|880,000 yen(November, 1993 release)
The preamplifier which aimed at the highest peak by improving all the circuits
further, examining all the materials and a part thoroughly based on the balance
transmission technology developed by C-280V, and keeping polishing.
balance transmission circuit is adopted as line amplifier. Balance transmission
is a system which sends simultaneously the positive/negative symmetrical signal
which the phase reversed mutually, and is excellent in the capability to remove
the noise ingredient in the common mode.
In C-290, it consists of three
differential amplifier, and at the time of balance, from +-both the inputs of
amp1, a signal enters, and is amplified, and it is inputted into the following
amp2 and amp3. 2 sets of these amplifier has a relation of tucking up its
sleeves with a cord which feeds back each output to the other party, and sends
out the symmetrical signal of +- by low impedance.
Even if the feature of
this circuit is the circuit system to which floating of the symmetrical signal
of +- was carried out from the ground and grounds one side of an output, both of
amplifier operates and an Output voltage does not change. Therefore, it is that
input and output only connect either to a grand (ground) line at the time of the
usual imbalanced connection.
All the unit amplifier is constituted from
original of an Accuphase, and a symmetrical type push pull circuit, and
operation whose input circuit is a cascode sauce follower and which was
stabilized to the super-high region is realized.
differential complimentary push pull circuit of the following stage is
modularized, and the alumina porcelain board also with the high frequency
characteristic that heat conduction is good for module material, and it is
sufficient is adopted. Thereby, with low noise, thermal and electric stability
is high and is improving reliability.
The output stage is maintaining the
linearity which was excellent in the complimentary Darlington push pull to a low
Output load impedance and the large amplitude.
The print board by woven
glass fabric base PRO (Polyphenylene Oxide) resin is adopted as a substrate.
This material is a tetrafluoroethylene (fluoride) resin base and the thing
which almost had the electrical property of this level, its dielectric constant
is low, the high frequency characteristic is excellent, and the engine
performance is compensated to 12GHz.
Furthermore, a golden plate is given to a Copper foil side, and also improvement
in sound quality is aimed at.
Right-and-left independence is achieved also with a power transformer
and a filter capacitor, and it has monophonic composition completely
electrically. Furthermore, the broadband constant-voltage power source was
carried in all the unit amplifier, and the mutual intervention between amplifier
Moreover, the amorphous core which was excellent in the frequency response
is adopted as a power transformer. With the alloy thin strap obtained by
super-quenching amorphous is a Molten metal, since [ without a crystal
structure ] metal amorphously, it has the character which was excellent
in the porcelain machine target compared with crystal structure metal.
As main features, since the maximum magnetic flux density is large, the
over-current characteristic is excellent. Since a curie point (temperature
to which a magnetic property changes suddenly) peculiar to a magnetic circuit
is expensive, there is almost no influence on the core by a temperature
change. Since there is little iron loss, such as hysteresis loss and an
over-current loss, there is that generation of heat is small etc.
It is Fe system core with an amorphous is a thickness of 25 micrometers
used for C-290.
4 linkage volume control machine which used
for the resistance object CP (conductive plastic) element adopted also as C-280V
is adopted as volume.
When CP resistance object carries out high temperature
pressurization plastic surgery after printing a resistive element, the surface
was finished in the shape of a specular surface, and has realized low contact
resistance and a low distortion. Moreover, the brush in contact with a
resistance object is a gilding many contact type, an external terminal and solid
construction are used, a metal composition plane is abolished, and distortion by
different-species metal contacting is reduced.
The rotary system has adopted
the structure where not the general system that a brush rotates but a resistance
object rotates, the internal point of contact is reduced sharply, and durability
of contact grease is improving by becoming unnecessary.
A very thick brass shaft 8mm in diameter is supported by an aluminum cutting
bearing, four elements are stored in a high precision aluminum cutting
case, respectively, a perfect shield is given, and improvement in sound
quality is aimed at.
A variable system is
continuation good transformation and the tracking error serves as survey of less
than 0.5dB in a position of -60dB.
The logic relay control circuit is
adopted as the change of an incoming signal.
The change installed the relay
in the required place and has prevented sound quality degradation by leading
about of a signal course, and contact degradation which poses a problem by the
change by a selector directly with the system which controls these
electronically in a logic circuit.
Moreover, the full sealing structure
relay containing [ which was developed as the object for audios and an object
for communication machines ] nitrogen gas is adopted especially as the relay
which have and is present in this circuit. The contact which affects sound
quality is a crossbar twin system of gold and a silver palladium alloy, and has
acquired low contact resistance and high durability.
It has the
composition that the exclusive constant-voltage power-source part was attached
to each of right-and-left a total of four unit amplifier, such as a line and a
balance amplifier circuit. In order to prevent these unit amplifier carrying out
a mutual intervention, it has stored in thick aluminum housing, and it fixed to
housing firmly to serve also as heat dissipation, and resonance by vibration has
also prevented the element of an output and a constant-voltage power source.
The whole structure is the framework structure by the hard aluminum of 8mm
thickness, the mother board of thick glass epoxy is firmly fixed to this, and
aluminum housing is being fixed with the screw on this.
is made perfect and the Attenuator of the 1dB step which can control the normal
position by arbitrary listening positions is carried.
Operation can be
changed to 0 to -6dB, and -infinity with a push button on either side,
respectively, and is displayed on the character display of a panel side.
The phase switch which reverses the phase of the whole equipment is
Since [ which replaces +- of the balance amplifier input unit ]
only, the change method does not have sound quality degradation in order not to
have an addition circuit like a phase inversion machine.
Compensation switch is carried in order to improve the shortage of massive at
the time of small volume.
With the position of a volume controller, the
characteristic is rectified automatically and natural balance is maintained.
The Subsonic Filter which cuts a super-low-pass noise is carried.
The power supply circuit was constituted and 6N quantity purity copper
wire is adopted as the power cord which gives a big effect to sound quality.
Moreover, the commercial power cord is also supported by making a power
source into a connector system.
Although C-280 has composition only for
a line, such as CD, the correspondence to a record is possible by an optional
exclusive phone equalizer unit.
The unit amplifier of a line and balance
can be carried in C-280V.
Change of sound quality can be enjoyed by
exchanging the line balance amplifier unit (four pieces) of C-280V.
In addition to this, refer to AD-290 of a
category for AD input characteristics.
|balanced input (CD, Line) :
||3Hz-350kHz+0 -3.0 dB
|CD, Tuner, Line, Tape Play :
||3Hz-350kHz+0 -3.0 dB
||0.005% (with all the input terminals)
(at the time
of an Output power / 0.5V output)
|An Output power/impedance
||Balanced output: 2.0V/50 ohm
output: 2.0V/50 ohm
Tape rec: 252mV/200 ohms
|S/N and input conversion noise
short-circuit IHF-A compensation
||Input conversion noise
a distortion, 20Hz - 20kHz)
|Minimum load impedance
||Balanced output: 600ohms
Tape rec: 10kohm
||Balanced input->Balanced output: 18dB
Balanced input->Unbalanced output: 18dB
Unbalanced input->Unbalanced output: 18dB
input->rec output: 0dB
2: +8dB (100Hz), +6dB
||10Hz, -18 dB/oct
|Power supply voltage
|The maximum Dimensions
||Width 475x height 149x depth of 405mm
the time of AD-290 extension: Depth of 414mm
At the time of AD-290 extension:
||Exclusive phone equalizer unit AD-290 (200,000yen)