Distortion In LM386 Amplifier

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

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?

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Regards,

John Popelish

=3D...

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

=3D...

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

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

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

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Regards,

John Popelish

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

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Regards,

John Popelish

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.

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

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

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

They are notoriously useless.

Graham

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

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

your mobile phone.

Bye. Jasen

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