In this part 2, I will focusing on how to connect from the digital receiver IC to the digital filter IC. This part 2 is continuing from the Part 1 which explained how to convert from SPDIF CMOS to TTL digital format required by the YM3623.
At the glance, you might wondering why I prefer the over-sampling instead just a simple non-oversampling glue-logic? And this where the fun begin. The fun why I am refuse the dogma that always told you for the non-oversampling is the best sound quality compares to the oversampling.
Theoretically the oversampling is required to smoothing the ladder steps on the frequency band created by the digital domain. Ok, I a not going to much technical, but this oversampling is required for the smoother overall audio frequency response. The oversampling also reducing the complexity in the low-pass filter at the analog section. The result for this oversampling is better audio performance in all audio frequency band.
If you familiar in building a DAC before, the simple one is build a non-oversampling DAC. This approach mostly suffer for the fuller music presentation. It is more emphasis on mid-to-low frequency and attenuate the details. This also creating an illusion that the DAC in non-oversampling give more natural and warmer presentation.
Another problem occurs when the glue-logic that mostly using in the non-oversampling DAC is use to divide between the right and the left channel (except for I2S required by TDA1541 or TDA1543). This is basically inverting one digital signal required by the DAC IC to determine the audio channel, while the other is not. This glue logic process will resulting in time alignment differentiation between both channel. Although this difference is so small and can be obey in the real listening test, but at least you know that this is not completely correct in the implementation.
All commercial CD player or DAC built by the big name in audio, both hi-end or mid-class are all in the oversampling method. The problems with the oversampling that can cause the sound quality worsen is because the quality of the digital filter itself.
Because what I stated in the part 1 on my ultimate DAC build here is theoretical all the best, so I will using this oversampling mode with the best measurement on the digital filter IC itself.
But before I reveal the best digital filter for this project, let me brief a little bit about digital filter in general.
I had use the SM5813 in my PCM63 and AD1862 DAC build here and here. The schematic is also available on that link. This SM5813 is use on many hi-end CD player and the application is quite simple. The others reputable digital filter is PMD100 and PMD200. Those are HDCD compatible and respected by audiophile to become one of the best digital filter to date. The others digital filter that simple but also good are YM3434 or DF1704. Those are good digital filter that should be use for better sound quality in oversampling DAC.
In this ultimate build, I am using CXD1144. This digital filter IC is manufacture by Sony and become the rarest, yet expensive digital filter IC at that time. This CXD1144 is also mentioned by Stereophile magazine to become one of the best and the most taps in digital filter domain. The article about this is written when Stereophile magazine released the Kinergetic Research KCD-55 Ultra DAC review.
What so special about this CXD1144?
By looking to the diagram about what inside this CXD1144, you can see there is 2 digital processing in parallels, each are 22 bit digital processing. This method is unusual which you may never seen before in other digital filter. This approach resulting the best ripple rejection, about 0,00001 dB and stop band attenuation under -120 dB. This is a great number accomplishment which no others digital filter can reach this number so far.
The downside to this CXD1144 is only limited to either 16 bit or 18 bit output. No 20 bit option here. Because the complexity of this internal CXD1144, the result is this digital filter draw more power compares to the others. It need power dissipation about 500 mW.
So enough with the introduction, lets continue to the schematic.
The first things that need to explain before going to the CXD1144 is the components on the digital receiver YM3623.
YM3623 is the digital receiver. The pin 28 is the TTL digital input from what I discuss in the part 1.
Then I focusing what external components need to run this YM3623 which is only at pin 1 to pin 8.
Especially on pin 3 is the filter network by using a resistor and a capacitor. The value as per datasheet is quite flexible and in this case I using a 220 ohm with 6,8 nF.
Jump to the pin 7 is the VCO required by the YM3623 to reset once it powering ON. It need always a positive voltage but in series with a 100 nF. The value for the resistor is also flexible. The datasheet confirm the value is should be 5k ohm + the resistor on the filter on the pin 3. In this case I can use 5,2k ohm or just like on the schematic I am using 4,7k ohm which also working fine. Looking to the most application out there, I saw this resistor value can be as high as 17k ohm.
The other external components required by the YM3623 is on the pin 4 and 5. They are connected to the external crystal, again the value is also flexible because this crystal only works when there is no present signal from DIN. In this case I am using 16 Mhz.
The schematic above is the connection pin from YM3623 digital receiver to CXD1144 digital filter input pin. For clearer schematic, please mention the pin connection on the CXD1144 to the ground or to the +5 volt is the requirement by the datasheet. Those pin can be share with the YM3623 as well.
Except for pin 13, 15, and 17 is determined for mode selection on each input and output option. In this case I am using 8 times oversampling, 16 bit input and 18 bit output in binary 2 complement data.
Pin 7 in CXD1144 is shared the same function as pin 7 in YM3623. So I tie them together without adding any additional components.
The schematic above is the full connection diagram between the YM3623 to the CXD1144. It is 18 bit data format required by AD1865 DAC. The CXD1144 required almost no external components except additional smoothing capacitor on the input volt pin 8, commonly only using 100nF (not shown in the schematic). By this diagram you are now successfully makes them work together.
Please note that schematic above are 100% drawn and design by myself after reading the datasheet. Although I also have the Kinergetic Research KCD-55 Ultra DAC that have the same digital receiver IC, but both of them are different in the implementation.
In the next post, the part 3, I will share the connection between the CXD1144 and the AD1865 DAC IC. So stay tuned.
Disclaimer: Any statement and photos in this article are not allowed to copy or publish without written permission from the writer. Any injury or loss from following tips in this article is not under writer responsibility.
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