cr_XD Posted February 5, 2004 Report Share Posted February 5, 2004 hi dudes, i built this little thing: lm386 amp and it works perfectly when i plug in my mp3 player. but when i plug in my guitars, may it be the electric or the acoustic, i can't hear anything could it be something concerning impedance, cos i ain't got a clue ¡ i would apreciate any input bye Quote Link to comment Share on other sites More sharing options...
KeithHowell Posted February 5, 2004 Report Share Posted February 5, 2004 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 Quote Link to comment Share on other sites More sharing options...
cr_XD Posted February 5, 2004 Author Report Share Posted February 5, 2004 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. Quote Link to comment Share on other sites More sharing options...
syxxstring Posted February 5, 2004 Report Share Posted February 5, 2004 There's not enough gain to drive your pickups try using a preamp of some sort like a distortion pedal. Quote Link to comment Share on other sites More sharing options...
ansil Posted February 5, 2004 Report Share Posted February 5, 2004 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. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 6, 2004 Report Share Posted February 6, 2004 Isn't the LM386 a power amp? If so, your pickups probably aren't hot enough to drive it without a preamp. Try syxxstring's suggestion - if it works, you'll just have to add a preamp. The output from your MP3 player should be line level, way higher than a guitar output. Quote Link to comment Share on other sites More sharing options...
ansil Posted February 6, 2004 Report Share Posted February 6, 2004 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. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 8, 2004 Report Share Posted February 8, 2004 Don't know if you've fixed your amp problems, but here's a LM386 based mini-amp that uses a JFET as a buffer: Ruby It's not that different to your original schematic. You should have no problem adapting your board to accomodate the few extra components. Hope that helps. Quote Link to comment Share on other sites More sharing options...
ansil Posted February 8, 2004 Report Share Posted February 8, 2004 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 Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 8, 2004 Report Share Posted February 8, 2004 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. Thanks for the spec sheet, there's a couple of interesting ideas in the App notes. Quote Link to comment Share on other sites More sharing options...
ansil Posted February 8, 2004 Report Share Posted February 8, 2004 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. Quote Link to comment Share on other sites More sharing options...
Saber Posted February 8, 2004 Report Share Posted February 8, 2004 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). Quote Link to comment Share on other sites More sharing options...
ansil Posted February 8, 2004 Report Share Posted February 8, 2004 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 Quote Link to comment Share on other sites More sharing options...
The REAL Nordic God Posted February 8, 2004 Report Share Posted February 8, 2004 i give you props for building an amp {wish i was that smart} but "little" is the key word just put some more wattage into that little thingy Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 9, 2004 Report Share Posted February 9, 2004 ... "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. Quote Link to comment Share on other sites More sharing options...
ansil Posted February 9, 2004 Report Share Posted February 9, 2004 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. Quote Link to comment Share on other sites More sharing options...
cr_XD Posted February 9, 2004 Author Report Share Posted February 9, 2004 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..... ..... tomorrow is my last exam, so i will have some time to fool around with the solder XD thanx Quote Link to comment Share on other sites More sharing options...
cr_XD Posted February 10, 2004 Author Report Share Posted February 10, 2004 done, finished at last....... time for and so, i´m building ruby in a new board but recycling most of the components. i´ll probably make photos and mp3's when i finish, thanx for all the input. Quote Link to comment Share on other sites More sharing options...
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