Author Topic: lm386 amp on a breadboard - oscillation  (Read 2724 times)

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lm386 amp on a breadboard - oscillation
« on: February 02, 2014, 10:20:56 pm »
Hi

Is it even possible to make an amp on a breadboard that doesn't oscillate? I had an LM386 kicking around, so I thought it would be amusing to wire it up, listen to some music while I play. I made the 'minimum parts count' layout from the data sheet, which has a 250uF cap in series with the speaker, and a 50nF cap/10R resistor in series to ground (from the output).

It buzzed horribly to start with, but I twisted the speaker wires together and put a 100uF cap in parallel with a 10nF cap directly across the power supply pins. Now no buzz, but it oscillates at 690kHz. Sounds kind of OK, and doesn't draw a huge amount of current (20-30mA), but it would be nice if it didn't oscillate!

Any ideas how I can tame it?

Many thanks
John
 

Offline Rerouter

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Re: lm386 amp on a breadboard - oscillation
« Reply #1 on: February 03, 2014, 03:23:16 am »
10nF cap between inverting feedback pin and output pin,
 

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Re: lm386 amp on a breadboard - oscillation
« Reply #2 on: February 03, 2014, 08:21:25 am »
Thanks, I'll give that a go.

John
 

Offline blackdog

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Re: lm386 amp on a breadboard - oscillation
« Reply #3 on: February 03, 2014, 11:50:57 am »
Hi Icon, :-)


Do not forget to use a capacitor from pin7 to ground, say 10uF (Bypass).
And the zobel network on the output, 10-Ohm and 47nF on pin-5 (output)
It is all in the datasheet, firtst page.

Minimum components circuits is asking for troubles  :-DD

Kind regarts,
Blackdog
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

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Re: lm386 amp on a breadboard - oscillation
« Reply #4 on: February 03, 2014, 08:56:54 pm »
The bypass capacitor on pin 7 seems to have mostly done it - still a very slight wobble at ~700KHz, but there's too many wires trailing around...

Thanks
John
 


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