This card has been designed to replace the hard to find AA-206 audio card that fits in the ACL, AITKEN or NORLIN
SR-209 and SR-219 surveillance receivers.
This replacement provides one or two 8 ohms unbalanced audio channels instead of the 600 ohm balanced audio channel delivered by the original card.
It uses the well know LM386 audio amplifier and works as well as the original one.
Main audio channel output is wired as the original AA-206 600 ohm ouput (AA-206 pins 10 and 12) but with one leg tied to ground allowing
a 8 ohm loudspeaker to be connected to the rear connector (TB1.5 and TB1.6). Auxilliary audio channel is wired to the original AA-206 150
ohm output (AA-206 pin 11) which is not wired to any external connector. It could be used to drive an internal loudspeaker.
Power supply comes either from the main 24V or from the Squelch driven 24V. It is converted to the required 12V by a voltage regulator.
The original SR-209 power supply should be able to deliver the required additional amount of current.