Lm386 - Electronic Circuits Projects Diagrams Free

epilot · 22nd February 2007, 09:17 AM

Hi,

As you know LM386 IC is a power amplifier.
Why there is a Filter at the output of it when it is used as Radio amplifier?

dch222 · 22nd February 2007, 10:08 AM

Its a low pass filter so I can only think its there to reduce any residual RF or HF signals above audio range which may damage the speaker or cause unwanted modulation effects.

Only guessing though.

johankj · 22nd February 2007, 10:15 AM

It's been a while since I've done LRC, but that looks like a band-pass filter.

AllVol · 22nd February 2007, 10:52 AM

The data sheet indicates it is for bass boost. Note also that the inputs are reversed from the typical amplifier circuits also shown on the data sheet.

stevez · 22nd February 2007, 10:53 AM

A guess on my part - possibly a way to prevent oscillation at high frequencies.

audioguru · 22nd February 2007, 03:27 PM

Look at the datasheet for the LM386. At the frequencies of the AM broadcast band and the 455kHz IF frequency of an AM radio the LM386 has lots of gain. The speaker and its wires will spray the amplified signal all over the radio causing it to oscillate if the lowpass filter isn't there.

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22nd February 2007, 10:08 AM	(permalink)
dch222	Its a low pass filter so I can only think its there to reduce any residual RF or HF signals above audio range which may damage the speaker or cause unwanted modulation effects. Only guessing though.

22nd February 2007, 10:15 AM	(permalink)
johankj	It's been a while since I've done LRC, but that looks like a band-pass filter.

22nd February 2007, 10:52 AM	(permalink)
AllVol	The data sheet indicates it is for bass boost. Note also that the inputs are reversed from the typical amplifier circuits also shown on the data sheet. __________________ All those who believe in psycho kinesis, raise my hand.

22nd February 2007, 10:53 AM	(permalink)
stevez	A guess on my part - possibly a way to prevent oscillation at high frequencies. __________________ stevez

22nd February 2007, 03:27 PM	(permalink)
audioguru	Look at the datasheet for the LM386. At the frequencies of the AM broadcast band and the 455kHz IF frequency of an AM radio the LM386 has lots of gain. The speaker and its wires will spray the amplified signal all over the radio causing it to oscillate if the lowpass filter isn't there. __________________ Uncle $crooge