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Even though the PCM1704 PDF declare the PCM1704 support up to 96KHz / 24bit, highest word clock input is 768KHz.
In fact the PCM1704UK can support 192KHz / 24bit at 8X oversampling (USB or I2S model), the word clock input is 1.536MHz , as high as ESS9018.

Reference-10.32]USB applied USB-32^
Discrete  DAC + Headphone amplifier / Preamplifier

Built in DSP-1 data processor
32bit / 384K Asynchronous Transfer  USB-32 Chip
Built in 4 Pieces Hi-grade PCM1704UK Chips

wires and TCXO built in



Summarize Use Manual Specs Technology Detail Custom Option Shipping Cost

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:
V50dB / -90DB / -130DB.
Passband: 00.4535Fs.
Passband Ripple: within 0.00001dB.

Input Data Formats: I2S
Input Word Length: 16, 20, 24 or 32 Bits
Output Word Length: 16, 20, or 24 Bits
Output Data Formats: MSB-First, Binary Two
s Complement
Sampling Frequency: 32kHz to 192kHz

Supports 24 Bits, 192 kHz Sample Rate
Clock Autodivide Circuit Supports four Master-Clock Frequencies : 256FsB384FsB512FsB768Fs
Built-in two groups high performance PLL , supports low jitter Master-Clock output.

     Transition Characteristics]-50dB^

     Passband Characteristics]-50dB^

    Transition Characteristics]-90dB^

Passband Characteristics]-90dB^

Transition Characteristics]-130dB^

Passband Characteristics]-130dB^

Detail of the Current Conveyor (ACSS) Technology

            The Reference 10 applied real balanced fully discrete amp without any OPAs (the OPAs in Reference 10 only for DC serve) ,without any couple caps ,fully non- feedback . Applies the 4 Pieces Expensive high-end grade PCM1704UK which can support up to 24Bit/96KHz input . Compare to other PCM1704UK designs , we applied Non-feedback ACSS analog stages. The 4 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.

Applies the 4 Pieces Expensive high-end grade PCM1704UK . The PCM1704 UK had been consider the best neutral and "sound like real " DA chips by a lot hififolks, but TI want to discontinued PCM1704 and  increased the price to USD48/pc  , cause the market price increase to USD70/pc .

Output buffer:       
            The output buffers are Non-feedback. For low impedance, we applied a diamond output stage which is quite less colored than most conventional circuits.
             The analog part is without couple caps to avoid coloration, and power supply by four groups class A PSUs.
             Applies ACSS technology, even though maybe you only connect to XLR or RCA output, Reference 10 will always operate in ACSS technology, and benefit from ACSS technology. Therefore, XLR and RCA output will also definitely bring about improvement in sound quality. Even through RCA output, the 4X PCM1704UK DA chips will perform fully.
DSP-1 processor:
Applied the DIR9001 as the SPDIF interface , even though it only support up to 96KHz /24bit, but  its sound characteristic had been consider most neutral by a lot hifi fans , the jitter only 50PS, much less than the CS8416 ( 200PS ).
             DAC Reference 10 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 10 can offer a clear and focused soundstage, apart from accurate and neutral reproduction of the recorded disc/music.The DSP-1(V5) digital processor can supports NOS, 2X, 4X and 8X oversampling customers setting, and keep the timing more steady.
            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 10 applies the excellent 4 pcs PCM1704UK with DSP-1 combo and excellent analog output amps, 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 10 uses 8 groups of high-quality class A parallel connection PSU , which can offer very clear DC power for the DAC and amps, producing a very black background and neutral sound characteristic. The class A  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.
             The Reference 10 uses three high performance transformers. More than 50,000uf audio grade NOVER capacitors are used to ensure ample and smooth power feed. A total of 8 groups class A SPUs and 3 groups linear PSUs are used to purify the power supply. To achieve high S/N, the control circuit is powered with separate regulator.

Volume control:

           The volume control is also different from conventional technology. Conventional volume control technology is the volume control implement in the analog amp input stage through a volume pot to reduce the signal  . The volume pots quality effect the sound quality direct , the low quality volume pot cause lost the detail and channels imbalance cause the soundstage distortion  . Even the high performance volume pot still cause the detail lose. Whatever quality volume pots, must cause the S/N worst .
       But in the Reference 10.32 , we applied the I/V conversion volume control , the volume control just  a variable passive I/V conversion place at the ACSS amp output , where the output is the current signal, not the voltage signal. The volume control is I/V conversion, and the volume depends on the current (I) conversion to the voltage (V). (Like R-2R D/A chips output passive I/V conversion)  It can keep the signal frequency band flat and not lost any detail.
It can't degrade on sound quality in every volume level . After the volume , there are four groups  diamond non-feedback buffer output stages offer the very low output impedance  .
            Mark Levinson also knows that current volume control has great benefits, so in their Top End preamp NO.32 volume control, they use many components to change the signal to current signal (I), then implement the volume control , and then change back to voltage signal (V) again. But Reference 10.32 is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology. The less conversion bring much neutral sound .
            The volume control quality is much important in the real balance gear . It must guarantee the four channels signal control exact to achieve the performance of the real balance gear .  If the cool and hot of the balance signal can't guarantee exact, the balance output will has large distortion cause the sound quality and performance even much worst than a single end gear waste the  balance gear  design and the cost.
            In Reference 10.32 is applied a four channels digital control relays based volume control. .Reference 10.32 has total four channels through changing the DALE resistors to control the volume for avoid channels imbalanced ,achieve the best performance and sound quality of the gear.
           Reference 10.32 have 100 steps volume control, control range achieve 90DB (usually the steps volume ports, potentiometer volume port, relays base volume control all have around 70DB range  ), very smooth control range on first 50 steps , cooperate with 13DB high gain, so can very easy adjust the volume for  both high / low sensitivity headphone and speakers. While users change the volume, the different relays break or close, it may had slightly switch sound on output and disappear while stop change the volume.
Supper Exponential volume characteristic        The Volume steps comparison to normal volume knob       

            Reference 10 has complete separation of left, right amplifier channels, power supply, and transformer.
             Reference 10 uses heavyweight all-aluminum alloy chassis to prevent the eddy current of transformers from interfering on circuit board. 
            Reference 10 applies optical couple isolation for the MCU and the control implementations to prevent the MCU affecting the audio parts.

Static storage mode control software:
           In most control softwares design, the MCU will continuously output data to the perform parts , the MCU had the very high speed, so the output data become high frequency impulses disturb the audio signal circuits make the sound worst . This product had applied static storage mode control software , the MCU output once control data and save in the perform parts while just power on and users operate ,then stop output data until users next operation. This design make the sound quality improve on the clear and transparency .



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