Guitar LED circuit sucking tone

[MrStab]

i think we're more on the same page than it might seem, e.g my "can probably ignore..." comment bout the LM386.

all i can think of is one of the resistors must be screwed - i get how this circuit works, i've built one before, but i guess it just seems intuitively "far out" to me that it's something as trivial as a resistor failure. only one way to find out, i suppose...!

DMM is fine as i've been using it on other things all day, no "foreign objects" at the junction... screw it, i'm gonna try swapping out the top resistor.

[artifus]

hope this helps - not trying to teach grandma to suck eggs.

[Gurner]

i think we're more on the same page than it might seem, e.g my "can probably ignore..." comment bout the LM386.

all i can think of is one of the resistors must be screwed - i get how this circuit works, i've built one before, but i guess it just seems intuitively "far out" to me that it's something as trivial as a resistor failure. only one way to find out, i suppose...!

DMM is fine as i've been using it on other things all day, no "foreign objects" at the junction... screw it, i'm gonna try swapping out the top resistor.

If you've DMM, then measure each resistor in circuit (if you've nothing else connected then they should read correct @2.2M), then measure across both resistors in total (you should get 4.4M)... I think what'll be key here is the result you get  between the ground & the junction of the resistors.

[MrStab]

i really, really appreciate the help and i am definitely just a beginner, but i know how the whole voltage divider/buffer thing works. i've successfully built the AMZ buffer on its own, and i've (somehow) built a working compressor & delay which also utilise buffers, so i suck but increasingly less-so! lol.

while i might have misunderstood a lot of what i'm being asked to do, i am fairly certain there is some less-common anomaly with this circuit. be it a tiny, nanoscopic short or whatever, there is something wrong with this one which is not immediately obvious. i've swapped out pretty much every component in the circuit, quadruple-checked their positions, eaten more shorts than an authority figure to Bart Simpson, and i've even (rightfully) started to doubt what i've learned so far altogether. maybe it's just a simple mistake, but more to do with my perception than my understanding.

my DMM only reads up to 2000k, so while the vendor had marked the 2.2M resistors, i went by colour codes and ensured that they were out of range on the meter. i have slight colourblindness, which usually doesn't interfere, but if the values can be inferred from the photo i uploaded then i'd appreciate it if someone could confirm. just replaced both those resistors to no avail.

[Gurner]

The resistors as seen in you pic look fine (red, red, black, yellow)

if your DMM only reads up to 200k....as a temporary measure, you could always place some lower value resistors inplace of the 2.2M resistors ...say 100k    ...at least then you can get to the bottom of the problem.

[deadastronaut]

hi grant,+ guys..

wouldn't this buffer work....one signal into buffer then sound to light?....other signal as normal out?

or...couldn't a diode into the 386 sort it?.....or do i need more whiskey.  

http://www.google.co.uk/imgres?imgurl=http://www.beavisaudio.com/techpages/Buffers/BuildOneBuffer.gif&imgrefurl=http://www.beavisaudio.com/techpages/Buffers/&h=1726&w=2551&sz=243&tbnid=59lZXfcyZtIuZM:&tbnh=88&tbnw=130&zoom=1&usg=__o8qAnMTG_yTqmAnz8TA4N_ukDPU=&docid=pvENDEZUtJxYNM&hl=en&sa=X&ei=ByFjUeHpI-ez0QXPkIGIBA&ved=0CDkQ9QEwAA&dur=2378

[Gurner]

Hi Rob,

in essence that's sorta the buffer variant Grant is using...the problem is with the two resistors connected to the opamp +ve pin ...they no workee     ...."more Glenffidich sir"?

[deadastronaut]

ahhh i see...more ''famous grouse'' i think..

[MrStab]

for some reason i said 2000k instead of just 2M re. my multimeter, it's a piece of crap but it does more than 200k! lol

i do have a coupla 1M resistors lying around which i've seen used in a few schematics instead of 2.2, but i feel as though that's making the assumption that the whole strip of 10 resistors was mis-coded. does that happen? wouldn't wanna be the jury in any exciting, action-packed lawsuits stemming from that!

tomorrow (well, today technically) i'm gonna either cut the thing in half and/or just start over separately. if i did manage to get the voltage halved as it should be, i'd still have to deal with the fact that hooking up the LM386 seems to half the input voltage. even though it didn't originally... i think this circuit is haunted.
i probably sound like a stuck record here, but do the facts that A. the max voltage is halved with the 386 connected, but B. when it's disconnected & voltage is back to 9v, pins 1 & 2 on the TL072 read 4.5ish offer any clues? just because in both those instances it's that voltage we're looking for, and i am totally out of ideas.

i dunno. i don't drink in favour of other party materials, but all this is making me think maybe i should start again. pass the whiskey. lol

[Gurner]

Those other 'facts' need addressing (your LM386 should not drag the supply voltage down - there's another fault for later on to sort!), but there's little point looking at them yet (& they aren't related to your immediate problem). Also, the fact that pins 2 & 3 have the right voltages is probably just a fluke...because unless your input voltage on pin 3 is correct, then they might as well be way out - it matters not.

Like I say, you need to build on solid foundations...one step at a time...and what better way to start at the left of the circuit (input) get that working & then work your way towards the output.

And at the risk of also sounding like a broken record, your input voltage on pin 3 is wrong & needs to be sorted first     ...& to make matters worse, you are gonna be up against it if you've not got a DVM that's capable of measuring the resistances in play.

[MrStab]

i do get the situation, i've just run out of ideas, so intuition and logic are long gone here. lol

all i really have left to try is 1M resistors for readings' sake, or just starting over. i'm bored, i'll switch out the resistors just now (again!)

[MrStab]

1M resistors bring the junction/pin 3 to ~2.9V

tested resistance whilst in the circuit, both add up to 2M

[Gurner]

1M resistors bring the junction/pin 3 to ~2.9V

tested resistance whilst in the circuit, both add up to 2M

Without knowing what your supply voltage is, it's difficult to say whether that's correct or not...so you now have 2.9V at the resistos' junction....do you have about 5.8V at the top of the top resistor?

[samhay]

Just dipping in here, so forgive me if I've missed something.
Using large 1M+ resistors to create a bias voltage when there is something else sucking enough current to load down the power supply is going to potentially cause problems - they are too big. How about trying 10-100k resistors with an optional 1M from their junction (4.5V) to the op-amp?

[MrStab]

supply voltage is approx 8.75v coming into the circuit. the top of the top resistor is 8.75, bottom is 2.9.

i've cut the 386 out entirely, even input & ground. got a few mV more but nothing significant. so hopefully now we can assume i've just done something really stupid. lol

Edit: tried testing pin 3 with IC removed again, still reads 2.9

[MrStab]

sorry guys, i feel like i'm wasting your time here as this is a bit like flogging a dead horse. if we haven't cracked it by now, given the simplicity involved, i'm not sure we ever will. something insanely dumb has happened, or extreme bad luck, but either way i can't really see how the hell this is happening.

i'm up for still trying to crack it if anyone else is, but  i'm not at all opposed to calling it quits and starting over. in any case, thanks a ton for the help everyone, especially Gurner!

[Gurner]

sorry guys, i feel like i'm wasting your time here as this is a bit like flogging a dead horse. if we haven't cracked it by now, given the simplicity involved, i'm not sure we ever will. something insanely dumb has happened, or extreme bad luck, but either way i can't really see how the hell this is happening.

i'm up for still trying to crack it if anyone else is, but  i'm not at all opposed to calling it quits and starting over. in any case, thanks a ton for the help everyone, especially Gurner!

Well, it still doesn't add up!!

I don't suppose you've a breadboard handy? If so....

9V
|
top resistor (1M)
|
----measure here   (should be 4.5V)
|
bottom resistor (1M)
|
0V

At least that way, you've proved your resistors!

[MrStab]

no breadboard unfortunately, but i've tried 6-8 resistors now, inc. ones with guaranteed values. i can only assume there's a nanoscopic (or metaphysical?!) solder bridge or something on the stripboard i've used. prolly just gonna start over, do two separate boards and wire em together. so weird!! definitely doesn't add up!

[MrStab]

okay so same thing happened on rebuilding the buffer, so i made just a raw voltage divider aaaand... same thing.

neither 1M resistors from source A, or 2.2M from source B show 4.5v. on different batteries. in the setup you outlined, Gurner. bearing in mind the 1M's are guaranteed 1M's! also changed the battery in my multimeter. nada.

*shrug*

[deadastronaut]

'grant:  have you a schematic drawn up.?..rather than a vero layout....it'll be easier for everyone to see where your problem lies..

invest in a breadboard...an essential and  great tool.