Audio Database
C-250
Commentary

Based on Acuphase's unique balance transmission technology, this stereo preamplifier aims at a new age by simplifying the design and circuit aspects, and by using carefully selected elements and thoroughly polished performance and sound quality.

The line amplifier uses a unique balanced transmission method.
Balanced transmission is a method of simultaneously transmitting positive and negative symmetric signals whose phases are inverted with each other. It is excellent in the ability to remove the noise component of advisory mode.
The C-250 basically consists of three differential amplifiers. When balanced, the signals from the + - inputs of Amp 1 are amplified and then fed to Amp 2 and Amp 3. These two amplifiers are connected to each other by feeding their outputs back to the other side. They transmit + - symmetric signals with low impedance.
This circuit is an ideal circuit system in which the + - symmetric signal is floated from the ground. Even if one side of the output is grounded, both amplifiers are differential and the output voltage does not change. Therefore, in a normal unbalanced connection, either input or output is simply connected to the ground line.

The main circuit of the C-250 consists of a total of 6 unit left and right amplifiers including a line amplifier, a balanced input / output amplifier and a balanced output amplifier, and is located on the motherboard.
In order to prevent mutual interference between these unit amplifiers, each unit amplifier is surrounded by a thick extruded aluminum material, and the structure is strong against resonance due to external vibration.

The power supply section has a completely monaural configuration with independent power transformers, left and right filters and capacitors to eliminate crosstalk between channels and prevent mutual interference between amplifiers.

The volume regulator uses a resistor with a particularly low distortion factor. This resistor is mirror-finished and has low contact resistance and excellent abrasion resistance.
The brush that contacts the resistor is a gold-plated multi-contact type. It is integrated with the external terminal to eliminate the metal joint surface and reduce the strain caused by contact of different metals.
In addition, the rotation method is not a method in which the brush rotates, but a structure in which the resistor rotates by fixing the brush is adopted. This greatly reduces the internal contact points and eliminates the need for contact grease, improving durability.

The input selector uses AccuPhase's original logic relay control system that uses a sealed type relay containing nitrogen gas for the communication industry.
In this system, relays are installed where switching is necessary and controlled electronically by logic circuits. The precise timing is controlled by a microprocessor and there is no noise when switching.

It is equipped with a special amplifier for headphones, and the sound quality of headphones is also taken into consideration.
You can turn off the output to the speakers with the switch and adjust the headphone output with the main volume.

Comes with a remote control that allows you to switch the input source and adjust the volume.
The input selector is a relay switching system, and the volume adjustment is combined with a small motor with a clutch to prevent adverse effects on sound quality.

The C-250 has a line-only configuration, but the phono equalizer unit (sold separately) allows for analog recording.

Model Rating
Type Stereo Preamplifier
Frequency Response Balanced/Unbalanced Input : 20 Hz to 20 kHz + 0 -0.2 dB
Total Harmonic Distortion Factor 0.005% (at all input terminals)
Input Sensitivity / Input Impedance
(Rated Output / Output 0.5 v)
Balanced : 252mV/63mV/40k Ω
Unbalanced : 252mV/63mV/20k Ω
Rated Output / Output Impedance Balanced/Unbalanced Output : 2.0V/50 ohm
Tape Rec (at AD input) : 252mV/200 Ω
S/N
Input short, IEC-A correction (at rated input) Balanced:97dB
Unbalanced:119dB
EIA S/N Balanced:96dB
Unbalanced:97dB
Input Conversion Noise
(input short, IEC-A compensation)
Balanced:-109dBV
Unbalanced:-131dBV
Maximum power level (0.005% distortion factor) Balanced/Unbalanced Output:7.0V
Tape Rec (AD input) : 7.0 V
Minimum Load Impedance Balanced Output : 600 Ω
Unbalanced Output : 1k Ω
Tape Rec : 10k Ω
Gain Balanced/Unbalanced Input → Balanced/Unbalanced Output : 18 dB
Power Supply Voltage 100 VAC, 50Hz/60Hz
Power Consumption 9W
External Dimensions Normal : width 475x height 140x depth 401 mm
When adding AD-250 : Depth 414 mm
Weight Normal : 13.8 kg
When adding AD-250 : 13.9 kg
Sold Separately Dedicated Phono Equalizer Unit AD-250 (¥ 30,000)
Included : Remote Commander RC-10
Remote Control Method Infrared Pulse Method
Power Supply DC3V dry battery : UM-4 (IEC designation R03) 2 pieces
Maximum External Dimensions 66 mm wide x 175 mm high x 20 mm deep
Weight 190g (including dry batteries)