lamination has a high relative permeability, which is one of the
factors contributing to low distortion and higher dynamic range.
The ECC 88 tube used in the Cactus is a single subminiature
pentode in a triode mode. After being burned in for a week, this
tube is hand-selected by Blue personnel for optimum low-noise
performance. The amplifier input is separated from the micro-
phone capsule with a polystyrene capacitor. Both the tube grid
and the microphone capsule are controlled through high-quality,
low-noise 0.5W 400Mohm resistors. High-end film capacitors
and low-noise metal oxide resistors are used throughout the
Cactus circuit.
All of the Cactus microphone’s internal wiring is oxygen-free cop-
per Teflon-insulated.
Power Stream Power Supply
The Blue power supply for the Cactus microphone is based upon
our Power Stream model, and features a sophisticated, regulated
circuit design as well as other features that are not available
in any other commercially available tube mic power supply. To
assure the longevity of the vacuum tube and the stability of the
tube microphone circuitry, Blue has developed the Power Stream
power supply with the new SOFT START feature.
In the past, power supplies have been designed to use both heater
and plate voltages applied simultaneously once power has been
switched on. In this case, the high voltage potential on the plate
forcefully attracts electrons from the not yet heated cathode,
a process is known as “cathode stripping”. In practicality, this
means that each time the power supply is switched on, the micro-
phone tube changes its electrical properties. To put it simply, the
tube begins to wear and gets noisier.
To avoid this problem the Power Stream’s SOFT START feature
delivers the tube’s heater voltage first. The Power Stream’s
circuitry also prevents the heater current from exceeding the
limits for which the tube was designed. Without this feature the
cold heater would draw more current than specified, and begin to
Percussion
On tambourine, shaker, bells, clave, and orchestral percussion
the Cactus offers astounding clarity and realism, and can be
positioned quite close to a percussive source without distortion or
undue proximity effect. Start by placing the Cactus about a foot
from percussive instruments. Selecting a cardioid pickup pattern,
or moving the mic closer to the source will emphasize detail and
tone, as well as decreasing the proportion of ambient room sound
on a track. More distant placement, or the use of an omnidirec-
tional or figure of eight pattern will yield a natural, roomy sound
that blends easily with other rhythm instruments.
The Technical Page
The Cactus vacuum tube amplifier consists of a classic common
cathode circuit. The amplified signal is taken from the plate and
fed through a high-quality polypropylene capacitor, then output
to our Blue custom hand-built transformer. The capacitor has a
low dielectric absorption coefficient and a low equivalent series
resistance. These parameters are essential to high end audio, and
are not present in lower priced microphones.
D.A. (dielectric absorption) is reluctance on the part of the capaci-
tor to give up stored electrons when the capacitor is discharged.
E.S.R. (equivalent series resistance) is the resistance composed
of the capacitor plate, lead, and termination resistances. If the
capacitors used in the audio path possess high values of D.A. and
E.S.R., the result is a loss of accuracy and dynamic structure
when reproducing the finer details of the recorded source. Under
these conditions, a definite “grunge” or hashy distortion is added
to the reproduced signal.
A special output transformer was designed by Blue engineers to
match the tube, and to ensure complete immunity from outside
interference (RF and other sources). This hand-built transformer
is balanced, using a symmetrical two-bobbin design (i.e.
humbucking), with a transforming ratio of 10:1. With this ratio, the
microphone achieves a low output impedance, typically 150 ohms.
The primary transformer windings are connected in parallel,
and connect directly to the XLR output pins. The transformer
Summary of Contents for Cactus
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