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So what should we use with our beloved ribbon microphones? The features that translate
into top performance for a ribbon microphone are the following:
1. Lots of gain! A ribbon microphone works best with preamplifiers that have at least 60-
70 dB of maximum gain.
2. Low noise is a must! With this much gain being required for efficient operation of a
ribbon microphone, the noise characteristics of the preamp play a pivotal role in overall
performance of the captured acoustic event.
3. Load characteristics: A suitable preamplifier should have input characteristics that
impose the least amount of loading to the ribbon element. In other words, the input
impedance should be 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 pre’s
that help “warm up the mic”, but warming the signal up does not need to be a
consideration with ribbon mics because they are by nature warm and realistic sounding.
At this point personal taste should prevail over anything.
Stereo Microphones & 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 noise, buzz or hum
(usually 120HZ).
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 pair of three-pin male XLR
connectors of the stereo microphone cable usually shares 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 pre’s. The simple fix is to