December 29, 2012

putt putt putt

 Audio amplifier motor-boating sound.

Adding a Pre-Amp in front of the LM386 creating a Motor-boating sound when I increased the audio volume .

Obvious wasn't  due to interaction between audio amplifier circuit and radio frequency circuit .

A good shielding and power supply decoupling may solve this .

See 30 sec motorboating video clip .


1 comment:

wrhlamda said...

For my DC increasing the volume and at some point the sound disappear and at this point I can measure the 7 MHZ VFO frequency at the volume variable resistor . and later I found that increasing the volume to this point effect the biasing voltage of the pre-amp and that effect it's input impedance .but this problem disappear.but this problem disappear after some experiments on the mixer transformers and the filters after the mixer .and till now I don't exactly now what the problem is.