PCM1704 XA2 Fever Stereo Audio Decoder
XA2 DAC decoder with 4 R2R PCM1704 decoder chips Mono dual output. The sound of the XA2 is far from ordinary, and the full-band interpretation is gorgeous and noble.
XA2 Design Overview
From the beginning of conceiving this design project, after a year, the sound quality of the well-received PCM1702x4 OP MK2 and the design architecture using S8 (TDA1541), using the power supply and DA split architecture, reduce the slight vibration of the power transformer when working. For the influence of sound harmonics, the digital receiver adopts the CS8414 which has the expressive power of Crystal Company to receive. The digital filtering adopts the DF1704 with the PCM1704 and the digital filter DF1704 to achieve seamless connection. The DF1704 works in the oversampling state of 8X 256FS, reducing Distortion and support for 24BIT 96K. A true voice, the performance of the three segments of the sound is balanced, but this real voice is generally not acceptable to the human ear. In view of this, we start from the sense of hearing, and at the stage of tuning, we should add some positive improvements, such as increasing the thickness of the intermediate frequency, and modifying the Q value of the LPF to attenuate the high-frequency cut ear sound. For a hearing-resistant device, it has enough resolution, transparency, density, low-frequency thickness and good sound field depth, which is what every player pursues. The overall sound quality of the XA2 can be described in terms of noble atmosphere. The original intention of using the PCM1704 chip is that many customers have made good requests. To meet this requirement, we have not chosen the cheap and easy to purchase PCM179X series, CS439X, AK4xxx series DA or the same level ES9018, 9028, and directly used R2R's oldest chip PCM1704 has obvious advantages for musical performance. In order to achieve the required sound performance, a large number of audio components, WIMA, ERO, ELNA and other audio capacitors, PHILIPS VISHAY 1% high-precision resistors are used. Although the XA2 coaxial fiber only supports 96K sampling, it can support up to 192K after adding a USB module. Supports playback of audio files in mainstream formats such as WAV, APE, and FLAC. WAV, APE, FLAC and other audio format files are diversified. The XA2 provides an upgraded USB interface for easy connection to PCs and mobile devices. The sound is good or bad, can't use any DA chip from the machine alone, what kind of fever component is used, more important is the overall design of the PCB, including layout, signal direction, etc., subdivided, subdivided into PCB trace These are particularly important for the mutual interference of component ranks. The XA2 is carefully considered in these design details and follows the design rules. With a good design foundation, the current price XA2 has an unbeatable price/performance ratio, and the sound direct PK is 2-3 times its value. We have this confidence.
The PCM1704 is an R2R-based DA chip that integrates a Bi CMOS signal architecture to eliminate bipolar zero nonlinearity. A 24-bit R-2R step-current DA conversion structure that uses precision resistors to create a precision current source that provides wide dynamic range and ultra-low distortion. The PCM1704 is a current output type D/A, which improves the output signal immunity and provides users with more analog design options.
The PCM1704 uses a +5V supply and provides an inverting pin with very low power consumption due to its internal design. It was used extensively on those classic CDs or DAs of the year, such as Mark Levinson, Pu Shi, Mai Jingtu, CARY, Yiya, KRELL, Japan's Golden Dice, and so on. The current price of these machines is still high.
XA2 sound features:
Noble and gorgeous full-band performance, large dynamic sound field construction, medium-high frequency over silky smooth, clear sound image, high-density detail reproduction, low-frequency solid and thick.
Official version of the package sales:
Package 1: PCM1704 XA2 PCB+ resistance kit. This kit only contains 2 pieces of PCM1704 XA2 circuit board (power + D / A) + matching resistor package. The resistors are all taped PHILIPS 1/4W 1% high precision metal film resistors. The power board is also available with a separate power strip for switching to different transformers.
Package 2: PCM1704 XA2 standard kit. This kit does not include the PCM1704*4 chip and does not include a power transformer + chassis. All other components are included
Package 3 (selected blue): PCM1704 XA2 finished board. This kit contains 4 PCM1704 chips. Does not include power transformer + chassis.
PCM1704 XA2 making a real shot:
Production & Debugging:
1. Because the D/A board has no power supply design, you can make the power part first after you get it. Because the PCM1704 is expensive, after the welding is completed, after the check is correct, the power test can measure the normal voltage of each group before you can access the D/A. The power board provides 6 sets of DC output, and the output voltage must be the same as the on-board label. U205 (7915) does not need to be welded.
2. The board is designed with two dial switch switches. The switch to the digital balance input is close to the 2P socket (ON: ON=AES/EBU), and the switch to the I2S input is close to the 5P socket (ON: ON=I2S) IN). After the production is completed, the two switches are not connected, the default is coaxial or fiber input.
3. When the power board and the D/A board are connected, the soldered socket can not be reversed. After the completion of the production, it is necessary to check the key. If the power cord is not connected, there is a danger of burning the IC!!!!!
4.XA2 uses two sets of AC voltage: a set of dual 15-18V, a set of dual 9-12V integrated power board design using TALEMA 15-25W transformer, directly soldered on the PCB. The independent power board and the integrated power circuit are exactly the same, except that the installation position of the transformer is omitted and more transformer options are accommodated.
5. When the heat sink is installed, it can be installed without insulation, because the PCB is already designed to avoid it. Will not cause a short circuit. Thermal grease can be added
6. The polarity of the electrolytic capacitor can not be mistaken. Small capacitors cannot be installed incorrectly, especially the 47N (0.047UF) capacitor of the CS8412 PLL pin.
7. Make D/A, you can solder the patch first, CS8414, DF1704, PCM1704
8. More gameplay: PCM1704 XA2 Because it is a two-way structure design, you can use 2 or 4 PCM1704. Just change the IV resistance accordingly.
debugging:
1. Check the test power supply. After the whole machine is welded, carefully check the installation diagram. Check to ensure no error components, short circuit, and virtual soldering. After checking the problem, first debug the power board and pass the voltage corresponding to the (input transformer). The measured DC output must be the same as the PCB label. The +-15V of the analog section can be fine-tuned to adjust the output voltage to +-15V.
2. Digital part: 3 groups + 5V, 1 group - 5V. Analog part: (discrete power supply) 1 group +15V, 1 group -15V (adjustable to +-15V)
3. Voltage measurement: After the power supply test voltage of a single power supply board is normal, connect the D/A board with a wire, and don't busy plug all the ICs first. At this time, test the power supply board output voltage correctly (the voltage test point on the power supply board, output) Beside the socket), test all voltages without change, if there is a change, there must be a short circuit, you must find the exclusion.
4. DF1704 27 feet is SR0, this foot is to adjust the slope of the digital filter, the external connection is CN106 socket. After the fabrication is completed, the solder is shorted to the two points of 27, H.
5. After power-on, the IC should not have overheating. At this time, the RCA output can be tested with a multimeter. The normal output is DC-free. At this time, you can access the signal and listen to it normally.
6. Special Note: When powering up, do not plug in the power cable between the power board and the D/A board. Due to the contact time error, the op amp will be inverted to the decoder chip and cause damage.
Design conclusion
The PCM1704 is a large-scale DA of the R2R architecture. The XA2 has a rogue listening experience and cannot be missed.
