Many thanks to Dan Zellman, a former Syncron employee, who sent in this schematic for the AU7A condenser microphone. This was the ‘last issue’ diagram.
|Syncron AU7A factory schematic|
There are a few differences from my traced circuit that I posted in an earlier blog entry, most noticeably I had the 42V battery supply reversed. Also, I have worked on several of these mics, but have never seen one with the 470pF capacitor present.