The isolation amplifier feature available on certain part numbers of the KX-155 Nav/Comm radio provides audio output from the KX-155 to drive a speaker. This feature was made available so that speaker audio was available for the KX-155 when used with Bendix/King's KA-134 audio selector panel which did not contain an internal speaker amplifier. Most audio panels include internal speaker amplifiers so this feature in the KX-155 may not be needed.