Flatline compressor LED staying on

[MrStab]

hi guys,

i built the Flatline compressor yesterday - twice, technically, as i wrongly thought a rebuild would be faster than debugging - and everything worked great, but there was a loose connection somewhere and now after much turd-polishing, the LED just stays on and doesn't react to the guitar input. i used this schematic: http://www.sabrotone.com/wp-content/uploads/2011/10/Flatline.gif

the actual effect seems to work fine, and it's affected by me covering up the LDR and turning the sustain pots, but no dice with the LED. so given my limited knowledge of all this, i'm guessing it's sometime after (or during) the signal splitting in two, right? i tried making an audio probe, but it doesn't seem to make any sound through this circuit.

i have a list of voltages from everything but the resistors because i'm lazy (but happy to provide em if needed). i subbed a 1n4001 for one of the diodes (measured roughly twice the resistance) but as i say, it all worked fine before regardless of this.

voltages (i used a mains adaptor set to 9v in case it gave more precise readings):

9v input 9.9

Caps (from positive terminal):
c1 0
c2 4.91
c3 4.93
c4 9.9
c5 9.9
c6 7.84


TL072 pins:
1 4.93
2 4.93
3 1
4 0
5 4.91
6 6.62
7 6.62
8 9.9

Diodes (positive - negative):

2 6.62-9.9 (1N34A)
3 7.84-6.62 (1N34A)
4 7.84-8.33 (1N34A)
5 8.97-8.33 (1n4001)

would really appreciate any help, & will offer anymore info as required.

cheers!

[Kipper4]

some one will have posted the correct voltages somewhere. Did you google it?
You'd probably be better doing a full what to do ,debugg list too.
Not that i'm an expert, i'm just a newbie.

[MrStab]

i Googled like a madman - all i can find are voltages from other people who have (different) problems with it!! lol

pretty much followed the debug list to get to this point. either i'm not using the audio probe right, or its use is limited in a compressor circuit. thanks for the suggestions, though.

i'm tempted to think one of my diodes burnt out, but i successfully tested them all with a multimeter and haven't really applied much excessive heat or pressure to that region. but the voltages on the diodes seem weird-not that i really know. polarity is all correct, hasn't been changed since it did work.

[Kipper4]

did you use the reccomended LDR?

[Kipper4]

I'm sure MR Patton will sort you out.

[MrStab]

*suddenly figures out how to use audio probe properly* lol

the LDR itself is working fine - the values for that seemed variable from my (poor) research - but that part of the circuit seems to work fine. as i predicted, something seems off on the B side of the TL072. i'll report back!

[MrStab]

using the audio probe, the signal dies at R1/4 (both 10M). you can hear the signal on one terminal but not the other. i'm talking the legs themselves, not just where they make contact with the board. wtf? i even replaced the resistor to no avail.

also, i was getting a signal near the diodes at first, but not anymore. it's just a disaster. lol
at least the "A" half of the opamp & all associated with that seems fine... for now.

it's really discouraging when you hype yourself up for this stuff, it fails, and you have to draw the line at spending weeks getting it working, if it will even at all :/

[deadastronaut]

you do have a cut under C1 right?...

you say it worked fine, but stopped after a loose connection?...maybe reflow the solder joints.

Hang on in there....

[MrStab]

definitely a cut under C1 - i've pretty much memorised all the cuts, they're like some kind of star constellation! lol.

whilst replacing R1, i screwed up one corner of the vero/stripboard quite a bit - thankfully not near the diodes, but if i can't jumper over the row then it's probably game over. the only board i have left isn't wide enough, i doubt i have enough solder for a complete rebuild & i'm gonna be unable to buy more for at least a few days - not to mention replacement parts. can't believe i built it twice and ruined it twice! lol

[MrStab]

just in case i do fix the mess i've made:

is it possible that a diode(s) failing could've caused the power to just go through and keep the LED on? i ruled this out at first because i had the same problem, only caused by shorts prior to the short time when it worked. and i guess it just didn't really occur to me.

[Kipper4]

Hang in there. You'll find it.

[MrStab]

just noticed i screwed up the position of a few things. painfully obvious things. which makes the fact that it worked to begin with quite creepy. in any case, i'll try fixing it when i wake up later, given the previous damages can be recovered from

[MrStab]

moved some stuff around, now the LED stays on but reacts to the guitar! kinda like the opposite of what it's meant to do, but still - progress! lol i'll probe & volt-test that mofo but any ideas in the meantime?

all 3 of my threads here have been painfully amateurish and full of stupid mistakes, sorry bout that! still stumped though.

[bluebunny]

You do have R7 (LDR) and D1 (LED) optically connected, and shut off from any outside light?  It's just that you mention seeing the LED lighting up, which you wouldn't if it were hidden away...

[MrStab]

even though the LDR would be useless unless covered, shouldn't the LED operate independently? i've tried blocking off the LDR completely, and all that does is affect the tone, not the LED on the other side.

just to be sure: am i right in thinking that the light should flash on then fade out as soon as you switch it on, and that while receiving no signal, the LED should be off? it doesn't flash when turned on. i'm having some difficulty with the audio probe because i'm a bit of a moron, but vague observations suggest the signal dies somewhere around the diodes. D5 seems to work fine, i'm working on more info. but how would a failed diode keep the LED on? it's probably really obvious, but it seems counter-intuitive to me. i guess dying vacuum tubes can still do something if they're screwed, maybe it's a bit like that.

i've only had 2 cuts, 1 burn and 1 electric shock from this project, so it's going well so far even if i only wind up with a distortion pedal. lol thanks for all the help so far guys!

[MrStab]

there's signal going to all the diodes. *sigh*
so, the the whole LED section seems to work in reverse (inc. fading ON when powered up)... maybe i've screwed up polarity somewhere? the polarity stripe on some of the diodes were hard to see, but i did use a multimeter to work out the right way beforehand. worth checking?

Edit: nope, they're all in the right way...

[samhay]

Might be time to post photos.

[MrStab]

erm, i'm kinda embarrassed to submit photos as i almost always do a really scruffy job with this stuff, but i usually manage to get it working lol. you should see the back of my Crybaby PCB... i wouldn't mind the inevitable being told to start again & learn not to be shaky and clumsy, but i'd rather get this one working first before i do so. just so i have a better understanding of the circuit.

i guess unless i get over that hangup i'm pretty screwed. i'll have a look around for even worse soldering skills than mine and see if that lowered bar improves my confidence. lol

now the LED flashes when powered on, and i have some screechy modulation-esque sound when i switch it on. *sigh*

[midwayfair]

there's signal going to all the diodes. *sigh*
so, the the whole LED section seems to work in reverse (inc. fading ON when powered up)... maybe i've screwed up polarity somewhere? the polarity stripe on some of the diodes were hard to see, but i did use a multimeter to work out the right way beforehand. worth checking?

Edit: nope, they're all in the right way...

Is the LED backwards? Is the 100uF cap in correctly? It should have its cathode connected to the anodes of two of the diodes, and its anode should be connected to the cathodes of two other diodes. The + side of the 100uF cap should be connected to the LED's anode, and its negative side should be facing the cathode.

Why would you think the signal dies "somewhere around the diodes"? The signal is what turns on the LED. Anyway, you should have signal at pins 1 and 7 as normal, also on both sides of the 330R.

[MrStab]

thanks for the suggestions, Midway.

just tried probing either side of R10 (330R) as suggested - it's all there. same with either side of each diode (although some sides seem to have kick-ass distortion while the other ends are clean, but i guess that's a diode thing lol) and i tried holding the pins of another LED against the original to see if there was any reaction - one way it lights up, the other way it doesn't. unless maybe i do have the LED round the wrong way and  there's another fault? worth mentioning that this problem started before i replaced the LED, though.

pins 1 & 7 of opamp coming through fine, too. C6 (100uf) also seems to be in right, surrounded by a trace above and 2 to the right. negative facing "north" as per schematic.

i suggested the diodes because frankly i'm just peeing into the wind a bit here and am an extreme novice. lol