Lm386 Amp Circuit Fail.... - Page 1
Forum section: electronics / beginners

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 29, 2013, 07:43:43 pm
content: Today after a lot of tests i decided to build my own Lm386 audio amp to use it for portable music and bass guitar amplification.I got it done and when i tried to power it up it would not turn on.After a good inspection i found a solder bridge which i then sucked the solder from with some solder wick.But after that i could only hear the music pretty low on volume (even with the volume full at my cell and my potentiometer at its lowest resistance).So i inspected it again and nothing...Please help me i really need to get it working.It is based on this schematic :http://hackaweek.com/hacks/wp-content/uploads/2011/04/LM386ampschematicfinal.jpgThe videoAnd It worked perfectly on breadboard.......There are some photos from my project (as high resolution as i could get with my webcam)http://imageshack.us/g/198/picture1tt.jpg/They are 8 Pics i will upload more with details if you need please help me.thank you.

author: w2aew
author_rank: Super Contributor
timestamp: January 29, 2013, 11:11:28 pm
content: Its tough to diagnose your project with those pictures. But the obvious things to check are... Proper wiring of the pot (is it backwards)? Did you check with the pot at the other extreme? Another good possibility - the LM386 may have been damaged due to the solder bridge when powered up. Have you substituted another device?

author: Farley
author_rank: Regular Contributor
timestamp: January 30, 2013, 02:02:08 am
content: Assuming the wiring is correct, as w2aew stated, the solder bridge may have caused a problem with the IC. Do you remember what pins were bridged?Also, that .01uF coupling capacitor between the pot and pin 3 seems too small. Try a 2.2uF.I note on the schematic you linked that there is a note stating that leaving out the cap between pins 8 and 1 on the LM386 would result in "max gain." This is opposite of what the spec sheet indicates.Whenever I start using a new IC I usually start with one of the circuits from the manufacturer's spec sheet until I'm comfortable with how the part is behaving. Digesting and understanding the spec sheet is a great learning experience. At least it is for me.http://www.ti.com/lit/ds/symlink/lm386.pdf

author: nobody
author_rank: Newbie
timestamp: January 30, 2013, 08:45:15 am
content: Yesterday i maked lm386 amp but using thisand it was working, but i added 100uf and 47 nf ceramic capacitors for noise and i didnt use potentiometer. Long wire that you are using might give you extra noise

author: CarlG
author_rank: Regular Contributor
timestamp: January 30, 2013, 08:53:17 am
content: It doesn't work even if you replace the LM386 with a new one?

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 30, 2013, 02:46:16 pm
content: The problem is not the noise .... i will show you pics with the components and the wiring and a video of me wiring it so that you can if something is wrong.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 30, 2013, 02:47:07 pm
content: I also changed the ic and it doesnt do any better.

author: CarlG
author_rank: Regular Contributor
timestamp: January 30, 2013, 08:33:44 pm
content: OK, then I guess we can rule out defect LM386. The design is so simple that it would be hard get it wrong, and you had the same ciruit working before, so...I would take another real good look at where that solder bridge was. Or, you may not even need to do that, just scratch with a scalpel, a needle or some other small tool, between the pins or wherever the bridge was. There might be some small piece of solder left, virtually invisible for the naked eye, shorting something.If that doesn't work, check that you really got the wiring right.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 31, 2013, 05:59:05 am
content: i will do thank you.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: January 31, 2013, 07:12:18 pm
content: Thank you all guys really.The problem was my idiocyI confused the pin 6 with the pin 7 of the chip so i got the connection wrong.Thank you again.