[MRCA] Mini Speaker Amplifier LM386 tips

[Mike Feher]

Z -

I have been seeing a lot of posts regarding the shortcomings od the 386
recently. I remember using them in all my home brew solid state rigs without
a problem. Maybe I was not smart enough to recognize a problem, but, to me
at the time, it was a "God-sent" device. 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 

-----Original Message-----
From: MRCA [mailto:mrca-bounces at mailman.qth.net] On Behalf Of B. Smith
Sent: Tuesday, March 31, 2015 11:48 AM
To: mrca at mailman.qth.net
Subject: [MRCA] Mini Speaker Amplifier LM386 tips

          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

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