From: pcdhSpamMeSenseless@electrooptical.net   
      
   Christopher Howard  wrote:   
   > Hi, I had some LM386 chips on hand, and I downloaded the LM386 Low   
   > Voltage Audio Power Amplifier data sheet (Rev C).   
   >   
   > https://media.digikey.com/pdf/Data%20Sheets/Texas%20Instrument   
   %20PDFs/LM386.pdf   
   >   
   > I built, on a breadboard, the minimum part count application on page 8   
   > (Figure 10, section 9.2.1), except that I got rid of the 10k volume   
   > control resistor on pin 3, and I replaced the speaker with a 4 ohm   
   > resistor. Am using a 6V supply for pin 6, and feeding in test signals of   
   > about 5 kHz, amplitude 100 mV RMS.   
   >   
   > I'm finding, though, that — unless I ground out the input — that however   
   > I tweak the input frequency or amplitude, I still get garbage output.   
   > The output looks like some kind of complicated sum of many saturated   
   > signals of various frequencies.   
   >   
   > Does anybody have thoughts on where I might have gone wrong, to guide my   
   > troubleshooting?   
   >   
   > I re-checked my pin connections a few times, and the component values,   
   > which are reasonably close. I replaced the LM386 chip once as well, and   
   > got the same results.   
   >   
      
   It’s probably oscillating.  The 386 has a surprisingly large gain bandwidth   
   iirc. That and the crappy grounding and bypassing you get from those white   
   plastic slabs of misery cause a lot of problems of that sort.   
      
   Perfboard with no ground plane is almost as bad.   
      
   Dead bug construction is the ticket.   
      
      
   Cheers   
      
   Phil Hobbs   
   --   
   Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /   
   Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)