What is it about RCA products? Why should we care about old ribbon mics from the 40’s when today’s products like Royer and AEA - Cole ribbon microphones bring so much great quality to a session. To this day when you talk about recording a horn section, acoustic guitar and even a guitar amp peer engineer(s) often says with a smile “have you tried using a ribbon mic, like a…..” Since most of us know the value of the ribbon sound on a track. I have often replied that’s a great idea, I should use my RCA mics and the comment that is often uttered back is ”You have RCA mics, I would love to hear those”. It’s true there great! it really makes you feel good about the session. It’s like taking a Sunday drive in an restored classic car while using today’s technology, it’s the best of both worlds. When we record with these mics I often think about historic recording sessions at Capital, Sun, Stax & Motown studios when the RCA was one of the only choices, and they used them to create the music we still listen to today. I would like to thank the creator of this educational RCA microphone site. It is a great resource and I would like to share his work with you about the RCA microphones that we use at Fastback.
74-B Microphone: The 74-B has been widely used by broadcasters for years. It offers the smooth bi-directional response of the 44-BX in an inexpensive, small and light-weight model. The 74-B is particularly recommended for applications where the extended frequency response and more elaborate shielding and shock mounting of the 44-BX are unnecessary. It is, therefore, a very useful microphone for audition studios, announce positions, talk back and for small and occasionally used studios. It may also be used for remote pickups where the frequency response is limited by lines and other factors. In design the Type 74-B is similar to the larger 44-BX, but lacks the latter’s shock mounting and transformer shielding. The transformer output impedance taps are for 50, 250, and 15,000 ohms. The windscreen is finished in satin chromium and the base is umber gray. Attached to the base is a ball and socket joint which permits rotation or tilting at any angle.
77-DX Microphone: The RCA Type 77-DX Poly-directional Microphones MI-4045-F and MI-11006-C are high-fidelity microphones of the ribbon type which may easily be adjusted to obtain a variety of directional patterns. Since the MI-4045-F microphone is primarily intended for broadcast use, it is finished in satin chrome and a low-gloss umber-gray enamel. The MI-11006-C microphone is intended for television use and is therefore completely finished in a low-gloss umber-gray enamel which eliminates glaring reflections usually seen on highly polished microphones.
Instead of being open on both sides as in the conventional velocity microphone, the ribbon element in this microphone is coupled to an acoustic labyrinth which forms the body portion of the microphone. The tube connecting the back of the ribbon to the labyrinth is slotted directly behind the ribbon and fitted with an adjustable shutter to secure various areas of opening. When the opening is completely closed, the microphone operates as a non-directional pressure microphone; at the wide-open position the microphone becomes bi-directional. With the proper size opening the pattern becomes a cardioid by virtue of the phase shift which occurs. Openings smaller or larger than this critical size produce directional patterns with various sized rear lobes. Different amounts of low-frequency attenuation are obtained by a reactor shunting the output. These microphones are intended primarily for indoor use and if used outdoors may require some additional protection against the wind.
Directional Characteristics: The adjustable shutter over the slot in the tube leading to the acoustic labyrinth may be rotated by means of a screwdriver adjustment extending through the rear screen flush with a designation plate. The choice of directional patterns makes possible a considerable degree of control of the ratio of direct sound to reverberant sound as well as the possible reduction of unwanted sound such as audience noise in a studio. The wide angle of pick-up provided by the cardioid pattern is useful in covering large groups with a single microphone. For close-talking applications the non-directional characteristic is of considerable value since the low-frequency response is not accentuated as in the case of a velocity microphone. Numerous other applications of the various directional patterns as well as the different response curves will no doubt suggest themselves to the user.
Directional Pattern Selector: The plate is marked U, N and B, as symbols for the uni-directional, non-directional and bi-directional patterns. Three additional markings L-1, L-2 and L-3 are used as reference points for other directional patterns which may be obtained. Refer to Figure 4 for the patterns associated with each of the six symbols. Stops are provided on the continuously variable pattern selector at the six marked positions, although the shutter may be set at any intermediate position.
Frequency Response Settings: At the bottom of the lower shell is a screwdriver-operated selector marked M (music), V1 and V2 (voice). The voice positions connect a reactor across the entire secondary or part of the secondary of the output transformer, depending on the switch position. Refer to Figure 5 for the frequency-response characteristics of each setting. As can be seen from the curves, the reactor attenuates the low-frequency response. This is especially desirable when the microphone is less than three feet from the source of sound and the low-frequency response would otherwise be exaggerated.
BA6A Compressor: The BA6A is very transparent no matter what its function. For example, the RCA BA6A limiter/compressor has a very characteristic tone that many recordings have been constructed with. The BA6A was built without cutting corners or scrimping on components and first built for radio stations thought out the US. As new lighter and smaller compressors where introduced on the market radio stations slowly phased the BA6A out and during that time more of these BA6A’s where thrown in the garbage than put back into the market place. The BA6A is only a single channel, but well worth the time it takes to set it up for the session.