Invisible LED VU Meter

[quad]

Okay, I've built another copy of the circuit, except the voltage divider is a 1M trim. I'm testing it stand alone. No buffer or any device is engaged. Here's a video and a couple of pictures. The issue still remains. If you pluck a string and let it ring, the LED eventually dies out along with the signal accompanied by a crackling sound in the amp (clearly audible in the video). If you pluck and mute it fast - nothing happens. Any ideas? 
https://www.dropbox.com/s/9h8czea8vdt0l56/MVI_0353.AVI
https://www.dropbox.com/s/7dqjykknf9cw83o/IMG_0354.JPG
https://www.dropbox.com/s/pmsb1v83egvf8b2/IMG_0357.JPG

[waltk]

Good detailed pictures, and I can see/hear what you're talking about on the video.  That helps.

So just to confirm...
the black electrolytic input cap is 2.2 uF?
the yellow cap is a 10uF tantalum?  Is it oriented the right way, with the + side going to pin 7?

I haven't noticed any of mine make that noise.  On yours, it's probably happening every time while the first LED dims.  You just can't hear it when the strings are quickly muted 'cause it happens so fast.

I'll check mine, and see if there's anything I can do to reproduce the issue.  Let you know what I find.

[quad]

the black electrolytic input cap is 2.2 uF?
the yellow cap is a 10uF tantalum?  Is it oriented the right way, with the + side going to pin 7?

I haven't noticed any of mine make that noise.  On yours, it's probably happening every time while the first LED dims.  You just can't hear it when the strings are quickly muted 'cause it happens so fast.

I'll check mine, and see if there's anything I can do to reproduce the issue.  Let you know what I find.

Yeah, it's 2.2 uF. The yellow one is indeed a 10uF tantalum with its positive side facing pin 7 of the chip. True. It crackles as the first LED dims. I took out the capacitor altogether and what happens is a constant crackle. I've also tried a different value of 4.7 uF with the same result. It would be very helpful if you checked how your circuit behaves. 

[waltk]

Quad, I built another one with everything socketed.  I put in components that were as close to yours as I could get, and was unable to cause it to make any sort of noise (even with varying several things).  The chip I'm using is a KA2284 - an AN6884 clone.  Maybe the particular chip you're using is bad or noise-prone.  From the photos, it looks like your layout and build are correct.  So I'm stumped.

[deadastronaut]

@quad:

i thought i'd test my 9 led version too..

i stuck it on breadboard with input/output connected together

and your right i did get a little crackle as the last led faded...i had to turn the fader right up to hear it, but it is there....hmmmm...

it also crackles when just triggering the first led too.....hmmmm bugger.


@walt can you turn your level right up and try it...to test. cheers

[quad]

Interesting. The chip could be the culprit. I've tried a couple of AN6884's and they all behave the same. I think Rob's using these too. Time to get my hands on one of those KA2284 clones.

[deadastronaut]

yes i'm using an6884's too....hmmmm..

if i get time i'll breadboard another 5 led version, and have a look at it...

[waltk]

@walt can you turn your level right up and try it...to test. cheers

Tried that.  Had it cranked up loud enough to cause permanent deafness if I had accidentally hit a string.  No detectable noise (at least not more than the minimal hum from expected from the amp).

[deadastronaut]

hmmmmm.....

[waltk]

more like "Buzzzzzz..." (from the video) 

[Mustachio]

Yeah I noticed the fading out static when I first built this circuit a while ago. Wasn't sure where its coming from but I didnt suspect the IC. I thought possibly it was a ripple across ground while the electro cap drained. And thought isolating ground from my guitar signal and the vu circuit might help.

I built the CP9 comp from tonepad and popped this circuit in with the signal coming from the output jack of the compressor. Overall its fine unless playing really slow long vamped out stuff or at the end of a song letting the last note ring out. I'll try to help get rid of that static ripple as soon as I get a chance.

On a side note, remember those leds start eating up current might wanna run it on its own power supply. I was playing with it and about 4 more pedals on a daisy chain and it caused the psu to give up haha.

[deadastronaut]

^ hmmmm so the ka2284 seems a better choice going by walt's experience of it...unless the smd leds affect it differently somehow ......shame, i bought a few of these .

just for reference :

http://www.e-ele.net/DataSheet/AN6884.pdf

http://pdf1.alldatasheet.com/datasheet-pdf/view/37175/SAMSUNG/KA2284.html

[waltk]

so the ka2284 seems a better choice going by walt's experience of it...unless the smd leds affect it differently somehow

Well, it could be the chip, or it still could be something else (as Mustachio suggested - some kind of ripple from the cap).  I tried some different LEDs; full-size ones, and different colors, so I don't think that's it.  Maybe it's layout-sensitive (unlikely IME), or something outside the circuit - like pickups or amp.

On a side note, remember those leds start eating up current might wanna run it on its own power supply.

On mine, it draws 5 ma with no LEDs on, and 8 ma with all LEDs lit - using a 2.2k resistor.  That's pretty doable on battery.

[Jdansti]

Just based on experience with the 555, which may not apply here, but stick the biggest-ass electrolytic you have from the power pin to ground.  Connect it right at the pin, or as close as you can.

[Gurner]

My inclination here is that pcb/vero layout is going to be key....the incoming signal ground should be as close to the supply ground point as possible (or battery -ve cable) ....and the guitar signal ground should not share the same an6884's  ground return path....it shou dhave its own.

I reckon probably all the LEDs click as they turn on & off (vs just the first LED), but the larger guitar signal will likely mask the click wrt the other LEDs.

What happens when you remove the first LED out of circuit? (I'd imagine the click will go)

[quad]

I've tried placing a capacitor across power - ground right at the pins. Didn't seem to change anything. When it comes to removing the first LED, the 2nd one becomes the last one to crackle, so only the last LED seems to be making noise.

[quad]

Still waiting for those chips. If that won't work, I might play with the layout a little bit. In the meantime my Crybaby wah-wah is taking in some serious mojo.   I couldn't find a sole 4uF capacitor. Ridiculous. It sounds alright with all the modifications. A little more wah'wah-y instead of woh-woh.
https://www.dropbox.com/s/ly3hl0y5dfp0od2/IMG_0365.JPG

[quad]

Hey waltk,

I've got your package. Really appreciate it.  So far I've tested the SMD board and swapped the chip on my old board. The SMD board crackles in the same way, swapping the chip made the noise less noticeable, but it's still there.

[waltk]

OK.  So to summarize, using the KA2284 instead of the AN6884 seemed to help a little in one scenario, and not at all in the other.  My own experiments have all been dead quiet.  It must be something outside of and/or interacting with the circuit.  Something about the guitar pickups or the amp is different for you.  It would be nice to know what causes the noise for you and not for me, but it's kind of hard to tell without being able to reproduce it.  Oh well - let us know if you discover anything else.

[Mustachio]

Oh Yeah I forgot to post about this again. After I posted last time in this thread I went down stairs and plugged the pedal back in and tested it.... No click or any audible sounds at all in fact a very dead silent pedal(ibanez cp9 layout from tonepad) .

And I remembered last time I fiddled with it I set the trim pot up a bit higher so the leds where not as responsive as they could be yet still gave me a full reaction when I strummed hard. So there ya go fiddle with that trim pot. I'm sure there could be improvements to how we use the an6884, but overall it works great and is simple and cheap! I'll have to take a look at those other KA chips some time they look neat!