Accuphase DC-81
¥ 400,000 (released in July 1986)
Commentary
D/A converter released as a pair with the DP-80.
The D/A converter uses a current addition type and the DC-81 uses a discrete type to achieve a 16-bit theoretical limit.
An opto-isolator is used for electrical separation to prevent the adverse effect of high-frequency noise on the audio signal.
With the DC-81, the signal output from the digital filter is optically transmitted through 34 opto-isolators (with a transmission bandwidth of 7Mbit/sec). Each bit signal is then converted into an electrical signal and input to the D/A converter. This ensures complete electrical isolation and eliminates noise interference through conductors. On the board, the output of the opto-isolator passes through a mother printed board outside the shield frame and is input to an analog converter that is temporally and electrically shielded.
The digital filter is an independent double over-sampling type on the left and right. It is composed of 121 order filters, which have the highest order, so that the passband ripple, which affects sound quality, is within ± 0.001 dB, and the attenuation is -90dB abnormal (24.7 kHz).
The low-pass filter uses a discrete GIC type ninth order Butterworth active filter with carefully selected elements.
In addition, the output stage is only a buffer amplifier with a gain of 0 dB by setting the output of the converter according to the necessity of amplification. This circuit uses a push-pull DC servo directly coupled system to realize low distortion characteristics.
The digital input jacks are equipped with a total Route 3 of two dedicated optical fiber systems and one system for coaxial cable.
The bandwidth of the optical fiber receiver is 7Mbit/sec, which is the same as that of the transmitter faithful transmission and eliminating the radiation of high-frequency noise.
It is equipped with an emphasis circuit in order to support CD with emphasis applied.
The DC-81 emphasis circuit consists of a passive filter and a buffer amplifier.
The digital and analog circuits are shielded with metal, and the power supply is completely separated by a dedicated transformer.
In addition, the left and right audio circuits are laid out on separate printed boards to prevent interference between the left and right channels.
As a countermeasure against unwanted radiation, high-speed CMOS IC with less radiation is frequently used in digital circuits, and a line filter is used to prevent leakage through power supply.
There are two RCA phono jacks for output, one of which is fixed output and the other is variable output.
It also has an XLR-type balanced output.
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Model Rating
| Type | CD-only digital processor | ||||
| Formatting | CD standard format Quantization : 16-bit straight line Sampling frequency : 44.1 kHz ± 5 Hz |
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| Frequency characteristic | 4.0 Hz to 20 kHz ± 0.3 dB | ||||
| Total harmonic distortion factor + noise | 0.002%(1kHz) 0.008% (20 Hz to 20 kHz) |
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| S/N, Dynamic Range | 106dB | ||||
| Channel separation | 100dB | ||||
| Rated Output / Impedance |
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| Digital Input Format / Level | Formatting : Digital Audio Interface Optical : Received power from -15dBm to -28dBm Coaxial : 0.5Vp-p/75 Ω |
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| Semiconductor used | Transistor : 66 FET : 8 IC : 68 Diode : 44 pcs |
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| Power supply voltage | AC100V/117V/220V/240V, 50Hz/60Hz | ||||
| Power consumption | 25W | ||||
| External dimensions | Width 475x Height 135x Depth 373 mm | ||||
| Weight | 15.5kg |