Five Classic RCA Ribbon Microphones

by Mike Dorrough, KO6NM, and Gary Halverson, WA9MZU

44A, 44B/BX

Successor to the 77A, the 44 could be considered a "cost-reduced" version. However, it was this cost reduction that catapulted the 44 to its legendary commercial success. Even today, some fifty years after its introduction, 44's can be found in broadcast and recording studios throughout the world.

The first of the 44 family was the 44A, a large microphone, although considerably smaller than the 77A. It used a large horseshoe magnet around the ribbon and featured a figure-8 pickup pattern.

The slightly larger 44B was introduced in about 1938. It also had a figure-8 pickup pattern. Both the 44B and the BX were bi-directional having figure-8 patterns.Its frequency response extended from 30 cycles to 15,000 cycles.

Within it's case, the 44 was provided with "V" (voice) or "M" (music) jumper positions. When a lead was connected to the terminal marked "V", a choke was connected in parallel with part of the transformer winding, which substantially attenuated the low frequency response.

The basic difference between the suffixes within the 44 family were:

• The 44A generally had a bronze finish
• In contrast with the 44B and 44BX models, the later 44BX had the ribbon mounted farther toward the rear, giving it a smaller figure-8 on the back side.
• The 44B was finished in a distinctive black with chrome ribbing on the lower portion, while the 44BX was an umber grey and stainless steel (Japan Black was optional). Both had the red "meatball" logo in the front center of the lower portion between two bands of ribbing that wrapped around the microphone.

The 44 BX was manufactured up to around 1955.

7B C, D, DX

The 44 was replaced in the late 40's by a smaller, restyled version: the 77B. Resembling a large capsule, the 77B and its decendents, the 77C, 77D and DX have become the standard microphone icon known throughout the world.

Like its ancestor the 77A, the 77D and DX had an acoustic labyrinth in the body of the microphone. However, they were polydirectional microphones. Their polydirectional capability was accomplished by a tube connecting the back of the ribbon to the labyrinth that was slotted directly behind the ribbon and fitted with an adjustable shutter to close off portions of the opening. By positioning the shutter to completely close off the opening, a non-directional could be obtained. When the opening was wide open, the pickup pattern was bi-directional. Positions in between produced other pickup patterns.

Unlike the 44, the instructions claimed the 77D could be "close talked" when in the non-directional configuration as the low frequency response was not accentuated.

The low frequency attenuation could also be attenuated by switching in a choke across the output of the microphone. A screwdriver-operated switch was provided at the bottom of the lower shell. Positions were marked M (music), V1, and V2 (voice).

Although the 77DX enjoyed a long commerically successful product life with a number of different letter suffix models preceding it, two basic versions of each type were offered: a satin chrome version (the broadcast model), and a non-reflective umber grey version (the TV model). Given a choice, collectors perfer the broadcast model due to its distinctive contrasts.

The basic differences between the 77D and 77DX models are that the 77DX had an improved magnet and transformer, which produced a little more output. The 77 was discontinued around 1967 and replaced by the BK-11.

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