[Elecraft] KX1 speaker output with superimposed oscillation

[wb2srf at juno.com]

Hi Paco,

Sorry to read that it did not work for you.

LM386 amplifiers can do strange things when over driven. There is a lot
of available gain.

If the amplifier is operating properly, the Idle DC voltage with no audio
signal on the output pin 5 should be  half of the DC voltage measured on
the power supply pin 4 if not you may have a  leaky coupling capacitor on
the input circuit or a bad IC internal circuit throwing off the bias.

I have also found at times from building my own equipment that a de
coupling capacitor with short leads is needed across the power supply
pins 4 and 6  to keep it stable at high output levels especially if the
impedance of  the power supply is not low enough. I use a 10uF tantalum
capacitor  when connecting it is very important to observe the correct
polarity.

Also the RC network connected between the output pin 5 and ground is
required to keep the amplifier stable at high frequencies at different
loads.

GL 73,
Bob Johansen WB2SRF