Searching for a simple envelope detector only, with LED(s)

[KarenColumbo]

Dear gents, extracting an envelope detector/follower circuit out of a complete schematic like e.g. an Autowah brings me out of my depths. I'd love to have such a detector circuit that varies an LED's brightness depending on the volume of the input signal. Can you help me out here?

I studied the famous Dr- Quack, but this is an entirely different shoe - it seems there is some transistor working as a variable resistor or something. This would be nice, too, since I want to have a variable resistor depending on the attack, but I don't need the filter at all.

[EBK]

Have you looked at this? http://www.geofex.com/Article_Folders/FXbus/fxbmod06.htm

[Mark Hammer]

That simple rectifier circuit works just fine with an LED.  In fact, I made my younger son a "robot" mask to wear for Halloween a decade back, in which I installed a little electret mic as the input of that circuit, and used the circuit to drive two "robot-eye" LEDs in the full-head assembly that glowed in sync with his voice.

So you should have little problem driving an LED with that same circuit.  Just be mindful of current needs/limits and choose your LEDs carefully.

For instance, the Anderton Bi-Filter project here uses a very similar rectified/follower (adding a sort of "Bias" control to set the minimum filter start point) drives a pair of LEDs directly, with some current-limiting resistance just ahead of the LEDs.

[KarenColumbo]

Have you looked at this? http://www.geofex.com/Article_Folders/FXbus/fxbmod06.htm

I have, but here the detector puts out voltage, not light - I wouldnt know how to scale it correctly

[KarenColumbo]

That simple rectifier circuit works just fine with an LED.  In fact, I made my younger son a "robot" mask to wear for Halloween a decade back, in which I installed a little electret mic as the input of that circuit, and used the circuit to drive two "robot-eye" LEDs in the full-head assembly that glowed in sync with his voice.

So you should have little problem driving an LED with that same circuit.  Just be mindful of current needs/limits and choose your LEDs carefully.

For instance, the Anderton Bi-Filter project here uses a very similar rectified/follower (adding a sort of "Bias" control to set the minimum filter start point) drives a pair of LEDs directly, with some current-limiting resistance just ahead of the LEDs.

Thank you! Do you think it would work with a single sided supply and virtual earth?

[Mark Hammer]

Throw a charge pump at it.  That's what folks do for Mu-Trons.

[digi2t]

The Bixonix Expandora 2001 has a detector circuit, but in a VU meter format. 4 LED's if memory serves me correctly. I might have the schematic in my gallery. If not, PM me and I'll post it.

Here you go;



The detector part of the circuit is in the lower right corner of the schematic.

[Kipper4]

You know this guy right Andreas.

http://sound.whsites.net/appnotes/an001.htm

Keep it simple. Those at the bottom of the page are probably overkill for our needs.
Depending on the application .

Ic2A in the schematic Mark Hammer posted is the rectifier.

Now compare it to the rod Elliot page.
Go look at some other enveloped effects see if you can now see the rectifiers.

Google half wave , full wave, charge pump rectifiers.

I hope this helps.

Rich

[KarenColumbo]

You know this guy right Andreas.

http://sound.whsites.net/appnotes/an001.htm

Keep it simple. Those at the bottom of the page are probably overkill for our needs.
Depending on the application .

Ic2A in the schematic Mark Hammer posted is the rectifier.

Now compare it to the rod Elliot page.
Go look at some other enveloped effects see if you can now see the rectifiers.

Google half wave , full wave, charge pump rectifiers.

I hope this helps.

Rich

Yo, Rich, I already got it working - if somewhat iffy

I just used this circuit from Rod Elliott:

I put a 4u7 polcap after R4 and a 100k pot right after this as a variable resistor to ground to take away some of the juice.
LED is lighting up fine

Now what I would like to do is making the LED's brightness more correspondent with the input volume. So if I pick hard, the LED should light up brighter and go down fast. I don't care about ripple, this thing will drive a filter's intensity, not the frequency.

How would I go about making the brightness differences more extreme? Maybe some sort of "soft noisegate"?

[KarenColumbo]

Wait .. could it be that I'm trying something like the Expandora without knowing? 

[KarenColumbo]

A bit of reading brought me to "Stompboxology", the Envelope issue.

It took this little circuit here:


Instead of putting them to Vref I grounded those parts and put a red LED between output and ground. Which reacts very fine and fast and not a lot of ripple. So cool <3

Edit: I drive the whole thing with the first gainstage of "Highway 89" by legendary Doug Hammond. I go directly from the RGAIN wiper into C1 of the Sompoboxolgy circuit.


Instead of 5089ies I use BC249B. They drive a fine Overdrive, but the circuit is VERY quiet now. A fluke, if I might say so.

[Kipper4]

I wouldn't put the charge cap your 4u7 after R4.
I'd stick an led anode to rods output cathode to clr>gnd.

Led light intensity is largely currant dependant.

Now more parts might come into it. Led driver. Op amp or transistor driver.
It may get help with the led.

Go down fast. Smaller charge cap?
Go down fast smaller 100k pot. This is the decay pot after the charge cap.
The less resistance there is for decay the faster the charge cap will discharge.

Which op amp are you using for the rectifier?

[Kipper4]

Take a look here.

http://www.diystompboxes.com/smfforum/index.php?topic=117652.msg1093012#msg1093012

[KarenColumbo]

I use on half of a 5532.

Here's a little video of how it's reacting to strat input.

http://www.mrscolumbo.com/uploads/envelope.mp4

[Kipper4]

Maybe try a lm358 too.

It looks like it's reacting fairly well. You can see the ripple when the led lights back up on the decaying signal in your video.


So if I've got this right you intend to control the q of a filter with an ldr?

[KarenColumbo]

nah, just the boost of a bandpass. sort of a fixed wah