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Reference-7.1(Since Jan. 2011)
Dedicated Discrete Fully Balanced DAC

DSP-1 inside
Built in 8 Pieces  PCM1704UK Chips

Price:      (Exclude shipping cost)
               Non-USB version USD1900
               192KHz USB version USD1960

DSP-1 Device Characteristics：
　

Devices Characteristics:
Two-channel Digital Interpolation Filter and data in-phase processor for digital audio.
208-pin PQFP package, Manufactured on 300-mm wafers using, 90-nm low-k dielectric process. Devices offer advanced features for high-performance digital signal processing (DSP) applications with up to 250-MHz.
Data and Master-clock in-phase processing just without jitters.

Filter Configuration:
Core power supply voltage: 1.2V.
I/O power supply voltage: 3.3V.
Programmable Functions: hardware control mode.
Two-channel 1-times / 2-times / 4-times / 8-times oversampling , supports Bypass mode (NOS mode.).
Three-stage linear-phase ( group delay distortion : Zero)  FIR filter configuration.

Filter Characteristics:
Stopband Attenuation: –50dB / -90DB / -130DB.
Passband: 0∼0.4535Fs.
Passband Ripple: within ±0.00001dB.

 Input/Output:
Input Data Formats: I2S
Input Word Length: 16, 20, or 24 Bits
Output Word Length: 16, 20, or 24 Bits
Output Data Formats: MSB-First, Binary Two’s Complement
Sampling Frequency: 32kHz to 96kHz( In DAC Reference One/Two , because they Applied DIR9001 receiver chip, so only Supports 24 Bits, 32-96K)
Supports 24 Bits, 96 kHz Sample Rate
 
Master-Clock:
Clock Autodivide Circuit Supports four Master-Clock Frequencies : 256Fs、384Fs、512Fs、768Fs
Built-in two groups high performance PLL , supports low jitter Master-Clock output.

Transition Characteristics（-130dB）

Passband Characteristics（-130dB

About ACSS:
     ACSS (Audio-gd Current Signal System) is Audio-gd's system for transmitting audio signals in the current domain. This concept, first seen in 1966, we have used for many years, and since 2005, have evolved the technology to include all audio signals in our systems from the digital source to the power amplifier. Since 2006, ACSS comp5nts have become Audio-gd's most popular products.

ACSS:     
              The Reference-7.1 is a real fully balanced discrete design. Applies the 8 Pieces Expensive high-end grade PCM1704UK which can support up to 24Bit/96KHz input . Similar to other PCM1704UK designs , we applied Non-feedback ACSS analog stages. The 8 pcs PCM1704UK feed to the ACSS analog stages without any OPAs and couple caps so it can avoid sound coloration .
              The ACSS is a non-feedback technology made with fully discrete amplifiers. Most people know the global feedback design can offer better specs in test measurements, and classic non-feedback can't do well in test measurements but can offer better sound for the human's ears. Here is a conflict of the classic circuits. But the ACSS opens a new field, it can offer a least coloration sound which is more neutral with very low distortion and high linearity. So it can retain the dynamics, detail and neutral sound but not sound bright or harsh.
Output buffer:       
    The output buffers are Non-feedback. For low impedance, we applied the dual FET buffer output stage which is quite less colored than most conventional circuits.
DSP-1 processor:
           DAC Reference 7.1 has built in DSP-1 processor, which is a Two-channel Digital Interpolation Filter and data in-phase processor for digital audio. This Device offers advanced features for high-performance digital signal processing (DSP) applications up to 250-MHz. Data and Master-clock in-phase processing are without jitters. So DAC Reference 7 can offer a clear and focused soundstage, apart from accurate and neutral reproduction of the recorded disc/music.
           Theoretically when using the DSP1, data will be running parallel, achieving near zero jitter state, but degrade on sound quality not only the jitter, there are some lot reasons can effect the sound quality, so better source sound better.  But the DSP-1 can process the data better than typical digital processor chip like PMD-100, DF1704 etc, through some experiment, although we could perceive the sound quality difference between differently priced and level of sources ,  final result shows that using entry level CD transport or hypermarket grade DVD player, the improvement of sound quality is huge compared to  PMD-100, DF1704 etc.

Power supply:
            Reference-7.1 applies the excellent 8 pcs PCM1704UK and excellent analog output stages, but these are not the only keys of the best sound. The power supply is most important. Even applying the best DA chip and the best amp, if matched to a normal power supply, the total sound may still be average or sound musical, but can't be neutral and detailed. That is why it is easy to find hi-end grade gears maybe without the best chips or amp stages, but with plenteous dedicated DC supply circuits.
            The Reference-7.1 had total 21 PSU groups are applied. Uses 19 groups of high-quality class A parallel connection PSU with dedicated DC supply double-stage PSU, which can offer very clear DC power for the DAC, producing a very black background and neutral sound characteristic. The double-stage PSU is very important for digital parts. Some designs may have very low jitter in theory, but if the power is supplied by a dirty or low-speed power supply, it will increase the jitter and pollute the data, and degrade the sound quality obviously.
             The class A parallel connection PSU has very high input impedance to avoid pulse through the PSU from affecting the DAC and low output impedance with very fast speed and high linearity, so it is a very clean power supply. In my experience, its sound is better than battery power supply, better human sound and neutral.