Hello,
I have an acrylic fat strat I frankensteined together for shows and added a small, op-amp based circuit that contols 4 LEDs behind the pick guard. Trouble is, this circuit is cutting off some of the high end of the signal. I cant just throw in a bypass switch because I want the tone to be corrected when the circuit is active too. Raising the input impedence destroys the desired LED effect. Would a FET based input buffer help or perhaps I need to rearrange the circuit layout?
Thanks
Circuit is set up like this:
Pickup_________________________Output
|
|____OpAmp____
|
Gnd
Pic:
(http://i53.photobucket.com/albums/g51/zibrazibra/NeonAx1.jpg)
A buffer should do the job, from pickups into buffer output of buffer to opamp and output, that would probably stop the opamp circuit causing tonesuck.
If you posted your circuit someone can probably figure out a way to stop it causing the problem though ;)
Looks very cool by the way.
Yeah, just insert a buffer before anything happens! You've already got the power in there.
Is the op-amp in an inverting or non-inverting config?
Its non-inverting, just a 386 for attack sensitivity. I just built a wah that features j201 based buffers, do you think something like that would suffice? I have all the parts available.
Thanks.
The 386 has quite a low input impedance, about 50k I think, so a buffer in front is probably the easiest solution.
A simple J201 buffer will do the job fine, there's some good examples here http://www.muzique.com/lab/buffers.htm (http://www.muzique.com/lab/buffers.htm).
Excellent. Thanks for the pointers.
Quote from: T-Flex on July 19, 2011, 02:07:18 PM
Its non-inverting, just a 386 for attack sensitivity. I just built a wah that features j201 based buffers, do you think something like that would suffice? I have all the parts available.
Thanks.
I agree with slacker, a Jfet buffer will be fine.
Just FYI an LM386 is not an op-amp. It's a special function amplifier chip that just happens to connect in a convinient op-amp style way.
not to dig up two dead threads in one day or anything... but i was wondering if the buffer required to make this work would definitely need to be placed before the signal splits, or if it could be placed after (so just before the LED circuit)? i think it's already been implied twice that it needs to be before anything happens, but if so, is there no contingency to keep the audio signal independent besides a separate battery for the buffer (or fast switch-flicking)?
gonna just make a simple TL072 buffer, hoping it'll be as transparent as possible.
cheers!
I'm not sure what you mean by keeping the audio signal independant.
If you want you can put the buffer after you've split the signal. The input of the buffer will then be in parallel with what ever you plug the guitar into but if you make it have a high input impedance this won't noticably affect the sound.
ideally i wouldn't want the signal coming out of the guitar to pass through the buffer at all, i guess what i'm asking is can that be done?
i know this prolly demonstrates a poor understanding of impedance, but what better way to learn than flashy things! i can afford some leeway in terms of screw-ups as it's not my primary gigging guitar.
Imagine a Y cable** ...one leg of the Y goes to your guitar amp as normal, the other leg goes to a buffer.....
_______ To guitar amplifier as normal.
pickup signal-------|
--------- to a 'buffer' circuit feeding the LED board.
Signal does not pass through the buffer.
Buffer (feeding your LED circuit) does not load the signal.
Job done.
(**it's probably better described 'T off' ...as i just when you 'T off' a pipe from say a main water pipe)
dude, you summed that up perfectly! thanks a lot, i was unsure as my braindead intuition made me think "hmm, thing fix sound. thing go right at start just in case."
out of curiosity, would it even work if you did pass it through the buffer first and then split? or is it just the same-o?
parts should arrive on saturday or monday hopefully. my concerns now will probably be any possible interference from the LED's being in close proximity to the (unpotted) pickups and routing everything. if tone-shaping transparency isn't an issue anymore, i can build the laziest POS buffer imaginable. lol
It works either way, one advantage of splitting the signal before the buffer is your guitar will still work if the battery powering the buffer dies, if you took the signal from after the buffer it would only work if it had power.
interesting...
@G: so thats why i had a little , but noticable interference when using the 'Y' with the 386 on the diy sustainer then?.. :icon_idea:
good to know, Iain - so turns out it's advantageous in another way altogether to not screw with the tone.
it was your thread where i first heard about using the LM386 for this purpose, Rob. talking of which, i've tried combining a similar schematic (modified? i "credited" your name for it either way!) i found with a simple buffer from Muzique.com. reckon it'll work? there are probably some glaring mistakes there, feel free to mock!
(http://i.imgur.com/9xLOL3y.jpg)
Quote from: deadastronaut on April 04, 2013, 01:57:25 PM
interesting...
@G: so thats why i had a little , but noticable interference when using the 'Y' with the 386 on the diy sustainer then?.. :icon_idea:
Hard for me to say (cos I don't know your exact circuit situation), but for any sustainer circuit essentially what you are doing is that same as outlined in my last post - you're essentially T'ing off the guitar signal to a sustainer circuit, which has a buffer at the front so as not to colour the original guitar signal. An LM386's input impedance is too low for a typical guitar pickup - it needs a buffer in front of it ...else your tone-age will be full of suckage.
Quote from: MrStab on April 04, 2013, 12:46:04 PM
my concerns now will probably be any possible interference from the LED's being in close proximity to the (unpotted) pickups and routing everything. if tone-shaping transparency isn't an issue anymore, i can build the laziest POS buffer imaginable. lol
If your pups are single coil & your LEDS are too close, then yes, you'll get interference. Humbuckers are more foregiving.
Re the circuit you intend using....I think 4 LEDs in series as shown might be a stretch (possibly *just get away with it with RED leds, but it won't driver blue, green, white LEDs etc)
Quote from: Gurner on April 04, 2013, 02:34:18 PM
If your pups are single coil & your LEDS are too close, then yes, you'll get interference. Humbuckers are more foregiving.
Re the circuit you intend using....I think 4 LEDs in series as shown might be a stretch (possibly *just get away with it with RED leds, but it won't driver blue, green, white LEDs etc)
i'm a humbucker guy so i have that on my side. duly noted about the quantity, i'm guessing the only solution would be a trade-off between resistance and brightness? prolly not much room for reflections in the pickup slots, but maybe i can find way to spread out the light of a lesser amount of LEDs
@G: cheers man, i'll try that when i blow the dust off it.. ;D.
lack of current resistor(s) and unrealistic amount of series LEDs aside, anyone see any fatal flaws in the layout i posted? ( http://i.imgur.com/9xLOL3y.jpg ). i just built it and am trying to establish whether it's the layout or the build that's wrong. not sure if the original voltages from either "half" of the circuit would apply here, if the whole thing's merged. would be cool to have this whole thing on one piece of strip/vero.
it's hooked up to a 1/4" plug to test post-guitar, atm, although i doubt that'd prevent it from working at all. i did overheat an LM386, but shoved a 220uF output cap in there and replaced it, and it seems okay now, so that doesn't seem to be it. just doesnt do anything! lol
This is one of those circuits that's a kludge at best!
Ok, with no AC signal present, the LM386 is going to have half the power supply on its output pin. Therefore for 9V there's going to be 4.5V sitting on the output pin.
From what I can gather, the trick with this circuit, will be to make sure you use just enough LEDs so that they are just visibly'off' with no AC signal present....and that's where the problem starts creeping in.
RED LED fwd voltage is about 2V .... so for the 4.5V present on the LM386 output pin two LEDs would be too little, three would be too many
Blue LED fwd voltage is about 3.3V .....1 LED would be to little, two would be too many.
What I'd be inclined to do (just as a starter & experiment), is remove the output cap, & connect two blue leds (or any other led with a fwd voltage greater than 2.5V) ....if you've connected everything right, they should be off. whack your guitar & they should light up.
What I'd probably do first though is connect a speaker *with* the output cap in situ, just to make sure you han hear someting on the output & to provie the circuit is working.
Get rid of the blue jumper between the 220uF cap and D1, that is connecting the output straight to ground so it won't do anything. Apart from that, taking into account Gurner's comments it should work.
Pin 5 of the buffer should be connected to pin 3 to keep the unused half of the opamp stable but that won't stop it working.
Quote from: slacker on April 07, 2013, 08:55:08 AM
Get rid of the blue jumper between the 220uF cap and D1, that is connecting the output straight to ground so it won't do anything.
Good spot (& might account for why the LM386 is getting hot - all AC signal is getting shunted to ground!)
Mr Stab, try removing that jumper as per slacker's suggestion & seeing if it works, before trying my 'experiment' out.
i should probably have built each circuit separately....
just before reading either of your posts, i removed the buffer-side output cap (10uF). i've removed the 220uF as well, and cut the jumper to ground just after where it was. now the two blue LED's stay on. dimly lit (no resistor yet, for some reason...). it's a start at least! i had one short which caused no voltage readings but since fixed it, no more obvious shorts from continuity test.
worth replacing the LM386? i have 3, i'm guessing the first one is toast, though. only had one IC socket spare so the TL072 is "perma-installed", but fingers crossed i dont have too bad a track record with op amps.
my only unused battery's reading 6.3 but im gonna go score some more in about an hour.
Well unless you have a scope I'd be inclined to put a loudspeaker on the output of the lm386 *with* the 200uf output cap in place - until you get some AC signal out of the lm386 this cct is never gonna work (& how will you know unless you put a speaker on there?). If I were a betting man, I'd say you've likely nuked your LM386 with that AC short to ground (i.e. that jumper link you had in place....you did say it got very hot)
If you post your DC reading for your opamp pins, that'll lend a view as to whether they're working or not.
i replaced the original chip after it overheated, was unsure if maybe the 2nd one had screwed up as well, though.
any ratings i should look out for, or would some generic old computer speaker suffice? i guess i just hook it up as though it were one of the LEDs, in this circumstance. i'll have a look around just now, in the meantime here're voltages taken from a fresh battery:
TL072
4.68
4.68
2.23
0
0
8.71
8.71
9.31
LM386
3.3
0
4.64
0
7.55
8.23
9.25
0
cheers!
so i hooked up a little speaker (8ohm / 2W rating, tested with "ye olde battery trick") in place of the LEDS, restored the 220uF cap, and now the LM386 is getting hot again.
in an hour or so i'm gonna try removing that IC & try an audio probe to test if the buffer's working, at least
Quote from: MrStab on April 07, 2013, 12:45:01 PM
TL072
4.68
4.68
2.23
0
0
8.71
8.71
9.31
LM386
3.3
0
4.64
0
7.55
8.23
9.25
0
Do you have a schem vs. just a board layout? (it hurts my eyes & brain trying to map/visualize the circuit in my head).
As a starter, pin 3 of the tl072 aint right...it should be about half your supply voltage ....are you sure you measured it right? If so, I'd be inclined to desolder your tl072 & see if that voltage on pin 3 rights itself (if so, your tl072 is probably bust). In turn pin 1 & 2 should replicate whatever DC is on pin 3...so something wrong there too (although it is sitting near 1/2 VCC, which makes me wonder if your pin 3 reading is right?)
okay, the whole thing is screwing up now. but that's part of the "fun".... lol
observations!
-the TL072 voltages had become way weirder, 1.42 on pins 1 & 2 and 0.98 on pin 3, so i replaced it to no avail. could a failure on the other IC be affecting readings on this one? i only have one LM386 left!
-the speaker being connected made the LM386 overheat, but when i hooked up the LEDs again instead, it seems fine.
Edit: sorry, Gurner - forgot about the schematic. i don't have one per se, but for all intents & purposes it's just meant to be a combination of this basic buffer: http://www.muzique.com/images/buff8.gif (w/ 2.2 instead of 1M for divider resistor values), and this artistic masterpiece i found on the web: http://img.photobucket.com/albums/v17/un_zipped/guitopam.jpg (except for the speaker). output from the former into input of the latter, all common grounds etc.
Quote from: MrStab on April 07, 2013, 03:08:41 PM
okay, the whole thing is screwing up now. but that's part of the "fun".... lol
observations!
-the TL072 voltages had become way weirder, 1.42 on pins 1 & 2 and 0.98 on pin 3, so i replaced it to no avail. could a failure on the other IC be affecting readings on this one? i only have one LM386 left!
-the speaker being connected made the LM386 overheat, but when i hooked up the LEDs again instead, it seems fine.
Edit: sorry, Gurner - forgot about the schematic. i don't have one per se, but for all intents & purposes it's just meant to be a combination of this basic buffer: http://www.muzique.com/images/buff8.gif (w/ 2.2 instead of 1M for divider resistor values), and this artistic masterpiece i found on the web: http://img.photobucket.com/albums/v17/un_zipped/guitopam.jpg (except for the speaker). output from the former into input of the latter, all common grounds etc.
I know your tl072 is soldered in, but still IMHO that puppy needs to come out (or at least the pin 3 leg pulled out) to test the dc voltage on pin 3 with the tl072 removed ....you need to see the junction of the two 2.2M resistors be at half your supply ....this ain't gonna work until you have have about 4.5V on pin3, 4.5V on pin 1 & pin2 ....something is dragging the voltage on pin 3 down - easiest way to get to the bottom of it, is to remove the tl072 & see what you got then....
when i replaced the TL072, i put an IC socket in, so it being soldered in is no longer a problem. i've just removed pin 3, bent it upwards and nothing's touching it, but it still reads 0.98 and pins 1 & 2 are 1.4. ...aaaand i've just snapped off pin 3. damnit. lol
a huge clue as you suggest is the fact that the voltage isn't being halved. i'll have another wee look & try to get a photo(s) maybe
to be clear....you are measuring the vacated pin 3 hole (not pin 3 on the opamp itself)... re why you aren't getting 4.5V at pin 3, well there's not a lot of components involved so it ought to be easy to find. ....you could try unsoldering the cap feeding to the junction of your two 2.2M resistors.
my bad - just tried that and got a clear 0 on that pin socket :S . i accidentally broke the 3rd leg off another opamp in the process, that's commitment! lol
tried disconnecting the 100nF input cap, if that's what you meant - while the voltages did seem to fluctuate higher for a moment, pins 1 & 2 settled back down at the same 1.4-ish. i replaced the 10uF electrolytic which comes after that with a jumper early-on, unless you meant that one.
you're right, this is probably a lot easier than i'm making it... here's a pic anyway! some sketchy hookup wiring, but i'll fix that at some point... (still no shorts obvious to me or a DMM)
(http://i.imgur.com/4CWtFbc.jpg)
I'm now not following what you're saying/doing ...but now that I can see your board - just remove the tl072 totally....measure the voltage on pin3 of the (empty) IC socket - do not proceed or put the tl072 back in place until that pin 3 on the IC socket measures approx 4.5V!
If you are now saying pin3 is 0V, then that isn't right either. There's only two resistors involved....one resistor is connected to 9V, the other to 0V ...they meet in the middle where there should be 4.5V....but you are saying there's now 0V? (or are you saying there's something else?!)
my bad, i'm a generally confusing person but i've been ill the past coupla days so twice the loss of brain functionality! i'm a bit slow on the uptake.
removed the TL072 altogether, pin 3 voltage is still 0.
power goes in at full voltage (8.4), measures 2v after the first 2.2M resistor, then the voltage drops to the culprit 0.98 on the jumper connecting that to pin 3. looking back on my previous readings, i don't understand how the whole thing has changed now, only thing i can think of is that 1-2 of the LM386's were fried, but could that even affect the voltages on the other side of the board?
the whole thing just makes no sense to me anymore, as simple as it is. i have no clue how the hell those voltages have changed & why i can't fix pin 3.
Quote from: MrStab on April 08, 2013, 08:40:33 AM
removed the TL072 altogether, pin 3 voltage is still 0.
power goes in at full voltage (8.4), measures 2v after the first 2.2M resistor, then the voltage drops to the culprit 0.98 on the jumper connecting that to pin 3.
You're going to have to go back to basics with the pin3 thing.
With the tl072 out of its socket, disconnect the cap feeding the junction of the two 2.2M ......& also disconnect the jumper feeding the junction onwards to pin 3, so basically all you are going to have left is this....
9V
|
2.2M resistor (top)
|
---->
voltage here should be approximately 4.5V|
2.2M resistor (bottom)
|
|
0V
if after doing the above you've still got 0V at the junction of those 2.2M resistors then you've a solder bridge or short somewhere or other.
okay, done those things - voltage going into the circuit is now 4.5, voltage at the junction is about 1V. it's just being illogical now. i'm thinking i should just cut the board in half and re-do both circuits separately.
cutting power to the LM386 brought the input back up to full voltage. didn't even touch anything near that side of the circuit. dunno if my mind's just totally fuzzy lately, there's one ultra-tiny solder bridge i just can't find, or if merging these circuits in the way i've done is just not feasible.
Quote from: MrStab on April 08, 2013, 10:14:25 AM
okay, done those things - voltage going into the circuit is now 4.5, voltage at the junction is about 1V. it's just being illogical now. i'm thinking i should just cut the board in half and re-do both circuits separately.
If you've the circuit as outlined in my last post yet still are seeing just 1V at the junction, it can only mean three things...
1. You resistors aren't the values you think they are (but they look fine in the photo - so I doubt it)
2. There's still something else connected to the track that those two resistors join.
3. The device (or person!) doing the measuring isn't working properly!!
Essentially you've a basic two resistor potential divider that has the wrong (unexpected) voltage in the middle ...if you are feeding it 4.5V into two equal resistors ...you should be seeing 2.25V at the junction.
edit: Just seen your latest post - it's still not clear - are you now saying that after removing the LM386 the resistor junction voltage is now reading half the supply voltage correctly? (if so see 'possible problem' No2 above)
upon audio probing, the signal passes right through the buffer stage as it should, ofc that probably doesn't guarantee successful buffering. or does it..? lol
i'll try to clear things up: for some reason, the input voltage dropped to 4.5, so i cut the jumper taking the battery voltage straight to the LM386, and input voltage returned to full ~8v (due a replacement battery...). can probably ignore that part for now, though.
so, assuming full, unadulterated input voltage, pins 1 & 2 are back at 4.5 (or dying battery equivalent), and the junction and pin 3 are still 2v. i don't understand how the voltage is being halved properly elsewhere but not pin 3 or at the junction itself. cannot find any shorts at all! even cutting between strips with a stanley knife for the sake of it. *sigh*
Quote from: MrStab on April 08, 2013, 11:07:10 AM
upon audio probing, the signal passes right through the buffer stage as it should, ofc that probably doesn't guarantee successful buffering. or does it..? lol
i'll try to clear things up: for some reason, the input voltage dropped to 4.5, so i cut the jumper taking the battery voltage straight to the LM386, and input voltage returned to full ~8v (due a replacement battery...). can probably ignore that part for now, though.
so, assuming full, unadulterated input voltage, pins 1 & 2 are back at 4.5 (or dying battery equivalent), and the junction and pin 3 are still 2v. i don't understand how the voltage is being halved properly elsewhere but not pin 3 or at the junction itself. cannot find any shorts at all! even cutting between strips with a stanley knife for the sake of it. *sigh*
You are overcomplicating...forget about the LM386 for now (take it out of cct too!) - your input tl072 buffer will not work unless it's biased properly.
That's the job of the 2 x 2.2M resistors, but clearly you have a problem (refer to possible reasons in my last post) ...there should be half whatever your supply voltage is at the junction of the two resistors....if there's not, you've a problem & until you sort it, I wouldn 't waste anytime/energy trying to second guess whether your LM386 is affecting the circuit or not ... just like a house, you have to build up from solid foundations, & until you get the TL072 working...your house is shakey!
There's only two components (resistors) in play here - it really doesn't get any simpler! (actually, ok I relent....a one component circuit would be simpler :icon_mrgreen:!)
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.
hope this helps - not trying to teach grandma to suck eggs.
(http://upload.wikimedia.org/wikipedia/commons/d/db/Resistive_divider.png)
Quote from: MrStab on April 08, 2013, 02:54:33 PM
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.
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.
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.
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. :P
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
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"?
ahhh i see...more ''famous grouse'' i think.. :P
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
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.
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!)
1M resistors bring the junction/pin 3 to ~2.9V
tested resistance whilst in the circuit, both add up to 2M
Quote from: MrStab on April 08, 2013, 10:32:26 PM
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?
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?
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
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!
Quote from: MrStab on April 09, 2013, 09:55:48 AM
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!
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!
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*
'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. :icon_cool:
never trust a maplin goon. (no offence to any maplin employees who may be reading) they just pick parts from a labelled draw. have you checked your resistors with your multimeter? how many bands to the colour code? check under good strong white light to confirm value with online calc if no multimeter.
*edit* only just spotted your photo on page two - red, red, black, yellow, brown - 2.2MΩ 1% Warning: Non-standard 1% (E96) value. Standard E24 value. Reverse: 14kΩ(2%) reverse as in brown, yellow, black, red, red. from: http://www.hobby-hour.com/electronics/resistorcalculator.php
?
grant is colour blind IIRC...
sometimes that red can look brown in certain light to me too..
i despise Maplin with a passion! lol. they're the biggest joke of a company in existence. i just happen to have a bunch of 1M's from there, but the 2.2M resistors i have are from a fairly-popular UK retailer for pedal parts and i wouldn't like to discredit them as they've been great with everything so far. i can't imagine i would've gotten unlucky twice from different sources, when i've used parts from the latter to successfully build much more complex boards.
the schematic as it stands in my desperation is just 2 resistors soldered together with a 9V battery clip hooked up to either end. can't get more basic than that!
thanks for tolerating me here lol
please excuse my not-so-great camera yet again
1M resistors (from Craplin):
(http://i.imgur.com/SXKOg73.jpg)
2.2M resistors (from online):
(http://i.imgur.com/AmelBNF.jpg)
Battery test:
(http://i.imgur.com/tl0cS58.jpg)
Since you've got the most basic voltage divider in play....
1. connect 9V across these two identical resistors - note down the voltage at the junction.
2. Also, note down the battery voltage whilst the battery is physically connected to the same two resistors (you've already measured it @9.73V but that was with no strain on it)
3. reverse the battery wires to the same resistors (i.e. put the battery black wire where the red wire was & the red wire where the black wire was) - again, note down the voltage at the resistor junction
The above test should tell us something about the relationship of the value of the resistors
(I'm beginning to think your multimeter is loading this most basic of circuits down.....indeed if you get the same voltage reading at the junction for the tests above, that's the likeliest problem)
FWIW ....IMHO you should only be using Alakaline batteries....not zinc chloride from poundstretcher!
had a wee laugh out loud moment at the poundstretchers comment - however did you guess? :D i'm kinda broke. in my defence, i favour less-cheapskate batteries in stage applications. that's not really a defence at all. lol
tried a Duracell out of my wah at some point, just to rule out the battery causing wrong voltage.
right! so i understand direction #3 and i think #2 (basically test from the battery terminals whilst resistors connected?), but i don't get what you mean by #1? haven't i already done that in the pics, or do you mean something else?
i can only think of it being the multimeter, too - yet i used it to confirm PT2399 voltages just the other day. maybe there's some nuance at play which i don't understand.
it's quite inconvenient that "Voltage Divider" makes for a potentially-dangerous acronym.
Quote from: MrStab on April 11, 2013, 11:00:45 AM
right! so i understand direction #3 and i think #2 (basically test from the battery terminals whilst resistors connected?), but i don't get what you mean by #1? haven't i already done that in the pics, or do you mean something else?
Yes you've done it (but I didn't know which resistors you'd choose!), so again...
1. connect 9V across these two identical resistors -
note down the voltage at the junction (yes, you've done this once, butr we need to be scientific here!)
2. Also, note down the battery voltage whilst the battery is physically connected to the same two resistors (you've already measured it @9.73V but that was with no strain on it...so you need to also test the battery voltage when 'loaded' with the two resistors connected)
3. NOW
reverse the battery wires to the same resistors (i.e. put the battery black wire where the red wire was & the red wire where the black wire was) - again, note down the voltage at the resistor junction
Don't over think this...just carry out the above tests explicitly & report back!
2.31-2.32 V (slight fluctuation) with positive & ground at EITHER side.
9.72 @ battery with load.
overthinking tangent: if it is the multimeter, and the 4.5 reading at the at the output on pin 1 (& inverted input via. jumper) did suggest correct biasing, why might the "raw" circuit be loaded down, but not post-opamp?
Quote from: MrStab on April 11, 2013, 11:38:49 AM
2.31-2.32 V (slight fluctuation) with positive & ground at EITHER side.
9.72 @ battery with load.
Well that proves the resistors are of equal value (and you haven't a bad 'un in there)......I reckon you've not only bought nasty poundstretcher batteries, but also a nasty poundstretcher multimeter! (or equivalent)....false economy - look how much time you've wasted for the sake of an extra fiver!
Quote from: MrStab on April 11, 2013, 11:38:49 AM
overthinking tangent: if it is the multimeter, and the 4.5 reading at the at the output on pin 1 (& inverted input via. jumper) did suggest correct biasing, why might the "raw" circuit be loaded down, but not post-opamp?
because the junction of two high value resistors is very high impedance - easily loaded down by a poundstretcher multimeter, whereas the output of an opamp is very low impedance....even a sh1t Chinese sources poundstretcher multimeter won't makes it's voltage output waiver! You are right though...knowing what we know now, the opamp biasing was fine, but your pin measurements were very askew (due to your multimeter), which made it look like there was something seriously amiss with the opamp.
remember this...
Quote from: Gurner on April 08, 2013, 10:34:50 AM
If you've the circuit as outlined in my last post yet still are seeing just 1V at the junction, it can only mean three things...
1. You resistors aren't the values you think they are (but they look fine in the photo - so I doubt it)
2. There's still something else connected to the track that those two resistors join.
3. The device (or person!) doing the measuring isn't working properly!!
To give this mini peculiar diversion some closure, it was reason number 3!
hey, i'll have you know this multimeter cost me £6! lol
good to know that it's not ideal, especially given that i bought it to bias an amp in the first place... why do i smell burning...
i've only been at this pedal-building lark since mid-february and this is the first issue i've run into with it (or so i think), so i didn't think i'd get far enough to warrant a better one.
right, so after this unmitigated disaster, next time i run into dough i need A. a better multimeter and B. a bulk supply of decent batteries. it wasn't so much a case of saving an extra fiver as not having an extra fiver!
i'm gonna get back to work on this project, hoping i don't burn out my last LM386 (no output when i audio probed one of the 2 burnt ones), and to get this thread back on track i'll let you guys know how it goes.
thanks a lot for helping me figure it out! makes a lot of sense that it's the multimeter.
FWIW a decent multimeter needn't cost the earth...I have a reasonably priced & spec'ed Uni-T UT61E multimeter (Unit-T are a respected brand), which cost about £35 on Ebay, but their range starts much cheaper, for example...
http://www.ebay.co.uk/itm/UNI-T-UT-33B-LCD-Palm-Multimeter-Ohm-Volt-meter-UT33B-/330744556929?pt=UK_Mobile_Phones_Communication_Radio_Meters&hash=item4d01e96d81
bookmarked, cheers! i was a bit of a fish out of water when hunting for one, always been more of a computer nerd until recently. all i knew was i needed a 200mV resolution at the time. the irony was i rejected a few of the ones i looked at because they seemed a bit too flimsy. i can probably do without a transistor testing function for the time being.
Perfectly decent multimeters can produce similar results in that situation. It's one of those things you learn to watch out for, Gurner's little test is a useful check. You can do the same thing it a circuit, where you wouldn't want to reverse the battery by measuring from the junction to ground and then from the junction to the supply voltage. Courtesy of Gus Smalley.
Quote from: slacker on April 11, 2013, 12:38:06 PM
Perfectly decent multimeters can produce similar results in that situation.
I've just tried this same test with 2 x 1M resistors with my multimeter.
Battery voltage ....8.5V (loaded), junction voltage 4.182V (ideally, this should be measuring 4.25V, but it's close enough that in a troubleshooting scenario I wouldn't be knocked off course with a seemingly out of whack reading) ....but yes, Ian makes a good point .....even with a reasonably spec'ed meter there'll inevitably be a degree of loading/impact wrt high resistances ...just one of those things (but can be negated a fair bit by sticking with a reasonably trusted multimeter brand)
i'd much rather have 4.something than half what it should be!
trying to absorb as much as i can, this'll make for handy knowledge in future. will try to score a multimeter by the end of next week.
as i'm the kind of impatient moron who's gonna keep trying stuff until then (not too "mandatory" a project, i have fun just putting this stuff together):
probing reveals that audio passes all the way through both IC's as intended, but the LEDs stay on permanently. assuming the obvious, i tried a 1k resistor after the 10uF gain cap on the LM386 to lessen the gain a bit, but still no. no overheating (yet), though! my limited knowledge tells me that maybe something's getting into the 386 that shouldn't. or would the buffer stage change the characteristics enough that i should maybe consider taking out the gain cap altogether? as Rob's original design (and its rip-offs across the web) seem to assume a pure guitar input. (i would just go ahead & try this but unable to right now & it'd be interesting to know why the buffer may or may not affect the power-amp/LED stage)
So back to the original circuit...this is a very inelegant circuit!
For a start, the voltage across the leds is gonna change over the fade life of the LEDs...so even if you biased them perfectly on a fresh battery, as soon as the battery voltage drops, the LEDs are gonna be incorrectly biased.
If you measure the voltage coming out of your LM386...you'll see it's about half your supply voltage....this is with no signal.
So even without a signal you've got about 4.5V (assuming a fresh 9V battery) DC present ...if you place an led & series limiting resistor across it - the LED always be on.
What colour LEDs are you using? (also measure the voltage across one of your LEDs when its on)
i'm currently only testing with 2 blue LEDs in series, as per your advice i'm not gonna try running 4 in series in the final thing - will no doubt need to experiment with parallel and/or red LEDs. i've since taken the electrolytic cap labelled C2 out of the circuit (what would've been the buffer output cap), in case that matters.
voltage at LM386 output reads 7.5 (although my DMM could be lying!), 5.6 after the current-limiting resistor (1k), 2.75 before the 2nd LED. i take it something's wrong there if it's not 4.5, or are you assuming the power to the 386 comes after the voltage divider? 9v+ feeds into the LM386 directly, i figured i should keep both "halves" separate in that regard.
is there any way to elegant-ise it?
Quote from: MrStab on April 11, 2013, 05:28:42 PM
i'm currently only testing with 2 blue LEDs in series, as per your advice i'm not gonna try running 4 in series in the final thing - will no doubt need to experiment with parallel and/or red LEDs. i've since taken the electrolytic cap labelled C2 out of the circuit (what would've been the buffer output cap), in case that matters.
voltage at LM386 output reads 7.5 (although my DMM could be lying!), 5.6 after the current-limiting resistor (1k), 2.75 before the 2nd LED. i take it something's wrong there if it's not 4.5, or are you assuming the power to the 386 comes after the voltage divider? 9v+ feeds into the LM386 directly, i figured i should keep both "halves" separate in that regard.
is there any way to elegant-ise it?
Last question first ....IMHO ...no.
Can it be made to sort of work? Yes......but well? That depends on your expectations.
Ok, first problem, your LM386 output voltage is wrong (this is why your two blue leds are on all the time)...the LM386 output pin should be sitting at about 4.5V (half its supply voltage) - remove the LEDs and remeasure (btw the voltage here is low impedance so you can trust your multimeter!)
with all the haze of that earlier problem, I've sort of lost the plot a little & perhaps it's worth you posting voltage for all you LM386 pins (it's not a chip I use much so it's probably better to let other chime in here)
LM386 WITH 2x blue LEDs connected:
3.54
0
4.59
0
7.48
8.17
9.14
2.01
WITHOUT LEDs:
3.58
0
4.62
0
7.76
8.38
9.22
2.01
i've wasted more than enough of your time, G - no worries if you wanna take some time out!
i'm just surprised quite a lot of people seem to have tried the 386-LED thing with no regard for tone suck. is it an inherently problematic concept, or only so with the buffer in front?
pin 3 should not be at 4.59V...you need a cap between your tl072 output & the LM386 input (I've just gone cross eyed trying to follow your board layout & mapping it into a schem in my head!)
you'll also need a pull down resistor to ground on the right hand side of the cap (LM386 side)...something like 10k ought to be ok.
Try those things & see if your LM386 output returns to a more normal 4.5V(ish)
Re tone suck...I guess those who make the circuit are so won over by lights that they overlook the impact on their tone!
the way i see it, if anything superficial were to harm my tone, then it can GTFO! lol.
sorry, been busy the past day or so. built one of them Tube Reamers to take a break (awaiting aural reviews on whether i screwed it up or not!). anyways, back to work!
so restore the buffer's 10uF output cap with a 10k resistor immediately after? there appears to be space on the board made by fate for this very occasion.
next time i'll come up with a schematic on request instead of saying "that one joined to that one!" lol. my bad.
put 10uf cap between buffer out & 386 in, and unsure exactly what you meant i tried a 10k to ground both after this cap & at the output cap (separately), in both instances the output is still around 7.2V. pin 3 is down at 0.01, though
what does it sound like? put the multimeter away for a moment. 386 is a little power amp designed to drive a load. do you have a speaker you could connect for a quick listen? an old pc speaker perhaps? is it working? what happens to the sound when i swap/remove/add components?
http://www.ti.com/lit/ds/symlink/lm386.pdf (http://www.ti.com/lit/ds/symlink/lm386.pdf)
http://tymkrs.tumblr.com/post/13831067585/on-reading-datasheets-lm386-page-1 (http://tymkrs.tumblr.com/post/13831067585/on-reading-datasheets-lm386-page-1)
i realise that your project is not sonic but sometimes just listening can provide some clues and offer ideas.
okay, so i'm such an unbelievable genius that i had V+ connected to pin 6 when it should've been 7. and i had read the pinout before this! damnit!
output voltage is now 4.4! input voltage nonexistent. LEDs stay dimly lit. tapping front of newly-reinstated 10uF buffer output cap makes them flash & fade.
i audio probed it prior to fixing the voltage pin & putting the 10uF cap back in, and got signal through, and i had tried with a speaker before but burned out a chip and i'm on my last lol.
in any case, the only problem now hopefully lies between the buffer output & 386 input!
pin 6 power. pin 7 bypass cap to ground.
*also* if you need to knock up a quick scheme online: http://www.digikey.com/schemeit (http://www.digikey.com/schemeit) - you don't have to register, just try it now and export image.
Grant apologies, I think I mapped your circuit wrong in my head - I think the cap was already in place (C2 on your board layout) ....this is where a schem really helps debug (yes I know you're only linking two elementary circuits, but nevertheless...it can get confusing)
Quote from: artifus on April 13, 2013, 12:12:26 PM
pin 6 power. pin 7 bypass cap to ground.
how'd you mean? so pin 7 would be connected anyway but via. the bypass pin & a cap? not sure i understand the purpose of the bypass pin then! lol.
getting a flash/fade when i tap the positive end of he buffer output cap seems promising, but say it does work if i take it out (voltage pretty much dies there & then), how would i go about fixing the 4.5v pin 3 voltage?
no worries, Gurner - i think maybe this cap is dead or too high a value maybe (?), but im gonna test with it reoved & jumpered after a wee coffee and a smoke
pin 7 bypass power with a large cap. it helps with ground junk. read the above links. the toymaker articles talk you thru the whole datasheet in plain english with comments and replies.
*i didn't intend that as rudely as it reads back, i'm tired - forgive me. the toymaker articles are quite an interesting read as they are written by someone starting from scratch and asking for help online. you may have to search for the other three pages if they aren't linked*
admittedly i did overlook the other link as i had read the datasheet & thought it'd be much of the same, but i'll have a look just now. cheers!
something i have learned recently is that you have to read the datasheet again. and again... and again... and again... and again... and... that those guys really knew what they were talking about but were definitely not paid by the word!
i must've screwed up a solder joint when i put the buffer output cap back in - the circuit now works! i haven't put the power cap in yet, still haven't read the article properly.
i was looking for a shop which had the most obvious sign in large letters the other day, and i passed right by it twice yet somehow managed to process all the names of other shops but not this one. so worringly i've had real-world parallels with this! lol
gonna put the recommended cap in & then try seeing if i can double the LEDs in parallel, i'll let you guys know how it goes
yay!
(i really needed a yay today - nice one)
whoooohoooooo.....
@#$%ng hell it works!!!..yay!!. ;D
now draw a schematic of what you have.....so others can do it too!.. ;)
i'll start work on a schematic once i've managed to sort out the bypass/cap thing, verified that the buffer actually prevents tone suck (just been using a patch lead from a guitar for the time being), and tested 4 blues in parallel.
do i have this right: you don't hook up pin 7 TO pin 6, but instead by putting a cap on pin 7 to ground, you put it into bypass "mode" and power goes in via. pin 6 instead?
Quote from: MrStab on April 13, 2013, 03:31:20 PM
do i have this right: you don't hook up pin 7 TO pin 6, but instead by putting a cap on pin 7 to ground, you put it into bypass "mode" and power goes in via. pin 6 instead?
(http://www.beavisaudio.com/library/LM386/LM386_Datasheet_Example.jpg)
+9v to pin 6. 10uf (or bigger) cap from pin 7 to ground for good measure but not necessary. look at the internal 386 schematic on the datasheet and reread the notes. there is no bypass mode, the cap on pin 7 bypasses an internal resistor, stabilising a voltage divider.
http://www.electrosmash.com/lm386-analysis (http://www.electrosmash.com/lm386-analysis)
that's actually the very diagram which made me ask what i did. when i said "bypass", i didn't mean what's usually meant round these parts - i meant bypassing that pin for power supply.
i have it working, albeit without the above changes - for some reason that didn't work. it's all routed inside the guitar but the circuit is easy to get to, works quite well actually! just need to try to squeeze out as much brightness as i feasibly can & fix the power supply issue ofc
here's my dilemma: while i don't doubt for a second that i should be using pin 6 as outlined above, and it was most likely a small, mis-diagnosed error which made it not work for me when i tried it, it just works on pin 7! as the audio pretty much reaches a dead end, and everything seems in working order, wouldn't it be fine to leave it? so long as it's just me taking the risk? however, i don't wanna go putting a schematic out there with something potentially sketchy on it, so if i switch V+ to the proper config, someone else will have to verify it. i'll try to get a video later.
about switching:
using an SPDT switch (well, half of a DPDT), this is how i managed to keep the lights off when the circuit was off (as predictably they stay on if not grounded):
(http://i.imgur.com/ez67Sm1.png)
all good? while sound seems more or less fine for the POS guitar i tested this in (has a minor grounding problem to begin with), i wouldn't be satisfied without a full A/B comparison so i'd need to find a way to sever the power if possible. or i could just pull out the battery when playing...
potential problems (may have been mentioned elsewhere): to what extent could a dying battery impact tone-suck-prevention? two batteries is a solution, but that's just excessive. i think that's even the punchline of a joke i once heard. also, turning on & off makes a little high-pitched squeak, not too obnoxious but it's there. not toooo bright using 1k resistors on the LEDs, but could probably improve that by positioning them better and you probably don't wanna risk retinal damage from this, of all things. lol
can't think of anything else for now.
i'm by no means an expert on the 386, i've just tinkered a bit.
the oddest and only non standard lm386 configuration i've seen so far is here:
(http://www.next.gr/uploads/135-10323.png)
i've no idea what's going on with pin 6 here. i get the pin 8 to ground oscillator bit (it was listed as a tremolo) but the input and power arrangement is a mystery to me.
as to your tone suckage - i haven't really looked at your circuit, a schematic would help, but i would look at the buffer and how the signal is split for clues. also, decoupling - maybe try two 10 - 100 ohm resistors between +9v and the power inputs to the two chips with a large cap across each to ground. apologies if this has already been suggested and tried.
(illogical post, since modified)
i've just built the circuit with just the 386 side, and pin 6 works but pin 7 doesn't. weird! your diagram gives me hope for this Twilight Zone circuit, even if it's not the same kind of weirdness. lol
the tone suckage isn't conclusive as yet, could well be subjective. times like these i wish i had an oscilloscope (i volunteer at a charity music shop which has a bunch of oscs just gathering dust downstairs, but it would be sketchy to ask for a freebie!). duly noted on the decoupling - i don't think it's been suggested, but i'll give it a go if further testing necessitates it.
i'll draw up a schematic asap using the link you provided - assuming the tone suck is a non-issue, i'll draw it out with Pin 7 and put a note explaining the situation.
i'm finding it easier to learn about the 386 in applications, then going back to the datasheet.
i guess the question isn't why pin 7 accepts power, that seems fairly obvious, but the issue is why are the voltages all off when pin 6 is used... looking at the schematic of the 386 itself, wondering how the buffer stage might cause an issue. i suspect some short on my part, but what's really odd is that the voltages when i try to use pin 7 on the 386-only version of the circuit are similar to when i try to use pin 6 on the full thing.
the datasheet says max input voltage is ±0.4V, but if the output voltage from the buffer exceeds that, could it have any bearing...? maybe worth noting that it didn't work without the buffer output cap.