You can perform a simple test to check for this condition (preferably done with a pair of
headphones to avoid feedback). Plug one side of the stereo microphone into either preamplifier
input. Listen to the output of the preamp. All should be quiet except for the mic signal. Now plug
the second side into the next preamplifier input. If a noise or buzz develops, you have a ground
loop. The ground loop may be very slight or more pronounced, depending on the preamp.
Battery powered preamps usually do not exhibit this problem, and neither do well designed, line-
operated mic preamps. The simple fix is to disconnect one of the microphone’s two Pin-1 ground
connections. A better method is to make a small ground-lift adapter fashioned from a male-
female XLR barrel adapter. Switchcraft makes a very nice one and it takes less than five minutes
to wire it up. Simply connect Pin-2 to Pin-2, Pin-3 to Pin-3, and leave Pin-1 disconnected.
Correcting the problem at the preamplifier is preferable, but is often more difficult and/or
expensive.
Equalization and Ribbon Microphones
One of the great strengths of ribbon microphones is how well they take EQ. Even with
substantial amounts of equalization, ribbons retain their natural, “real” quality. For example,
when a lead vocal is being performed on a ribbon microphone, you can boost the upper-end
frequencies to the point where the ribbon mic emulates the performance curve of a condenser
mic with excellent results. This is not to say that a ribbon microphone can replace a quality
condenser mic, but the EQ friendliness inherent in ribbon microphones does allow for an
enormous amount of flexibility.
The reason that ribbon mics take EQ so well is their inherent low self-noise, unusually smooth
frequency response characteristics and freedom from off-axis coloration. Dialing in high
amounts of equalization on condenser or dynamic microphones also means dialing in extra
amounts of the microphone's distortion products and self noise: garbage that contributes to an
unnatural, unpleasant sound. Because distortion and self-noise are almost nonexistent in ribbon
microphones, high levels of EQ can be used without incurring harshness or excessive noise.
Hum, Noise and Mic Orientation
All dynamic microphones, including ribbons, are susceptible to picking up stray alternating
magnetic fields. Power transformers (such as those found in guitar amplifiers) and alternating
current motors are the most likely sources of hum. In-wall wiring and electrical utility
transformers are other likely sources. A well-designed microphone provides shielding to
minimize the effects of such stray magnetic radiation. In some cases complete isolation is
impossible and the result is usually hum or buzz. Unpowered microphones are more susceptible
to hum pickup after the mic, for example through the cable set. With vintage ribbon
microphones, which often employ large, bulky magnet structures and are often poorly shielded,
the problem can be worse.
The SF-24V reduces this condition because the essential gain is provided at the microphone,
negating the need for additional gain to be supplied by the preamplifier. All Royer SF-series
microphones (SF-1, SF-12, SF-24, SF-24 Live and SF-24V) are designed to minimize the effects
of unwanted radiation by integrating the transducer barrel as part of the magnetic return circuit.
They also incorporate toroidal impedance matching transformers, which have a natural ability to
repel magnetic radiation.
12
Summary of Contents for SF-24V
Page 21: ...Polar Pattern Frequency Response 21 ...
Page 22: ...Wiring Diagram 22 ...
