help me with evil LM386

[smoguzbenjamin]

Hey all.

I just breaboarded an LM 386 amp and it is distortion like crazy. I used a 1M pulldown R, 10uF cap into LM396 -input, and a 100uF cap between LM386 output and the speaker+. Good distortion but I'm wondering what's wrong. See at first the clipping sounds good but as the note decays it starts gating. :mrgreen: It's a 4ohm speaker , is that the problem?

[smoguzbenjamin]

Come on :mrgreen:

[slajeune]

Hi smoguzbenjamin,

my turn to help you!!!  Pin 1 and 8 control the gain of the LM386.  Put a resistance between pins 1 and 8.  More resistance = less gain (if I remember correctly).  Try various resistors there and let us know!

Thanks,
Stephane.

[spongebob]

Have a look at http://www.national.com/ds/LM/LM386.pdf, it has some schematics on how to wire this thing up...

[smoguzbenjamin]

I put a 5k pot inbetween pins 1 and 8. More resistance = not enough gain to drive the speaker. It's rated from 100Hz to 30kiloHz @ 4ohms and the rest of the sticker was peeled off. :?

thanks bob I'll take a look at that

[Ge_Whiz]

What supply voltage are you giving it? Battery or wall-wart?

[RDV]

Ground the inverting input which should stabilize it. 10uf is too big for a in-cap, try .01 or smaller, and 220uf for the out-cap allows more bass.

Regards

RDV

[Joep]

As you see in the datasheet, if you leave pin 1 and 8 open you will have the lowest gain. If I remember well at this setting you already have quit some distortion with a medium power humbucker guitar.

Is it really a gated sound you hear? Mine was oscillating with also gives a "gated-ish" sound. Try a small(!) cap (100n or something, not critical) between ping 4 and 6. This stoped oscillation in my circuit and is sounded a lot better.

Later,

Joep

[Ansil]

a .047 is a nice input cap,  for an amp i would go with a 470uf outcap if you have a wall wart  a 220uf i cyou are using a batterie.

grounding the unused input is ok,  but if you are using the non inverting try using the inverting as they tend to be more on the stable side.  also a 100uf to ground from the seventh pin is nice.

also if you are using the N-1  then smack yourself and get an n-3  cause ratshack is screwing people packing a n1 in a n3 package

[smoguzbenjamin]

I knowingly got an N1 because the local dudes didn't have nothin else :evil:

I'm using the inverting input, got the non-inverting input to ground. My guitar's a single-coil so hot pickup's ain't the problem. I have pin7(bypass) unconnected. Should I ground it? When I left the guitar unplugged I got a whiny oscillating tone so that's probably the problem.

Joep, pin 6 is power in, pin 4 is ground so what difference will the cap make? :? This chippy is more unstable than I suspected... :?

[RDV]

I'm not saying that you should copy the 'Little Gem', but there's probably something in there that will help, like the little filter circuit on the output.
http://runoffgroove.com/littlegem.html

Regards

RDV

[smoguzbenjamin]

Actually the little gem made me buy a few 386's And I think I breadboarded it and it was also fuzzzzzy.

[Gus]

The brand of IC used makes a difference here.  IIRC you want to use a JRC386

[smoguzbenjamin]

It says:

Code Select Expand


(logo) JM02AG
      LM
      386N-1


I can't get anything else

[Joep]

Hi Smoguz,

The small capacitors are used to get rid of the high frequence stuff. The capacitance of electrolity capacitor lowers rapidly  on high frequencies. So it is always good to add and extra small cap.

Later,

Joep

[smoguzbenjamin]

Oh yeah that makes sense. I'll try that I've got a 0.05uF cap lying around from the little gem experiment. Gotta find time though, combining school with electronics and girlfriend is tough

Hey we've been going out for 16 months today

[Ansil]

The brand of IC used makes a difference here.  IIRC you want to use a JRC386

(vomits  projectiles)  sorry never had good luck with the jrc one.  someone sent me a whole slew of them to play with  once , and not only could i not get the right voltage ones.  but they just werent' reliable.

[smoguzbenjamin]

Hang on that's a damn good idea. I might just not have enough headroom! N1, that's supposed to be 5-12V right? Maybe I should try feeding it 12V see if that helps...

[idsnowdog]

I was doing some research into building an ugglyface and I ran across a replacement for the lm386 chip.  It is called the nte823.  It has the same pinouts and frequency range but where the lm386 has noise rejection at 50db the nte823 has 250db.  You can find the pdf data sheets and compare them.  The cell phone industry uses them to keep noise to a minimum.

Snowdog

[Ansil]

I was doing some research into building an ugglyface and I ran across a replacement for the lm386 chip.  It is called the nte823.  It has the same pinouts and frequency range but where the lm386 has noise rejection at 50db the nte823 has 250db.  You can find the pdf data sheets and compare them.  The cell phone industry uses them to keep noise to a minimum.

Snowdog

nice  .. thanks i may have found a new favorite chip.. ps try the lm380