would greatly appreciate it.  Yeah, so if you're wondering, he'd always be "in tune".   

Thanks!

[kgull]

Sounds like you want an envelope follower, this one looks pretty simple:


Edit: This one actually looks even simpler:

[Jabulani Jonny]

Yeah, that second one looks pretty easy.  Let me see if I have an LM386 sitting around and should be able to test it out. 

[Jabulani Jonny]

Well I don't have the LM386 on hand unfortunately.  I would think that just about any opamp would work, but it looks like the 386 has a different pinout than others. 

[flanagan0718]

Well I don't have the LM386 on hand unfortunately.  I would think that just about any opamp would work, but it looks like the 386 has a different pinout than others.

If you need one I've got a couple I could send you.

[midwayfair]

Look at the afterlife and leave out the LDR.

You don't need an LM386, any dual op amp will work.