lm386 pin doubts

[daceb]

I just wanted to know how the gain pins, 1 and 8, work... how come a capacitor helps you to control said gain? Also, does this amp include a low pass filter, or is the usual audio configuration used for the voice filtering

 

[AllVol]

The LM386 data sheet, under the heading Gain Control, pretty much answers both questions.

 

[audioguru]

You can hear to 20kHz. If you use a lowpass filter then voices will be missing the high frequencies of consonants that are important for understanding speech (unless you are 100 years old and can no longer hear high audio frequencies).

The datasheet of the LM386 shows that when its gain is 20 (26dB) then its frequency response is flat to 100khz and is -3dB at 300kHz.
When its gain is 200 (46dB) then its frequency response is flat to 10khz and is -3dB at 30khz.

If you want to remove important high audio frequencies (and hiss) from speech then use an active lowpass filter circuit feeding the power amplifier.

 

[Roff]

I just wanted to know how the gain pins, 1 and 8, work... how come a capacitor helps you to control said gain?

There is an internal resistor between pins 1 and 8. If that resistor is in the circuit, the gain is 20. If that resistor is bypassed (AC short circuit) by a capacitor, the gain is 200. If you need to know how resistors can determine gain, you would have to understand feedback theory. If you don't know that the impedance of a capacitor goes down as frequency goes up, do a search for "capacitive reactance". If nothing makes sense, take it on faith and start studying.