Unlike the previous two models, which run on standard 48V phantom power, the AM40
is a hybrid FET/tube model and so requires a dedicated PSU. The PSU itself is built
into a compact steel case with a switched IEC mains socket, a red status LED and
XLR connectors for the mic and for the output. No other controls are fitted to the
PSU and there's no mains voltage selector. As with the AM30, the whole kit comes
in a camera case and the AM40 also includes the necessary multicore lead to connect
the mic to the PSU.
The same pad and roll-off switches are fitted and the paper spec looks virtually
identical with similarly low noise and distortion figures. Opening the body reveals
the tiny GT5840M Nuvistor tube, hard-wired to the circuit board. These little tubes
require only 6 Volts to operate, which is claimed to produce cooler operation and
hence less noise than more conventional valves. A Cinemag nickel-core output transformer
completes the signal path.