Accuphase DC-300
¥980,000(Released in November 1996)
Commentary
Based on advanced digital technology, this digital preamplifier was developed for the first time in the world by combining new circuits using high-speed DSP technology.
The coaxial and optical input terminals can receive digital signals of up to 24 bits at sampling frequencies of 32/44.1/48kHz.
Audio Interface) decoder automatically locks the sampling frequency, and the high-precision 44.1/48kHz, level I input signal uses an ultra-jitter-free PLL circuit to extract the master clock without pulse transmission distortion or jitter, and serves as the system reference.
All other low precision signals are converted to 48 kHz, level I signal by SFC (Sampling Frequency Converter) before clock extraction.
The DSP (Digital Signal Processor) is used for digital processing of tone control, compensator and monophonic phase switching functions which are heavy for a preamplifier.
Then, the signal whose sampling frequency is converted to 8 times by the digital filter is used one by one for one channel and entered into the ultra-high-speed DSP. Here, the digital gain control by the special noise shaper process adjusts the volume to -95dB with little degradation of sound quality. At the same time, the DSP processes the balance adjustment and attenuator.
An ultrafast optocoupler is then used to electrically separate the digital and analog sections completely.
It is converted to an analog signal by a Multi-Bit) D/A converter, cut by a fourth order analog filter and output.
The volume adjustment section is equipped with a digital volume developed using special noise shaper processing technology.
A special noise shaper processing technique using a digital signal processor (DSP) can reduce the noise level in the audible band to the theoretical limit. Therefore, the digital time-division feedback of the data which is lost bit by the noise is improved to the resolution higher than the D/A converter.
Equipped with digital volume control with analogue operation feeling.
A disk with radial slits is attached to the shaft of a large knob. When the disk passes through a phase detector, a pulse is generated, and this pulse is input to a microcomputer to adjust the volume.
This has been further developed into a high-quality volume by thoroughly pursuing matching of the sense of rotational speed and sound quality change.
With DSP tone control and compensator, only the frequency can be changed, making it possible to control the sound quality without changing.
The D/A converter uses the MMB method D/A converter.
In the MMB method, a large number of carefully selected 20bitD/A converters (8 per channel in the DC-300) are driven in parallel. The high-speed output of an 8 x oversampling digital filter is input to all converters, D/A converted and added.
This matches the phase at higher frequencies and improves performance at all frequencies and signal levels.
Ultra-jitter-free PLL (Phase
Locked Loop) circuit to extract the master clock which is the system reference.
The ultra jitter-free PLL circuit includes a preamble signal (marker indicating the head of the LR signal) detection circuit and a VCO (Voltage)
The master clock extracted by this circuit is not affected by jitter and pulse transmission distortion.
In order to up-convert the sampling frequency to a higher frequency once and resample at the desired frequency (48 kHz, level I), SFC (Sampling
Frequency Converter).
The Oversampling Digital Filter has a 20-bit 8 x oversampling digital filter.
The analog filter is a 4th-order Butterworth filter. This filter circuit optimizes the cut-off frequencies to minimize phase rotation in the passband and is combined with carefully selected elements to improve sound quality.
Using a high-speed optocoupler with a transmission capacity of 40 MBPS, the digital and analog sections are completely separated. The high-speed transmission characteristics allow the digital signal to be transmitted to the analog section without noise.
The display of the input position can be changed. It is possible to change the name to the name stored in advance, or to create a unique name by combining 8 letters from 96 kinds of letters and symbols.
The analog output consists of a fully balanced circuit floating from ground.
The output jacks have balanced XLR and unbalanced RCA connectors.
The optional board slot allows analog inputs and outputs to be operated in the same way as a conventional preamplifier using an ADB-compliant option board.
The analog input is converted to a digital signal by an A/D converter on the board and to an analog signal by an D/A converter on the board.
In addition, a line input board is mounted as standard.
Model Rating
Type | Digital Preamp | ||||||||||||||||||||||||||
Input Format (EIA standard format) |
Quantization : 16-bit to 24-bit line Sampling frequency : 32 kHz, 44.1 kHz, 48 kHz (automatic detection) |
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Digital Input Format Level (EIAJ CP-1201) |
Format : Digital Audio Interface Optical : optical input -27dBm to -15dBm Coaxial : 0.5Vp-p/75 Ω |
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Digital Output Format Level (EIAJ CP-1201) |
Format : Digital Audio Interface Optical : Light output from -21dBm to -15dBm, emission wavelength 660 nm Coaxial : 0.5Vp-p/75 Ω |
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Frequency Response | 4.0 Hz to 20 kHz ± 0.3 dB | ||||||||||||||||||||||||||
D/A converter | MMB, 20-bit | ||||||||||||||||||||||||||
Digital Filter | 20-bit, 8 x oversampling | ||||||||||||||||||||||||||
Total Harmonic Distortion Factor | 0.002% (20 Hz-20 kHz) | ||||||||||||||||||||||||||
S/N | 122dB | ||||||||||||||||||||||||||
Dynamic Range | 112 dB (24-bit input, LPF : off) | ||||||||||||||||||||||||||
Channel Separation | 112 dB (20 Hz to 20 kHz) | ||||||||||||||||||||||||||
Output Voltage / Impedance | Balanced : 5V/50 Ω, balanced XLR type Unbalanced : 5V/50 ohm, RCA phono jack |
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Volume Control (DSP) | Speed sensing rotation method 0 ~ -95dB Step Variable (0.1 ~ 5 dB Step), ∞ |
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balance control (DSP) | Speed sensing rotation method Difference between right and left : 0 ~ -95dB step variable (0.1 ~ 5 dB step), ∞ |
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Tone Control (DSP) |
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Compensator (DSP) | +6dB(100Hz) | ||||||||||||||||||||||||||
Attenuator (DSP) | -20dB | ||||||||||||||||||||||||||
Power Supply | 100 VAC, 50Hz/60Hz | ||||||||||||||||||||||||||
Power Consumption | 25W | ||||||||||||||||||||||||||
Maximum External Dimensions | 475 mm wide x 150 mm high x 406 mm deep | ||||||||||||||||||||||||||
Weight | 21.5kg | ||||||||||||||||||||||||||
Attachments | Line Input Board AI-U1 Remote Commander RC-19 |
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Sold Separately : Option Board | |||||||||||||||||||||||||||
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