[MRCA] Mini Speaker Amplifier LM386 tips

[Tim]

I was at a concert once and the "stage" speakers each had a pair of 4-400's
in push-pull driving them.  HiHi

For low power battery operation the LM-386 is pretty ideal.  400 mW output
to a small speaker is quite adequate in a room or outside in a camp.  A 9V
battery usually lasts me all summer.  Except when I forget to turn it off
and leave it for a couple of days....
Tim
N6CC

On Tue, Mar 31, 2015 at 11:15 AM, Al Klase <ark at ar88.net> wrote:

> Ray and Zorro,
>
> The difference is the LM-386 was designed to run of a modest power supply,
> e.g. 9-volt battery, while the LM-383 is lusting after a Sears Diehard.
> Typical no signal currents are 4 ma. and 45 ma. respectively.
>
> There might be modern class-D (switching) devices that would let you have
> you cake and eat it too. Anybody have a handle on these?
>
> LM-386 kits, jack, volume control, PCB etc are dirt cheap out of China via
> E-bay.
>
> Al
>
> Al Klase – N3FRQ
> Jersey City, NJ
> http://www.skywaves.ar88.net/
>
>
> On 3/31/2015 1:31 PM, Ray Fantini wrote:
>
>> The LM-386 is a fairly piss week device with maybe a half watt output at
>> best. Instead of wasting time with that the LM-383 will provide five to six
>> watts of output into a 4 ohm load, requires a minimum of external
>> components and has output protection to take care of shorts or thermal
>> issues. The 383 was designed from the ground up as an audio power
>> amplifier, the 386 works for that but is perhaps more a general use op amp?
>> The only bad thing about the 383 for mill use is its maximum recommended
>> device voltage is 20 VDC but it will withstand up to 40 so it's not
>> designed to be connected directly to a 24 volt bus.
>>
>> Ray F
>>
>> -----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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