[Laser] WB9AJZ laser RX problems

[laser@mailman.qth.net]

Hi Wendell


The LM386 can self oscillate:

1) If there is insufficient capacitance at the supply pin to ground.

2) If you leave out the series resistor and capacitor from the audio output 
pin to ground. (zobel network)

In my RX I use a LM386 with 2.2 Ohms in series with 100nF to ground and a 
1000uF out to the speaker. The 2R2 / 100n should be right at the pin, not 
across the speaker.

I've also used a 1k in series with a 1uF non polarised capacitor to reduce 
the open loop gain. This goes between the two gain contol pins.
(OK I can't tell which ones they are as I've built it deadbug style and it's 
upside down. But its either pins 1 and 8        or possibly 4 and 5.)


 Good luck


73

David  G0MRF         www.g0mrf.freeserve.co.uk/laser.htm 


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