Delay Line Distortion
By Wayne D. Zehner Jr. K9WZ
Description: Several years ago when ACC was still in business I had trouble with audio distortion when running the controller from battery backup power. They said the problem is the audio delay line chip SAD4096 did not having the correct bias on it to work at the lower voltage.
The Fix: The way that I corrected the problem was to put the repeater on battery backup (12.6 volts) and adjust pot 117, the audio delay line DC bias. They indicated to check the voltage on pin 8 and 9 of the SAD4096 and balance the voltage between the rails. This is done with out any audio through the chip when you are setting the voltage point. The notes that I have in my book indicate that I had 6.65 volts before I made any adjustments and 5.38 after. This seemed to work as I have not had any problems since then and the audio sounds good on power supply or battery back up.
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Article Copyright© 2003 Wayne D. Zehner Jr K9WZ
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