led flashing while playing

[Dimitree]

hi everyone
I'd like to build a little circuit with a led that lights on when playing. I know it would be easy to do just using an envelope follower, but that would use much parts and I don't need that accurate.
so I draw this:



I put a trimpot in order to set the "sensitivity". I don't have the chance to breaboard it, so I was wondering if it would work before making a pcb. Is there any downside? I was a bit uncertain about current drawing. I would drive this circuit after a splitted/buffered signal.
Voltage would be +15V DC or +18V DC.

suggestions?
thanks

[nomorebetts]

Unfortunately my work's internet filter blocked your image...

But have you seen this:
http://www.diystompboxes.com/smfforum/index.php?topic=82843.msg687720#msg687720

Might be worth a look.   

[PRR]

> so I draw this:


Should work.

The input impedance is a very-low 1K for small signals and some higher value when overloaded; this may load-down or distort whatever is driving it.

The opamp is able to drive an LED directly.

The 33nFd-10K network passes transients, but is liable to charge-pump to an "off" display giving only very short blips of light. If you want a peak-hold function, so that "sound" is indicated for a short time after sound stops, you do need an RC network, but not like this.

You can implement half-wave indication with an offset (so very-small sound/hiss is not displayed) with a simpler plan:



> I don't have the chance to breaboard it

You need to breadboard these things. If you "must" go right to PCB, leave a lot of extra pads so you can tinker the variations.

> my work's internet filter blocked your image...

I believe his hosting service postimage.org refuses hot-links. I re-hosted Dimetree's at imgur.com; is that working for you?

[Gurner]

whilst using a 'threshold' (gate) is beneficial, unfortunately such a circuit has a binary outcome ...ie the led(s) wll be is either full on or completely off - & nothing in between    ...I'd reckon that most guitarists would likely want a sound to light circuit where the light intensity is proportional to the strum/string strength (ie more resolution for the led) ...of course it can be done in analogue...but it starts getting component heavy to get a decent LED response   .....if you want to keep the parts count low....PIC!

[Dimitree]

many thanks

where do you suggest I should place this? obviously after a splitted signal, but, do I need a buffer before this circuit, or using after the splitted signal is more than enough?

[deadastronaut]

which one are you going for?...

with the 'sound to light one' i just split the incoming signal......test with different bright leds to see which best suits your taste...

IIRC 3mm's will go off completely, whereas 5mm's may stay dim....until you play...but i did use 2 leds...for eyes.....

[Dimitree]

I will try the "meatball one" and PRR one and see which I prefer