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little amp


cr_XD
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hi dudes, i built this little thing: lm386 amp

and it works perfectly when i plug in my mp3 player. B)

but when i plug in my guitars, may it be the electric or the acoustic, i can't hear anything :D

could it be something concerning impedance, cos i ain't got a clue ¡ :D

i would apreciate any input

bye

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Absolutely nothing or very soft? Absolutely nothing would indicate a disconnect between guitar and amp.

What type of plugs and sockets are you using? An MP3 player would give stereo out on a stereo jack plug which is probably why you are hearing one channel into your amp. Have you used a mono or stereo plug into your amp?

Keith

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i cheked the cables and conexions and they were all working, the mp3 i plug it through a mono plug (dunno if matters) and both guitars sound through my working amp.

about the signal volume... well this has lead me to doubts, cos i can't really hear nothing, but maybe it is amplifying really really softly. anyhow i don't think this may happen with the acoustic as it has a preamp and i've tried turning it full volume.

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it has enough gain for mine.. loose the cap and add a 1k pot for a better gain control the input pot is an input resisotr to keep it from overloading it with a hot signal the actual gain is in between the pins one and eight. otherwise i would try to flip the cap in the feedback loop there the polarity is backwards compared to every other schematic i have found on the net. personally if you go with the cap there you can just bridge the pins together there same effect.

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what kind of pickups do you have.. if you are under 3k then it probally doestn' have enough signal gain to drive it.. if your pickups have more output than 3k then it i will drive it enough to mild clip it at max gain settings.. of course it also depends on your input and output caps.. i use a .068uf in and a 1uf out. and mine functions perfectly well as a distoriton box and an amp.

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any thing over 1.35k in between pins 1 and 8 is over kill. internal resistance between those pins is 1.35k fixed resistor. you can take a 2k jpot and put a resistor in there. or just use a 1k pot

using a 5k will give you nothing until you get around the 2/3 mark

http://www.national.com/ds.cgi/LM/LM386.pdf

1st page half way down

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Resistors in parallel follow this rule:

1/Rx=1/R1+1/R2 (etc.)

1/1350+1/5000 = .00074 + .0002 = .00094

(feel free to check my math - my calculator isn't working)

So Rx = 1/.00094 = 1.063K

So you've boosted the gain just by inserting the 5K pot, right? Even at its lowest setting? And any further change in the setting of the pot will boost gain further, correct? So the pot works as a master volume, going from slightly over 20 (at the 5K point) to the full rated 200 ( at the other end of the range, 0 ohms). I don't see the problem. The smaller pot would simply give you less variation in gain by setting the minimum gain to a higher point. With this setup, you should be able to set the gain for a clean sound if you want it. Of course, my whole point was to show the FET buffer stage to boost the signal so it would drive the amp. :D Thanks for the spec sheet, there's a couple of interesting ideas in the App notes.

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yeah you would think that basic principles would hold true. but for some reason, which has baffled me since i tried it every multimeter stil shows 5k on pot and 1.35k across chip. don't understand why. i thought it was my mulit meter. but i got a new one and it still says same. but if get same value resistors and parrallel them i get what you said, which is what i should, hmm maybe i got a bad batch of chips.

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but for some reason, which has baffled me since i tried it every multimeter stil shows 5k on pot and 1.35k across chip. don't understand why.

Are you saying that you took both these measurements while the pot was connected to the chip? If so, there's no way that you can have two different readings on two components connected in parallel unless you have a bad connection somewhere (bad solder joint, broken wire).

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i checked that too.. i think the pin legs on the chip isn't made very well the recent ones i have used are from a different distributor

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... "little" is the key word just put some more wattage into that little thingy

We probably ought to start a new thread for this, but how much wattage do you need? This circuit isn't loud enough to gig with, but it'll certainly get loud enough (with a good speaker) to irritate your friends and neighbors. :D

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http://www.geocities.com/austenfantanio/an...silmarshall.htm

ms2 mods to give more wattage pushing a 4*12 cabinet.. aprox 4 watts

http://www.geocities.com/austenfantanio/ro...abtypethang.htm

aprox 2 watt rotocab vibrato thing

http://www.geocities.com/austenfantanio/Hybrid.htm

hybrid small amp clone

i have a few more pics but not sure what i have deon with them.

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lol. i'm sorry i haven't been around here for a time, and i'm happy to see so much interest, see if tomorrow i can write a little more about the schematics you've posted, but i think the main problem was the signal level from the pickups, i will try and put a npn preamp before the chip.

i'm going back to study..... :D ..... tomorrow is my last exam, so i will have some time to fool around with the solder XD

thanx

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