Commentary

As the culmination of analog preamp, this control amplifier aims at the highest level with the performance and sound quality polished to the utmost by repeatedly examining and listening to each part. It is equipped with AAVA method volume control as well as the completion of all circuits.

Equipped with newly developed AAVA (Accuphase Analog Vari-gain Amplifier) volume control.
This volume control system is an entirely new concept that does not use a variable resistor. It has an analog structure that converts music signals from voltage to current, controls the gain by switching the current with a switch, and converts again from current to voltage.
The principle of operation is that the V-I converter converts the music signal into 16 types of weighted currents such as "1/2, 1/2 ² ,., 1/2 ¹⁵ , 1/2 ¹⁶ ". Each of these 16 types of currents is turned on/off by 16 current switches, and the volume is determined by the combination. The CPU (microcomputer) controls the switching so that the knob position and volume are the same. The combination of these currents changes the amplitude of the music signal. Variable It becomes a gain circuit (volume adjustment circuit), and the combined current at the final stage is returned to the voltage by the I-V converter.
The AAVA can vary the volume with 16 current switches that can be combined in 2 to the 16th power = 65,536 steps and have a resolution of 0.07 mV for a maximum output of 5 V.
Because the AAVA is an electronic circuit, the music signal does not pass through the variable resistor, so there is no thermal noise from the resistor. Moreover, because the music signal is not affected by impedance, the S / N ratio does not change even if the volume is changed. Moreover, there is no effect of distortion due to the an ultra-low distortion factor.
In actual volume control, a conventional variable resistor is used to detect the absolute value of the volume at the knob position, so that the same operation feeling as conventional volume is obtained.

The C-2800 amplifier circuit consists of a total of 18 unit amplifiers on the left and right sides, including input buffer, AAVA and balanced output. Each unit amplifier is arranged independently on the left and right sides on a glass epoxy motherboard.
These unit amplifiers are secured by an 8mm-thick rigid aluminum frame to prevent interference with each other, preventing electrical interference and mechanical vibration.

A logic relay control signal switching circuit is adopted to avoid routing of the signal path, and the shortest and straight signal path is constructed.

A newly developed R-toroidal transformer is used for the power supply, and the left and right sides are separated into monaural configuration together with a filter capacitor.
The R toroidal transformer uses a core with a circular cross-sectional shape to reduce magnetic loss and improve efficiency so that leakage flux is almost eliminated. In addition, the exterior uses glass fiber as a core material and has a three layer structure consisting of a two layer case made of a strong resin material and an epoxy filler with high vibration resistance and adhesion.

A printed circuit board made of Teflon (glass cloth fluorine resin) is used for the signal transmission circuit.
Teflon has the lowest dielectric constant and loss tangent, excellent high-frequency characteristics, and excellent heat-resistance. The C-2800 also features a gold plate on the copper foil to improve sound quality.

The gain of the preamplifier section can be selected in three stages.

With an emphasis on sound quality, it comes with a dedicated headphone amplifier.

Equipped with an EXT PRE function that can be switched with an external preamplifier.

It is equipped with compensator, phase switching function, attenuator function and subsonic filter to compensate for low and high sound volume.

It is stored in a Persimmon case.

There is a dedicated phono equalizer unit sold separately, and it can be used for analog record playback by adding it to the rear panel side.
The AD 2800 uses Teflon base material (glass cloth fluorine resin base material) and is stored in a sturdy aluminum case to reduce the influence from the outside.
In addition, the SN ratio is improved by connecting the input terminal and the amplifier circuit at the shortest distance, and a highly reliable DIN standard connector is used for connection to the main unit.

It is compatible with the phono equalizer units AD-290 and AD-290V used for the C-290 and C-290V, and can be used for the C-2800.
Also, AD-2800 can be used for C-290 and C-290V.

Model Rating

Analog disk characteristics show when AD-2800 is added
Type	Stereo Control Amp
Frequency Response	Balanced, Unbalanced : 3 Hz to 200 kHz + 0 -3.0 dB 20 Hz ~ 20 kHz + 0 -0.2 dB AD MM/36dB, MC input : 20 Hz ~ 20 kHz ± 0.2 dB AD MM/30dB input : 20 Hz ~ 20 kHz ± 0.3 dB
Total Harmonic Distortion Factor	0.005%
Input Sensitivity / Impedance (Rated Output / 0.5 v Output)	AD MM/30dB : 8.0mV/2.0mV/47k Ω AD MM/36dB : 4.0mV/1.0mV/47k Ω AD MC/62dB : 0.2mV/0.05mV/10 Ω, 30 Ω, 100 Ω switching AD MC/68dB : 0.1mV/0.025mV/10 Ω, 30 Ω, 100 Ω switching Balanced : 252mV/63mV/40k Ω Unbalanced : 252mV/63mV/20k Ω
Rated Output / Impedance	Balanced, Unbalanced output : 2V/50 Ω Rec (at AD input) : 252mV/200 Ω
S/N, input conversion noise	Input Short A - Correction EIA S/N S/N at rated output Input Conversion Noise AD MM/30dB: 95dB -137dBV 91dB AD MM/36dB: 89dB -137dBV 92dB AD MC/62dB: 80dB -154dBV 87.5dB AD MC/68dB: 75dB -155dBV 88.5dB Balanced: 111dB -123dBV 110dB Unbalanced 111dB -123dBV 110dB
Maximum Power Level	Balanced, Unbalanced output : 7.0 v Rec (at AD input) : 6.0 V
Line Maximum Input Voltage	Balanced, Unbalanced input : 6.0 v
AD Maximum Input Voltage (1 kHz, 0.005% distortion)	MM(30dB/36dB) input:300mV/150mV MC(62dB/68dB) input:7.5mV/3.75mV
Minimum Load Impedance	Balanced, Unbalanced output : 600 ohms Rec : 10k Ω
Gain (gain switch 18 dB position)	Balanced, Unbalanced input → Balanced, Unbalanced output : 18 dB Unbalanced input → Rec output : 0 dB AD MM (30/36dB) input → Balanced, Unbalanced output : 48/54dB AD MM (30/36dB) input → Rec output : 30/36dB AD MC (60/66dB) input → Balanced, Unbalanced output : 80/86dB AD MC (60/66dB) input → Rec output : 62/68dB * Gain switch can be switched between 12/18/24dB
Compensator (Volume -30dB)	1:+3dB(100Hz) 2 : + 8 dB at 100 Hz, + 6 dB at 20 kHz
Subsonic Filter	10 Hz, -18dB/oct
Attenuator	-20dB
Power Supply	100 VAC, 50Hz/60Hz
Power Consumption	48W
Maximum External Dimensions	477 mm wide x 156 mm high x 412 mm deep When adding AD-2800 : Depth 414 mm
Weight	21.2kg When adding AD-2800 : 22.1 kg
Attachments	Remote Commander RC-32 AC power cord Audio cable with plug (1 meter)
Sold Separately	Phono Equalizer Unit AD-2800 (¥ 200,000)