GAIN CONTROL
To make the LM386 a more versatile amplifier two pins (1
and 8) are provided for gain control With pins 1 and 8 open
the 1 35 kX resistor sets the gain at 20 (26 dB) If a capacitor is put from pin 1 to 8 bypassing the 1 35 kX resistor the
gain will go up to 200 (46 dB) If a resistor is placed in series
with the capacitor the gain can be set to any value from 20
to 200 Gain control can also be done by capacitively coupling a resistor (or FET) from pin 1 to ground
Additional external components can be placed in parallel
with the internal feedback resistors to tailor the gain and
frequency response for individual applications For example
we can compensate poor speaker bass response by frequency shaping the feedback path This is done with a series RC from pin 1 to 5 (paralleling the internal 15 kX resistor) For 6 dB effective bass boost R j 15 kX the lowest
value for good stable operation is R e 10 kX if pin 8 is
open If pins 1 and 8 are bypassed then R as low as 2 kX
can be used This restriction is because the amplifier is only
compensated for closed-loop gains greater than 9