Preamplifiers - Avalon VT-737SP Operation Manual

Condenser microphones are typically more
sensitive than dynamic mics and are useful for
recording the harmonic details of instruments
and voices at lower volume levels such as
acoustic guitars, acoustic piano, and vocals.
Condensers also typically cover a wider
frequency range and pick up the complex
harmonics and overtones that come from
instruments such as acoustic piano, vocals,
horns, xylophone, vibes or cymbals.
Condenser microphones require a polarizing
voltage and power for their built-in amplifiers.
Sometimes provision is made to supply this
voltage directly through the microphone
cable. The procedure is called phantom pow-
ering, and the most common phantom supply
voltage available is 48V. Most phantom pow-
ered mics can operate on a wider range of
supply voltages from as little as 1.5V up to
50V. A commonly used condenser micro-
phone found in many professional recording
studios is the Neumann U87 and the AKG
C414.
Ribbon mics are constructed with a very light,
thin, corrugated metal ribbon that is stretched
within the air gap of a powerful magnet. The
ribbon is clamped at the ends but is free to
move throughout its length. When sound
strikes the ribbon, the ribbon vibrates in
response. As is the case with the dynamic coil
element, the moving ribbon cuts the magnetic
lines of force in the air gap, and the voltage is
thereby induced in the ribbon.
Page 36

6.5 Preamplifiers

A preamplifier is used to boost the signal of a
low level instrument or microphone to a
common usable level such as in a mixing con-
sole or recording device.
Most preamplifiers today are built around an
integrated circuit called an operational ampli-
fier or "op amp". Op amp preamplifiers are
widely used today in mixing consoles and
consumer preamplifiers because they are
inexpensive and widely available. However op
amp preamps distort easily, typically color the
sound, and do not retain the entire frequency
range of the signal. (Avalon does not use Op
amps for audio signal processing.
A high quality preamplifier like the Vt-737sp
retains the entire frequency and dynamic
ranges of the signal. High quality preamplifi-
ers operate in Class A and are made of
discrete electronics (no op amps), giving the
preamplifier less distortion and purer sound.
Avalon takes it a step further by combining
Class A mode and discrete electronics with
high voltage and high current design which
produce higher power rails and more head-
room for the biggest and purest sound possi-
ble. Avalon's 100% discrete, Class A pream-
plifiers require many specialized components,
a large power transformer, heat sinks for heat
dissipation and are therefore much more
expensive to build than preamplifiers built
around op amps.
Avalon Vt-737sp Operation Manual
Basics