Audio Database


Accuphase C-290
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.

The 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.
Furthermore, the 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 is prevented.
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.

Channel balance 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 carried.
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.

The 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.

4 The Unit
The The Low

Rating of a mode
In addition to this, refer to AD-290 of a category for AD input characteristics.
Form Stereo preamplifier
Frequency response
balanced input (CD, Line) : 3Hz-350kHz+0 -3.0 dB
20Hz-20kHz+0 -0.2 dB
CD, Tuner, Line, Tape Play : 3Hz-350kHz+0 -3.0 dB
20Hz-20kHz+0 -0.2 dB
THD 0.005% (with all the input terminals)
Input sensitivity/impedance
(at the time of an Output power / 0.5V output)
Balanced: 252mV/63mV/40kohm (20kohm/20kohm)
Unbalanced: 252mV/63mV/20kohm
An Output power/impedance Balanced output: 2.0V/50 ohm
Unbalanced output: 2.0V/50 ohm
Tape rec: 252mV/200 ohms
S/N and input conversion noise
Input terminal Input short-circuit IHF-A compensation EIA S/N
Output-power S/N Input conversion noise
Balanced: 111dB -123dBV 95dB
Unbalanced: 111dB -123dBV 95dB
Maximum-except-take-off level
(0.005% of a distortion, 20Hz - 20kHz)
Balanced output:8.0V
Unbalanced output:8.0V
Tape rec:9.5V
Minimum load impedance Balanced output: 600ohms
Unbalanced output: 600ohms
Tape rec: 10kohm
Gain Balanced input->Balanced output: 18dB
Balanced input->Unbalanced output: 18dB
Unbalanced input->Balanced output: 18dB
Unbalanced input->Unbalanced output: 18dB
Unbalanced input->rec output: 0dB
Loudness Compensation
(Volume -30dB)
2: +8dB (100Hz), +6dB (20kHz)
Subsonic Filter 10Hz, -18 dB/oct
Attenuator -20dB
Power supply voltage AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption 30W
The maximum Dimensions Width 475x height 149x depth of 405mm
At the time of AD-290 extension: Depth of 414mm
Weight 23.8kg
At the time of AD-290 extension: 24.8kg
Option Exclusive phone equalizer unit AD-290 (200,000yen)