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Old 31st July 2012, 05:58 AM   #1
JamieB is offline JamieB  Australia
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Default Bypassing pin question

Hi,
I have just built my first stereo amplifier based on the typical applications circuits in the LM386 data sheets. It works very well so I'm happy.

However, the speakers I have it connected to sound a bit tinny and I want to compensate for the lack of bass so I'm looking at the bass boost circuit in the data sheet.

The data sheet refers to bypassing certain pins. Is this just a standard bypass running from the pin to a cap to ground? Also, I notice that the diagrams feature dotted lines running to a cap labelled "bypass". Is this standard practice for designating a bypass capacitor? I assume that a value of 0.1uF is a good value to use here?

Cheers,
JamieB
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Old 31st July 2012, 08:07 AM   #2
Mooly is online now Mooly  United Kingdom
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Hmm... the LM386. That's an oldie

For good bass response the speaker coupling cap needs to be large enough. That depends on the speaker impedance but 250uf and 8 ohm has a -3db point of around 80hz. So something of the order of 2200uf would be better.

The bypass pin (pin 7) I would have though would be decoupled with something around 10uf to ground.

The big problem with all these older IC's is that although they seem ultra simple to use they can in reality be prone to oscillation and instability. Layout has much to do with that. I would always recommend using a scope to check for stability. Manufacturers data sheets often show alternative parts as dotted. You have to remember these are typical applications rather than fully worked projects.
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Old 31st July 2012, 08:26 AM   #3
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There is a bass boost schematic on the datasheet. However with so low power, less than 1Watt, I doubt u will get anything. Go for some higher power ICs like TDA2003. And I hope your speakers are in a cabinet.

Gajanan Phadte
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