royer SF-12, Инструкция по эксплуатации и Руководство пользователя

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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.
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