Shure Model 330 "Unitron" Ribbon Microphone
A supercardioid ribbon built for broadcast booths, priced at $120 when that was real money, and still the quietest way to reject a noisy room.
Overview
The Model 330 "Unitron" is a ribbon microphone. That explains almost everything about how it behaves in a room. Shure built it as a low-impedance, professional-grade transducer with a frequency response of 30 to 15,000 cycles, plus or minus 2½ db. That tolerance tells you the company cared about flatness and not just a pretty curve. The metallic ribbon is suspended between the poles of the magnetic structure. The magnetic circuit is efficient enough that the whole thing works at maximum efficiency in a small body. For a ribbon, that mix of bandwidth and compactness was the selling point.
The pickup pattern is supercardioid, with unidirectional characteristics that the company's own literature credits with effectively reducing background noise. In this case that is not marketing fluff. With the back of the microphone turned toward the audience, random noise drops by as much as 20 db. Owners who use one in a radio or TV studio, or in front of a live PA, notice it immediately. The mic hears what is in front of it and largely declines to hear the room behind it. That is the reason the 330 exists, and it is why the model turns up in broadcast work rather than in a casual home setup.
Impedance is selectable across three values - 50, 150 and 250 ohms - chosen by turning a screw on the face of the base. The screw sits on the shockproof base mount. Ribbon elements are fragile, so anything that isolates the body from stand-borne vibration is doing real work. Where unusually long cable runs are needed, use the lower impedance values. The permissible cable length is described as practically unlimited, since neither response nor level is appreciably affected by it. Shure sold extension cables (A26C) in 25-foot lengths with connectors, and they could be strung together for long runs.
The 330 will not drive an ordinary recorder directly. Its output level is very low, as with all ribbon microphones, so preamplification is required. For high-impedance inputs such as amplifiers and tape recorders, an A86A cable-type transformer is the right companion, and either the 50-ohm or the 250-ohm line can feed it. Skip that matching and the 330 will sound thin and distant for reasons that have nothing to do with the element. Period documentation puts the output at 87 db down open-circuit voltage level, which is a polite way of saying "bring a good preamp."
Durability is better than ribbon-mic folklore would suggest. The unit is described as impervious to temperature and humidity changes, and the only precaution necessary is to avoid mechanical shock.
The price was $120 list when the model was current. That placed it well above the company's own Commando series, where the Model 430 was $38.50 list, and squarely in professional territory. Tape-Recording (May 1958, p.25) covered the 330 alongside the 430 in a product report. The two were pitched at different buyers: one a broadcast-grade ribbon, the other a low-cost controlled-magnetic workhorse. Period testers who put the 330 through its paces found it lived up to the specifications claimed for it both as to quality and frequency response. A later retrospective in Electronic Musician remembered the 330 as a familiar broadcast and TV microphone with its supercardioid pattern and three-position impedance switch.
The supercardioid rejection is useful in an untreated room, and the three-impedance tap makes the 330 adaptable to whatever preamp is on hand. The ±2½ db response figure covers the low end and the top. It is not a mic to swing by the cable. It goes on a stand, gets aimed carefully, and is left alone, which is what broadcast engineers did with it.
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