Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!amdahl!pacbell!att!ttrdc!ttrde!pfales
From: pfales@ttrde.UUCP (Peter Fales)
Newsgroups: sci.electronics
Subject: Re: Help needed with audio amp IC
Message-ID: <853@ttrde.UUCP>
Date: 13 Feb 89 21:06:37 GMT
References: <7901@netnews.upenn.edu>
Distribution: usa
Organization: AT&T, Skokie, IL
Lines: 30

In article <7901@netnews.upenn.edu>, depolo@eniac.seas.upenn.edu (Jeff DePolo) writes:
> 
> Has anyone played with the Radio Shack audio amplifier IC?  I don't
> remember the model # or catalog #, but it's a 8-pin IC.  I have a few
> of them that I got god knows where (some surplus stuff), and they come
> with the pin-outs, but no specifications.  There are 2 pins labled
> Gain.  I supposed I have to connect them via a resistor or something to
> adjust the amplifier gain, but I don't know what I need.  I've had
> the amplifier working, but they seem to overdrive themselves and eventually
> burn out.  Does anybody have any information on them?


This is probably the LM386 (National Semiconductor).  I know RS sells
the LM386 and it comes in an 8 pin package.  According to my data book
the simplest configuration has a gain of 20 with nothing connected
to pins 1 and 8.  With a 10 microfarad capacitor between the two pins
(+ on pin 1) the amplifier has a gain of 200.  Intermediate values
can be selected by also putting a resistor (value not given) in series
with the capacitor.  The chip has internal 1.35K resistor between the
pins.

How are you driving the speaker?  The chip can drive an 8 ohm speaker 
directly, but should have a 250 microfarad cap in series with the 
speaker to filter out any DC.

-- 
Peter Fales			AT&T, Room 2F-217
				200 Park Plaza
UUCP:	...att!ttrde!pfales	Naperville, IL 60566
Domain: pfales@ttrde.att.com	work:	(312) 416-5357