Introduction
There are two major types of RIAA phono equalization systems,
one is NFB (Negative Feedback) type and the other is CR type.
A representative preamplifier equipped with NFB type equalizer
is the MARANTZ Model: 7. This is a 3-step amplification NF equalizer
based on 12AX7, which applies NFB from the 3rd stage cathode
to the 1st stage cathode.(so-called "K-K type").
The
advantage of the NFB type is that it does not require a high
gain level and is not very sensitive to tube quality. However,
the impedance of NFB at high frequency range becomes very low
and results in a negative effect - the sound becomes hard and
dry. The NFB type is usually used as it is an easier way to attain
a good signal-to-noise ratio.
As for the CR type, a masterpiece
preamplifier equipped with the CR type equalizer is the vintage
Harman-Kardon Model: "Citation IV". CR type equalization
requires a high gain level and is much more sensitive to tube
quality.
Since tube quality will be directly amplified, the finest
possible quality tubes are needed for this type of equalizer.
Moreover, proper implementation is more difficult. However, the
CR type is much more superior sonically to the NFB type, being
very stable in the high frequency range and is able to reproduce
a very high quality sound especially when high quality tubes
are used.
 RS-28CX is equipped with the CR type equalizer based on GE(General
Electric/USA) 12AT7 authorized by J.A.N.(Joint Army & Navy)
standard of US Army, and can reproduce a very high quality and
clear sound without adding any NFB.
To avoid compromising on sound quality ,one of the solutions
we adapted to totally protect the sensitive CR type equalizer
from negative effects was to develop a separate power supply
unit. Likewise, some of the finest available high-end audio components
were selected for the RS28C to keep the deflection of the RIAA
curve below +/-0.3%.
Of course, the phono equalizer is only one
of the strengths of the RS28C. Another notable feature is a very
strong output voltage created by the Dual-Triode Tube 6CG7 of
General Electric(USA) used for the line stage. Leben further
selected the best quality tubes out of these and constructed
a powerful SRPP type amplification which can supply power amplifiers
with a maximum 80V of clean output signal.
In considering the
fact that output voltage of a standard preamplifier is more or
less 40V, the RS28C can output about two times as much voltage,
which will drive power amplifiers with very low input sensitivity.
Likewise, for using the RS28C with a high sensitivity power
amplifier, a 5-step attenuator is present in order to eliminate
residual noise from speakers. Leben also included two outputs
(one fixed and one variable) in order to cope with requirements
for adding a Sub-Woofer.
High Fidelity - Best Product 2008 |
