Audio Database


Accuphase C-280V
800,000 yen(December, 1990 release)


The stereo preamplifier developed aiming at the extreme on the basis of the development technology acquired by C-280 and C-280L.

The balance transmission system is adopted as a line amplifier part.
This circuit consists of three differential amplifier fundamentally, and has the structure where amp1 takes charge of an input and amp2/amp3 take charge of an output. 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/amp3, respectively. 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.
The feature of this circuit is that both of amplifier operates even if it grounds one side of an output, and it can take out a double output. For this reason, it operates normally only by input and output connecting either to a grand (ground) line at the time of the imbalanced connection by the usual phono jack.
By this composition, the composition of amplifier changes neither as imbalanced as balance, but outstanding magnification is enabled.

Each unit amplifier of line amplifier consists of symmetrical type push pull circuits of Accuphase original.
Operation whose input circuit is a cascode sauce follower and which was stabilized to the super-high region is realized, and the output stage has realized the low Output load impedance and the outstanding linearity by the complimentary Darlington push pull.
All of these unit amplifier consist of direct connection amplifier, and it has prevented generating of direct-current drift by direct-current servo circuit in order to stop the shocking noise by a part generated in an output flowed in one direction.

The full independence power source of four transformers which separated not only right-and-left separation but the equalizer is adopted as a power-source part. For this reason, the full capacity of the filter capacitor amounts to 120,000 micro F.
Furthermore, the broadband constant-voltage power source was carried in all the unit amplifier, and the mutual intervention between amplifier is prevented thoroughly.

The adjustor developed specially because of C-280V is adopted as a volume control part.
CP (conductive plastic) element used as an object for studio is used for the resistance object, and CP resistance object is finishing the surface in the shape of a specular surface by carrying out high temperature pressurization plastic surgery after printing a resistive element, and has realized low contact resistance and a low distortion.
The brush in contact with a resistance object has adopted the gilding many contact type, is made into an external terminal and solid construction, abolishes a metal composition plane, and is reducing different-species metal distortion. Moreover, the rotary system has the structure where this is fixed and a resistance object rotates instead of the method which a brush rotates. Thereby, an internal contact surface decreases sharply, and contact grease also becomes unnecessary and it is improving durability.
Furthermore, a 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 has realized outstanding accuracy of survey of less than 0.5dB in a position of -60dB.

The logic relay control circuit is adopted as the change of a signal. The relay was installed in the required place, and with the circuit system which controls these electronically in a logic circuit, the change suppressed leading about of an unnecessary signal course, and has prevented signal degradation.
In this case, the full sealing structure relay containing [ which was developed the object for audios and for communication machines ] nitrogen gas is adopted especially as the relay used, and it requires. The contact which influences sound quality is a crossbar twin system of gold and a silver palladium alloy, and has become low contact resistance and a thing of high durability which has high quality.

All the circuit symmetrical type push pull circuits are adopted as equalizer amplifier.
It has the exclusive input circuit which matched the cartridge of each MM/MC, and constitutes from an FET element of high S/N at the time of MM input.
Moreover, since a minute signal is received by low impedance, the difference input circuit by a low noise element is constituted at the time of MC input, and it enables little reproduction of noise by attaining low impedance-ization of a NFB loop.
Furthermore, in order to take the characteristic of a cartridge, and matching, MC input impedance serves as a three-kind change type, and a profit can also be chosen from two kinds.

It is quantity 造 which was attached to the unit amplifier of a total of six right and left of line-in, line-out, and a phone equalizer, and stored the constant-voltage power-source part for exclusive use in thick aluminum housing at it, respectively.
It is being firmly fixed to housing to serve also as heat dissipation, and the element of an output and a constant-voltage power source has prevented resonance by vibration.
The whole structure is the framework structure by the hard aluminum of 8mm thickness, the mother board of thick glass epoxy is firmly attached to this, and aluminum housing is being fixed with the screw.

The characteristic jack of rhodium plating is used for an input-and-output jack. Rhodium plating has a track record as a connector of a communication machine or a computer, and has the outstanding durability.

Five step type rotary type Attenuator is carried so that a volume controller may be left as it is and volume can be adjusted in an instant.

It is possible to make channel balance perfect, to carry the right-and-left independent Attenuator type level control which can control the normal position by arbitrary listening positions, and to adjust for 0 - -6dB correctly at intervals of 1dB to -14dB a 0.5dB step and henceforth.
The resistive element has adopted the low distortion type of specular surface finishing.

The phase of the whole equipment was reversed and the phase switch which adjusts an absolute phase is formed.
In order that a change system may only replace + and - of balance amplifier and may not have a load circuit like a phase inversion machine, there is no sound quality degradation.

The Compensation switch which improves the shortage of massive at the time of small volume is carried.
With the position of the volume controller, the characteristic is rectified automatically and natural balance is maintained.

The Subsonic Filter is carried.

The front panel has adopted what gave the gold tone scratch hair line to the thick aluminum of Accuphase tradition, and has stored the main part in the persimmon wood case.


Rating of a mode
Form Stereo preamplifier
Frequency response
balanced input (CD, Line) : 1.0Hz-350kHz+0 -3.0 dB
20Hz-20kHz+0 -0.2 dB
CD, Tuner, Line, Tape Play : 1.0Hz-350kHz+0 -3.0 dB
20Hz-20kHz+0 -0.2 dB
AD: 20Hz-20kHz±0.2dB
THD 0.005% (with all the input terminals)
Input sensitivity/impedance
(at the time of an Output power / 0.5V output)
AD MM: 2.0mV/0.5mV/47kohm
AD MC (26dB): 0.1mV/0.025 mV/10ohm, 30ohm, 100ohm
AD MC (32dB): 0.05mV/0.0125 mV/10ohm, 30ohm, 100ohm
Balanced: 252mV/63mV/40kohm (20kohm/20kohm)
Unbalanced: 252mV/63mV/20kohm
An Output power/impedance Balanced output: 2.0V/10 ohm (5ohm/5ohm)
Unbalanced output: 2.0V/5 ohm
Tape rec: 252mV/200 ohms
S/N and input conversion noise
Input terminal Input short-circuit IHF-A compensation EIA S/N
Rated input S/N Input conversion noise
AD MM: 90dB -140dBV 86dB
AD MC(26dB): 80dB -154dBV 85dB
AD MC(32dB): 75dB -154dBV 85dB
Balanced: 111dB -123dBV 95dB
Unbalanced: 111dB -123dBV 95dB
Maximum-except-take-off level
(0.005% of a distortion, 20Hz - 20kHz)
Balanced output:7.0V
Unbalanced output:7.0V
Tape rec:19.0V
The AD maximum inlet pressure
(1kHz, 0.005% of distortion)
Minimum load impedance Balanced output: 600ohms (300ohm/300ohm)
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
AD MM input->Balanced output: 54dB
AD MM input->Unbalanced output: 54dB
AD MM input->rec output: 36dB
AD MC(26/32dB) input->Balanced output: 80 / 86dB
AD MC(26/32dB) input->Unbalanced output: 80 / 86dB
AD MC(26/32dB) input->rec output: 62 / 68dB
Loudness Compensation
(Volume -30dB)
2: +8dB (100Hz), +6dB (20kHz)
Subsonic Filter 10Hz, -18 dB/oct
Attenuator - 6dB-20dB-30dB, -infinity
The semiconductor used Transistor: 216 pieces
FET: 15 pieces
IC: 18 pieces
Diode: 158 pieces
Power supply voltage AC100V/117V/220V/240V, 50Hz/60Hz
Power consumption 53W
Dimensions Width 468x height 171x depth of 415mm
Weight 25.2kg