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LM386 Fried my i Pod

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I tried to make an audio amplifier using the LM386 amplifier ic (wired for x200 gain) only I added some resistors to bring up the voltage for the input (a 10k to the power, and a 1k to the ground) to try to overcome the 0.7 voltage drop of the input. I am using a 12V power supply, and when I pluged my i Pod in I saw a spark and smelled something burning:eek:, so i unpluged it, the i Pod still works (bareley), but now the left head phone is louder and gets hot after a while. I think that I know what went wrong, but if you could please help me look for a place that can fix it (preferably by mail), and also look at my circuit, because it did not work too well either, even before the sparks. If it realy was x200 gain then I temprarily lost most of my hearing during the project. the only part that I left out in the circuit was the 10k pot on the input, but I did not see it to be nesccary. WHY WOULD MY BELOVED ELECTRONICS BETRAY ME?!?!?!?!:eek:

a link to the LM386 data sheet:
https://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS006976.PDF

images of the circuit and pinout:
9244-lm386-200.gif

 
Last edited:

Shax

Member
Sounds like you connected your ipod to a potential divider, and not as shown in the application note diagram... 0/10 :D
 

audioguru

Well-Known Member
Most Helpful Member
The input of the LM386 amplifier is not 0.7V. It is 0VDC.

I don't know why you made a voltage divider with a 10k resistor to +12V and a 1k resistor to ground at the input which applied +1.09V to the output of your ipod.
But I think you applied +12v to the output of your ipod.

The output of an ipod is plenty to drive an LM386 that has a gain of 20. A gain of 200 is much too high and is used with a microphone as an input device.
 

transistor495

Member
Forum Supporter
I added some resistors to bring up the voltage for the input (a 10k to the power, and a 1k to the ground) to try to overcome the 0.7 voltage drop of the input. I am using a 12V power supply, and when I pluged my i Pod in I saw a spark and smelled something burning:eek:,

This looks suspicious, and you obviously supplied the power line to iPod output and it might have burned well a corner of iPod IC..:)
 

JimB

Super Moderator
Most Helpful Member
Looks like the OP gained some good experience here, see my signature line.

JimB
 
The input of the LM386 amplifier is not 0.7V. It is 0VDC.

I don't know why you made a voltage divider with a 10k resistor to +12V and a 1k resistor to ground at the input which applied +1.09V to the output of your ipod.
But I think you applied +12v to the output of your ipod.

The output of an ipod is plenty to drive an LM386 that has a gain of 20. A gain of 200 is much too high and is used with a microphone as an input device.

I was told that the input needed to be raised above 0.7 volts to accommodate the inevitable voltage drop of the input, is this correct or not?:( Should I add an isolation capacitor to the input to try to prevent future shorts?
 

transistor495

Member
Forum Supporter
the only part that I left out in the circuit was the 10k pot on the input, but I did not see it to be nesccary.
You left out the necessary 10K and tried some strange experiments over there:D

I've added a picture for connecting single channel to the mono amplifier LM386. 10uF not necessary as the minimum gain is OK for iPod output level.

If necessary, you can add a mixer in between for inputting the stereo frequencies.
My iPod audio amp:)
 

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schmitt trigger

Well-Known Member
From the data sheet, page 1, start of 2nd paragraph:

"The inputs are ground referenced....."

Unfortunately, you commited one of the most common errors: you did not read the data sheet thoroughly. I know reading datasheets is a drag, but it is a must if accidents like these are to be avoided.
 

audioguru

Well-Known Member
Most Helpful Member
Both inputs of an LM386 are at 0VDC.
The input signal makes one input swing slightly above 0V and slightly below 0V.
An input coupling capacitor is needed when the signal source has a DC voltage on it.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
... my electronics teacher...

I don't know what he is, but he's certainly NOT an electronics teacher.

If it's anything like in UK schools, you take a random teacher (English, History - anything) and send him/her off for a days training course, they then become the school 'electronics' teacher.

I taught my daughter to solder when she was about 8 years old (took five minutes or so), at about 12 she did a small amount of electronics in school, and could solder better than anyone in the year, including the supposed teacher :p
 

audioguru

Well-Known Member
Most Helpful Member
I had some teachers who came straight off the boat and could not "speeky zee English". Nobody in my classes knew what they were saying but they also probably didn't know themselves.
 
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