Manual

high enough that its effect on the performance of the mic is negligible. A good rule of thumb
is to have a preamplifier with input impedance at least five times the impedance of the
microphone. For example, if the mic is rated at 300 Ohms (as Royer’s are), the preamp
should have an input-impedance of at least 1500 Ohms. If the impedance of the preamp is
too low, the microphone will lose low end and body.
4. Transparency: A good preamp should sound natural with no edginess. Tube preamps sound
warm, yet wonderfully transparent. Transformer coupled preamps sound punchy. When
recording with condenser or dynamic microphones, engineers often choose mic preamps that
help warm up the mic, but warming up the signal does not need to be a consideration with
ribbon mics because they are by nature warm and realistic sounding.
Stereo Microphones and Ground Loops
Some preamplifiers are prone to developing ground loops when used in conjunction with stereo
or multi channeled microphones such as the SF-12. Ground loops can develop in the preamplifier
with any stereo microphone, regardless of the type (i.e. condenser, dynamic, ribbon). A ground
loop manifests itself as unwanted buzz or hum at 60 Hz and/or harmonics of 60 Hz.
The condition is brought on when the left and right transducer elements are plugged into two
inputs of a stereo or multi-channel preamplifier. The two three-pin male XLR connectors on the
SF-12’s splitter cable share Pin-1 as ground, so they are grounded to each other through the cable
set. If the grounding scheme within the preamplifier is poorly designed, or the distances to
internal ground are too great, a ground loop develops. The problem may be more apparent with
ribbon microphones because of the high gain required for proper operation.
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 lifter out of 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 would be preferable, but is often more difficult and/or expensive. In
conclusion, try to find the best preamp you can afford that has good gain characteristics and low
noise. Coloration is optional.
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 actually boost the upper
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