Distortion In LM386 Amplifier

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I have an amplifier in my workshop, for listening to tunes from my
iPod, but if I turn it up louder then whisper level, it distorts,
pretty bad.  I've been going nuts trying to figure it out, even tried
many different speakers, from 1/2 watt to 20 watt ratings, and swapped
out the LM386 chip. I have another one of these kits, used for an iPod
amp around the house played through a 1 watt 2 inch speaker, plays
fine, with little or no distortion at normal listening levels. This
amp is run off 4 AA batteries, while the distorting one is run of a 9
volt battery.


Schematic:
(Look at the amplifier section)

http://www.siliconchip.com.au/cms/gallery/article.html?slideshow=0&a10%1845&i=3


Re: Distortion In LM386 Amplifier



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I got a 404 error.

It may be oscillating.  The datasheets usually show a resistor and
capacitor in series, connected from the 386 output to ground.  This is
to deal with oscillation, and if it's missing there may be problems.

Likewise, if the input gets too close to the output, it may go into
oscillation.

Those things are decades old, and really there isn't much that can
go wrong.  So unless the specific IC is somehow bad, it can supply
decent albeit small amounts of sound.  It is possible to overload it,
but since you should have a volume control acting as a variable
voltage divider at the input, that's not going to be a problem.

Layout may also be an issue.  If there's not good wiring to the power
supply, the resistance of the wires may become a factor and that can
start causing problems.

    Michael

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That schematic shows a 12 volt power supply, but you say you
are using a 9 volt supply.  The LM386 draws significant
current pulses from its supply. Is it possible that your
supply is bouncing around in the presence of these pulses?
If you are using a 9 volt battery, you might try paralleling
it with a few thousand microfarads of capacitor.

Oh, I almost forgot.  That schematic shows no way for the
LM386 to be connected to the speaker. RLY1 either leaves it
unconnected to any load except for the RC filter, or to the
output of a 555 timer and a terminal called "line".
Something very wrong there.  Or is all that not part of your
system?

--
Regards,

John Popelish

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No, I'm only using the amplifier, I linked to that page, as I've lost
the schematic that came with the set. Ignore the rest of the circuitry

Dave
Australia

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I've tried the amp on 3 AA batteries, and tidied the wiring to the
battery, no success, I have yet to try the capacitor, but I don't
think it's anything to do with the battery supply. Maybe the 220 uF
cap on the output has gone? I haven't had much experience
troubleshooting electronics
Dave
Australia

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A bad output capacitor will certainly make the audio sound
bad (thin and distorted).  Do you have a second one to try?

--
Regards,

John Popelish

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Yeah, replaced that cap, sound is undistorted at normal listening
levels now through a 4 inch, 1 watt 8 ohm speaker ripped out of a
1980's radio cassette, I was going to replace that cap before I posted
the original message, but thought I'd get the advice from more advance
hobbyists first.

Dave
Australia.

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Another thing I've noticed with this amp, and the iPod amp I built for
my father (different amplifier circuit) is that every now and then I
hear a buzz through the speaker, This can get annoying when using the
amp for a long period.  I assume it's some kind of interference, what
could be causing this?  It happens every 2-5 minutes.

Dave
Australia

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Cell phone?  More likely if it is a modern digital one.

Re: Distortion In LM386 Amplifier


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Quite likely. Although I don't use one, several members of the
household leave theirs one day & night, and they are all modern
digital phones.

Dave
Australia

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possible, but the range of the interferance isn't very great though,
unless your circuit is spread out enough to act as an antenna.


Bye.
   Jasen




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your mobile phone.

Bye.
   Jasen

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"Dave.H" wrote:

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The fact that it's a crappy amp chip about 35+ yrs old probably has a LOT to do
with it.

The best thing National could do is accidentally destroy all the masks for it.

Graham


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 > The fact that it's a crappy amp chip about 35+ yrs old
probably has a LOT to do
 > with it.
 >
 > The best thing National could do is accidentally destroy
all the masks for it.

It may not be hi-fi, but its normal sound quality is not the
problem, here.

--
Regards,

John Popelish

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John Popelish wrote:

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Maybe so but I shudder whenever I see yet another audio project based
around one.

They are notoriously useless.

Graham


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Yes, and they are used where they fit.  A small bit of amplification in
a small package.  Nice and useful.  I can remember from before it
was released, and you were stuck with a bulkier package, and move
back a bit in time and you needed a lot more external components, and
move a bit further back in time, and you needed all kinds of discrete
components because there were no IC audio amplifiers.

The fact that some use it where it's inappropriate, trying to get
more power than it can offer or demanding something else from it
that it can't supply, is not the fault of the IC.  A lot of those
uses, they'd likely be junk even if some other audio amplifier
IC was used.

    Michael


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