Elektor DAC2000 Build Using AD1865 DAC

The curiosity I got from studying the DAC2000 schematic that I previously post are on the analog stages.

Although this analog stage is quite common for the third pole LPF, but the specific resistors value become the key factor for the overall LPF slope result. The goal for a better LPF calculator is we want the slope of the LPF as linear as possible because it reflect to the sound quality.

That is why I want to make the same DAC2000 but with some changes, especially on the DAC section that will be using AD1865.

So let's continue.

This DAC2000 build will be based on AD1865 DAC and SM5813 digital filter instead of PCM1704 and DF1704.

The reason why I am not build it based on the DAC2000 schematic is because I don't have DF1704 on hands, but instead I will replace it with SM5813. The other reason for the AD1865 DAC will be use in this build is because I was familiar with the sound from this DAC IC. I can easily find the difference when using the DAC2000 analog stage in this AD1865 DAC build.

The connection between AD1865 and SM5813 are explained on the AD1865 datasheet which I will not repeat here. Then the rest of the section will be using exactly the same as the original DAC2000 schematic except for the hardware control, external reference clock and frequency sampling display are eliminated.

To make this DAC2000 AD1865 DAC easy to understand, I modify the original diagram as shown in the picture bellow.

Only the yellow block are replaced, other than that are all the same.

I start with the power supply build first.

As usual, the power supply components are all common using diodes, capacitors and regulators. The voltage regulators are combined between 5 volt fixed regulator for digital section, the 12 volt differential for analog stages and the LM317/LM337 adjustable regulator are set to 6 volt differential output specifically to supply the AD1865 analog stages.

The 6 volt differential power supply for AD1865 DAC are too high and possibly damaging the IC but the reason why I choose 6 volt because on the DAC board next to it will be another voltage regulator using TL431 shunt voltage regulator to drop the voltage input to become 5 volt. The reason using multiple voltage regulator are to obtain better power supply noise performance.

Now I continue the build to the DAC board.

The first things to do is populating the components for digital receiver using CS8412 and digital filter using SM5813.

Now I start to build the analog stages.

But before going to the building process, let's take a look closer to the DAC2000 analog stages schematic first.

On the original DAC2000 schematic, there are two LPF section that can be switch automatically based on the hardware control from the digital receiver signal.

The orange box above is the 3rd order Butterworth filter configuration with cut-off frequency on 27 kHz for most usual sampling rate: 44.1 and 48 kHz. This the most common sampling rate for music playback.

The blue box is Bessel filter configuration with cut-off frequency on 44 kHz for higher resolution audio: 88.2 and 96 kHz.

Since my original music source are all from CD's, so I just making this LPF based on the orange box schematic above.

The DAC board is now finished and the rest of the steps are just connecting between those PCB.

Back to the multiple voltage regulator I mentioned before, this is the closer look of the TL431 IC in DIP-8 package.

I using 22 ohm series resistor for 50 mA current sink, then the adjustable resistors are 2 pieces 1000 ohm, regulated from the 6 volt input to 5 volt output.

This TL431 voltage regulator are placed very close to the AD1865 voltage input pins.

The AD1865 using in this DAC is the K grade which is the highest grade.

The op-amps are all original OPA627.

So how is the sound quality?

In my opinion, the oversampling AD1865 using DAC2000 analog stage is very clean. Probably will win for any DAC measurement test.

This DAC sound open with good detail and dynamic. The nature of the multibit DAC sound which are warm in mid-range are still there but just like combination with the sound of Delta Sigma DAC which are mostly very clean.

I think this might be not my "cup of tea" DAC, but I am quite satisfy with this overall DAC performance.

At least my curiosity for using DAC2000 analog stage are now paid off.

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