LM386 FAQ

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Some have mentioned why I made these LM386 audio boards rather than buy ones from Ebad [china].  I’m stumped how I can have one shipped to my house for less than it costs to mail the same thing across town and normally I can’t compete with the price.  I have to admit I own one of these little $2 boards and the do indeed work…..with some exceptions……

  • Good filtering is needed on the Vcc line.  LM386 IC’s are well noted for squealing, especially when higher gains are used.  Adding a .1uF bypass and 10uF or higher filter capacitor greatly reduces this problem.  Sometimes 220uF or 1000uF may be needed in some designs.  These capacitors are typically missing on cheap boards!
  • Cheap boards are fixed at the 200x gain level.  Chances are your project will be over driving the amplifier unless you are using this to amplify a direct conversion receiver.  To obtain the 20-200x gain levels the 0 ohm SMD resistor must be removed (for 20x gain) or replaced (for 20-200x gains).
  • The cheaper boards lack a DC blocking input capacitor.  Many times this is not needed but adding them is just a good practice.
  • My designs are based on values found in the TI LM386 datasheet.  I have seen cheaper boards vary from the specifications and use smaller/cheaper parts.  For example the recommended output capacitor is 200-250uF, many cheap boards use smaller values.
  • The Vcc and input circuits use standard .1″ pin headers with a terminal block for the speaker.  I found however using 5mm terminal blocks for all connections makes it easier to connect directly to shielded cable and wire without soldering or making female connector assemblies.  Of course terminal blocks cost a little more than a header pin.
  • Finally – My boards are designed to be built and enjoyed!

 

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