[MRCA] Mini Speaker Amplifier LM386 tips

[B. Smith]

          When building your own "mini" audio amplifier  for your 
military radio using the LM386 chip it is important to not get greedy 
with the gain of the chip.  The chip has "default" amplification factor 
of 20 without any external caps or resistors. I suggest that you start 
off with that default  gain of 20  when using a military handset  set 
audio to drive the input. Combinations of caps and resistors between 
pins 1 and 8 can be added to allow selection of various  gain levels 
from 20 to 200! It is very easy to overdrive the chip with the high 
audio level from a military radio resulting in distortion.  Consult the 
data sheet for the chip for examples of different gain settings.
The Radio Shack amp uses a unique 1 transistor stage prior to the LM386 
and varies the gain on that transistor prior to the input of the LM386 - 
- - it is a great circuit and easily copied.  Then following that single 
transistor stage  on the Radio Shack amp using the  LM386 a combination 
of 10uF and a 100 ohm resistor is utilized between pins 1 and 8 to allow 
a fixed gain setting.
Z