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Topic: How to wire up LM386 amp for audio? (Read 10 times) previous topic - next topic

Runaway Pancake

#20
Oct 23, 2011, 04:33 pm Last Edit: Oct 23, 2011, 06:16 pm by runaway_pancake Reason: 1
I think that all you can really do is minimise distortion, you should avoid "overdriving" (clipping.)  You may have a portable radio and with fresh batteries at low and medium volumes it's OK, but when you really turn it up it starts sounding crummy - some of that's distortion, over-amplification, and some of it is just exposing certain limitations of the amplifier.

This sort of electronic sound, derived from a noise generator or noise generation techniques, isn't instrument-quality.  It sounds pretty nifty at low volumes, but there's a threshold whereat all of the faults can be appreciated. 

Anyway, the LM386 datasheet shows a X50 example.  It still uses the 10uF but with a 1200Ω resistor between it and pin1.  There is also a "bypass" capacitor that can be connected between pin7 and GND.  They don't give much guidance, text and example values from 0.1 - 10uF.
"When using the LM386 with higher gains (bypassing the 1.35 kΩ resistor between pins 1 and 8 ) it is necessary to bypass the unused input, preventing degradation of gain and possible instabilities. This is done with a 0.1 µF capacitor or a short to ground depending on the dc source resistance on the driven input."

Post Edit -- bonk inadvertent smiley
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justjed


in my diagram.. all pins 'are' labled.... can you not see them?  everything is labeled.. (except a missing 'to GND' lable)


He means functional labels, such as GND, SIGNAL, GAIN, etc.
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xl97

@justjed-

ahh..thanks.  I suppose that WOULD help people follow the diagram easier.  (I can make changes...np)

here is updated diagram...



showing a legend for PIN-OUT on the lm386 and the 10uF cap added for GAIN

@runaway_pancake-

some of it makes sense.. like over-driving.. makes the audio go 'crap' (clipping/distortion)

Im trying tp understand what it is I shoudl do from your comments..

1.) add a 1.2k resistor to the 10uF cap I added to the GAIN... yes?   (does it matter what side I put it on? +  or - side of the cap?)

2.) add a 0.1uF cap to pin 7 (bypass pin) to GND...


correct?


anyone care to help educate me about how to define or figure out anything about the signal BEFORE it goes to the amp/LM386?
was a comment about signal integrity BEFORE it goes there..  but I wouldnt have any clue on that.


a quick background on the sound INPUT (SND out from the PIC chip)..

I am using a PIC24FJ chip.. flashed with an API of some sorts to let noobs write generic code based on the API/instruction set.. (this 'code goes on .txt file on SD card..which is then loaded into the PIC chip upon powering it up)..

this is not mine.. I have no control over it..

however it has an EASY API to use..for doing simple things like PWM and playing audio..etc..  ( a very simple and generic platform)..

the PIC chip itself.. (somehow)  outputs Audio on its set pin(s)... this is what I am trying to use/tap so I can output to a speaker..etc..

anyways.. thanks you guys for the replies so far.. and understanding that not everyone has the skill sets you may have become accustomed to!  =)




CrossRoads

I was thinking more of posting a schematic.  This is much easier to see what is happening electrically.

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Runaway Pancake

1.) add a 1.2k resistor to the 10uF cap I added to the GAIN... yes?   (does it matter what side I put it on? +  or - side of the cap?)
I don't think it matters, but they show it between pin1 and Cap+, Cap- going to pin8.

2.) add a 0.1uF cap to pin 7 (bypass pin) to GND...
"Experiment for value", try various cap values, one lead to pin7 and the other to GND.  If it has a good effect then use it, if it makes things worse or has no effect then lose it.
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

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