Audio Database

The C-280 is a stereo preamplifier with two balanced line amplifiers and ten input terminals.

In order to realize balanced transmission with higher quality than conventional transformers, we have installed a balanced transmission line amplifier composed of two amplifiers, one for the hot side and the other for the cold side.
The same complimentary service differential push-pull amplifier circuit is used for each amplifier.
Also, the volume is controlled by a precision 4-channel volume (linked to LR channel) which is completely divided into hot and cold.

In addition to Class A push-pull in all amplifier stages, the cascode system is further advanced, and an FET is used in the load side of the cascode-connected amplifier, so that there is no need to worry about base current leakage when using a bipolar transistor. Thus, a reproduction sound with less coloring is required.

DC servo system by IC is adopted for all unit amplifiers, and DC drift is prevented by detecting DC generated at output and returning to input.
With the DC servo system and precise design, there is almost no DC drift, and all signal systems from MC input to output are directly connected.
The base plate is firmly fixed with screws, and the output element of class A amplifier and the element of constant voltage power supply are tightly fixed to the housing for heat dissipation, preventing resonance due to induction and vibration.

The power supply section has a dedicated power transformer for the left and right channels, making it a completely independent electrical and structural mono-construction.
In addition, in order to achieve low impedance over a wide range, each unit amplifier is equipped with a dedicated constant voltage power supply, resulting in a total of 6 multiple power supply systems.
The unit amplifier and the constant-voltage power supply section are housed in a thick aluminum housing and connected at the shortest distance to prevent an increase in the power supply impedance in the high frequency range.

In order to construct the shortest and straight signal path, relays are installed in every signal path where a switch is required, and these relays are controlled electronically by logic circuits for switching.
The relay used is a sealed type with nitrogen gas, which was developed especially for audio and communication equipment. The contact is a crossbar twin system of gold and silver-palladium alloy. It has high quality with low contact resistance and high durability.
In order to improve reliability, four circuits are used in parallel for the low-level signal path for completeness.

The basic circuit of the equalizer amplifier section is almost the same as that of one side of the line amplifier, but a low-noise element is carefully selected especially for the input stage of the differential amplifier.
The RIAA playback characteristics, which affect sound quality, consist of a network of resistors and capacitors. This section uses a Silbird Mica Capacitor, which has been developed specifically for audio.
This capacitor has a special processing and structure in which a silver thin film is formed by the screen method on a piece of purified high-purity mica, and a glass pattern (thin glass layer) is printed. This increases the corona discharge starting voltage and allows the signal to pass stably even at high voltage pulses. The lead wire, which affects sound quality, is connected directly to the edge of the silver film so that there is no degradation.

In the head amplifier section, a low-noise element is used for the input circuit, and at the same time, resistance noise is reduced by making the impedance of the NFB loop low.
In addition, in order to avoid the influence of the noise generated by the DC servo, not only the direct feedback method to the negative side of differential amplification but also the feedback to the base of constant current source is used. By this method, the influence of the noise of the servo system is almost eliminated, and SN close to the theoretical limit value is realized.

The MC input impedance can be switched between 3 levels of 10 Ω, 30 Ω, and 100 Ω in order to be able to handle various MC cartridges and control sound quality finely.
In addition to the normal head amplifier gain of 26 dB, a gain selector switch is provided to obtain a gain of 32 dB for the low-power MC cartridge.

Each input jack is specially made and used with a high-grade rhodium plated jack to prevent deterioration over a long period of time. It is 1 μ m thick and has high enough height to withstand 100 million sliding cycles. It also has excellent corrosion resistance, so it keeps good contact over a long period of time.

Equipped with an attenuator that instantly reduces the volume without changing the volume.
Uses a 3-step rotary system in which the level drops to - ∞ (silence) in the counterclockwise direction and -20dB and -30dB in the clockwise direction.

It is equipped with independent left and right attenuator type level control which makes the channel balance perfect and controls the orientation even if the listening point deviates.

It features a monitor switch that can record, play and monitor a tape recorder, a compensator that increases the volume in the low range, and a subsonic filter.

A thick Persimmon wood case is used for the gold-like scratch hairline panel.

Model Rating
Type Stereo Preamplifier
Frequency Response
CD, Tuner, Line, Tape Play : 1.0 Hz to 350 kHz + 0 -3.0 dB
20 Hz ~ 20 kHz + 0 -0.2 dB
CD, Line (Balanced Input) : 1.0 Hz to 700 kHz + 0 -3.0 dB
AD: 20 Hz - 20 kHz + 0 -0.2 dB
Input Sensitivity / Impedance
(Rated / EIA output 0.5 v)
AD (Head Amp off) : 4.0mV/0.5mV/47k Ω
AD (Head Amp + 26 dB) : 0.2mV/0.025mV/10 Ω, 30 Ω, 100 Ω
AD (Head Amp + 32 dB) : 0.1mv/0.0125mV/10 Ω, 30 Ω, 100 Ω
CD, Line, Tuner, Tape : 252mV/31.5mV/20k Ω
CD, Line (Balanced) : 252mv/31.5mV/40k Ω (20k Ω / 20k Ω)
Rated Output / Impedance Output (Balanced) : 2.0V/50 ω (25 ω / 25 ω), XLR-type connector
Outpput (Unbalanced) : 2.0V/1 ohm, RCA-phono jack
Tape Rec : 126mV/200 Ω (at AD), RCA phono jack
S/N / Input conversion noise
Input Short IFF-A Correction
Input Terminal Rated Input S/N Input Conversion Noise EIA S/N
AD(Head Amp off): 90dB -140dBV 86dB
AD(Head Amp +26dB): 78dB -152dBV 76dB
AD(Head Amp +32dB): 72dB -152dBV 76dB
CD, Line, Tuner, Tape : 115dB -128dBV 95dB
CD, Line (Balanced) : 115dB -128dBV 95dB
Maximum power level
(0.005% distortion rate, 20 Hz to 20 kHz)
Tape Rec : 19.0 V in AD
Maximum Input Voltage
(1 kHz, 0.005% distortion)
AD(Head Amp off):300mV
AD(Head Amp +26dB):15mV
AD(Head Amp +32dB):7.5mV
Minimum Load Impedance Output (Balanced) : 600 Ω (300 Ω / 300 Ω)
Output (Unbalanced) : 1k Ω
Tape Rec : 10k Ω
Gain CD, Line (Balanced) → Balanced Output : 18 dB
CD, Tuner, Line, Tape Play → Output : 18 dB
CD, Tuner, Line, Tape Play → Rec Output : 0 dB
AD (Head Amp Off) → Output : 54 dB
AD (Head Amp Off) → Rec Output : 36 dB
AD (Head Amp + 26 db) → Output : 80 db
AD (Head Amp + 26 db) → Rec Output : 62 db
AD (Head Amp + 32 db) → Output : 86 db
AD (Head Amp + 32 dB) → Rec Outpu : 68 dB
Loudness Compensator
(volume control -30dB)
2 : + 8 dB at 100 Hz, + 6 dB at 20 kHz
Subsonic Filter 10 Hz, -18dB/oct
Attenuator -20dB, -30dB, ∞
Semiconductors used Transistors : 219
FET : 58
IC : 26 pcs
Diodes : 174
Power Supply 100 VAC / 117 V / 220 V / 240 V, 50Hz/60Hz
Power Consumption 75W
External Dimensions 468 mm wide x 171 mm high x 396 mm deep
Weight 18.1kg