American R331 Ribbon Microphone

The model R331 microphone was made by the American Microphone Company of Pasadena.  It was introduced in 1950 at a list price of $75.00.  It is a compact microphone, only about 6 inches long and 2 inches in diameter.  On this basis, American called it a "full vision" microphone, an allusion to the face-blocking size of some of their competitors' products, such as the RCA 77 and the Altec 639.

The R331 was a ribbon design that gave a bi-directional (figure-8) response pattern.  For a slightly higher price, it could be had with an additional dynamic element (as the DR332), which gave it a unidirectional cardiod (heart-shaped) pattern.  For a lot more money ($250.00), the DR330 had a switch selectable pattern, and much wider frequency response.  All of these models had an identical appearance.  All external parts are anodized aluminum.  The lower section was advertised as black, but the dyes have faded somewhat, and have distinct purple tint in a bright light.

The nameplate could be removed to gain access to impedance selection links.  These microphones were provided with velvet-lined fitted storage cases.