DAC

digital-to-analog converter

The sound will begin here

There are two types of music lovers today, some listen to vinyl records, others use decidedly expensive converters to listen to CDs, music files or simply streaming music contents.
The reason is quickly found when listening comparisons are made and it is found that one of the most important factors influencing the sound is the pre-amplification, i.e. directly behind the D/A converter or integrated in the D/A converter.
From the part of the industry, converters and preamplifiers are primarily offered in unnecessarily minimalistic quality, so that the DAC presented here only gets its raison d'être from this market situation.
IFrom the part of the industry, converters and preamplifiers are primarily offered in unnecessarily minimalistic quality, so that the DAC presented here only gets its raison d'être from this market situation.
In the upper mid-price segment, D/A converters are often based on high-quality chip solutions, such as the TI Burr-Brown PCM5122. This is just right for a loudspeaker like the printed ball speaker, but if loudspeakers with a high level of precision such as the Совершенно or the Beatbox are to be used, then a significant amount of detail, low distortion (especially in the bass) and the fine detail required for the acoustic scene are missing. The DIY-DAC is able to play such details despite its low cost. This makes it an excellent analogue source that can easily compete with other high-quality analogue sources. 

The DAC presented here is no longer available and therefore a new DAC based on the Texas Instruments PCM1794A was built and optimized.

The DAC introduced here is electrically divided into three segments, each of which is separately supplied with power. This design is a major difference to many other DIY-DAC boards. The DAC uses an AK4495seq as D/A converter for studio mixing consoles. A preamplifier is connected to this component, built with a 2-channel op-amp. In front of the D/A converter is the control unit, on top in the picture it is an XMOS USB. 

The basis of the DAC are boards from China, which are available with USB as well as with Coax or Toslink. The circuit boards can be recognized by the slightly component-intensive circuitry of the preamplifier, as this circuitry causes a significant difference in the signal output/quality. Also the power supply with several transformers is important for the high resolution function of the OPamp.
Board with USB connection: not available
Board with Coax and Toslink: not available
The assembly of the board of the DAC is good in relation to the price. There was already a board with a cold solder connection, which had to be re-soldered first, this is included in the price. The component values are not always the same as the printed ones and so there is still a bit of tuning potential. There is also still a little bit of potential on the component quality level. But the positive thing is that the quality of the PCB assembly is so good that even with the Analog Devices OP the DAC sounds very good. The sound quality can be further enhanced by the TI Burr-Brown OPA1656 soldered on an adapter as shown in the picture. This operational amplifier exceeds the usual and shines with an undreamt-of natural reproduction. Compared to the AD827, another veil falls from the speakers and the emotionality of the sound presented increases even more.

The power supply

First of all, it should be noted that the rules applicable in the country in question for the construction of high-voltage circuits must be observed.

For the DAC there is a very simple power supply with not so common filters.

After the fuse and the power switch a DC filter is shown, which blocks DC voltage with 8 diodes (SF26G) and some capacitors. The two 220nF capacitors in combination with the printed transformers cause the reactive current to be close to zero during operation and the crossover works perfectly: Via the transformers the mains signal - i.e. the 50Hz AC - is conducted and via the capacitors high frequency disturbances in the power network are short-circuited - i.e. reduced. To ensure that this works well, I use WIMA FKP1 capacitors with high dielectric strength.

The following is a list of components for the circuitry of the DAC boards: 

DAC Tuning:
The end is not yet reached with such a DAC board, because there are low-loss capacitors on the market, which bring a bit more air into the sound, to speak in pictures. This is in fact rather cosmetic, but also a kind of rounding up, so that the OPA can work optimally. 

This involves replacing the capacitors around the operational amplifier. I soldered in the values printed on the board and used WIMA FKP2 as quality. The capacitors with higher values have to be chosen in a low dielectric strength, because otherwise they have no place on the board. I replaced the two 47μF electrolytic capacitors by Panasonic EB A (50V), beside it I replaced the 100nF by Wima MKP2 (250V). Also for the power supply of the AK4495seq you can think about replacing the 100nF capacitor, there is also space for a bigger MKP.
Finally the normal diodes were replaced by Scotty diodes Vishay type SB1H100-E3.
The result is very good and the astonishing thing is that it is audible through the whole transmission chain with all their deficits.

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