Miniaturized High-performance DAC PCM56

It is been a while I am out of making a DAC. I am enjoying what I have right now and just listening the music through my audio system.

My audio system is consisting of the 300B amplifier and DAC that sitting next to it. I was thinking that the DAC not the main unit to be shown, but the 300B is. The DAC is basically a simple and plain box that convert the digital to analog. I look at many commercially available DAC and they are all physically look the same. Many of them have only LEDs to indicate the sampling rate, inputs, and operation status. Few of them have their own LCD to show the same things like LEDs but in more fancy display. if we're honest to ourself, that display or LEDs indicator are not really important, especially when we listening to the music and enjoy it.

So, I want to try something new in this DAC project. The things that more universal and easier to use, rather than a bulky DAC box unit. This DAC project should be small enough to hide away from the main show of the system but still maintain the good sound, just like coming from the high performance DAC.

Let's get started.

This DAC project is a recycling from my previous DAC built using PCM56 here and here. It was my first fully built DAC from ground up, featuring PCM56 per channel in non-oversampling data directly from CS8412 as the SPDIF receiver. This DAC was my initial idea to make a small DAC. Today I revisiting this DAC again and will try something new on it.

This DAC is intended to powered using a battery pack. The batteries are configure in series to crated a center tap and differential voltage as requirement for the PCM56 DAC. As you may know that all vintage multibit DAC require this differential voltage. But using batteries for this purpose is troublesome. Because the recharge and the discharging rate between those series batteries need to be equal to maintain the differential voltage keep the same rating.

Then the second try using the same unit DAC but it is powered by an AC power adaptor. It is simple AC to DC converter using two diodes that create differential voltage and the other secondary output act as central tap. The problem with this configuration is the sound quality. This simple power supply is half-rectifier power supply, meaning noisy voltage and resulting to the harsh sounding of the DAC output.

We are all know that power supply is the key for a good sounding DAC.

With keep the simplicity in mind, I rework the power supply section in this PCM56 DAC. The new concept is still using power adaptor, but right now is using more universal SMPS 12-volt, 1.5 ampere minimal power supply that can be found anywhere.

SMPS power adaptor is a full-wave DC output. This is better than half-wave DC. The problem with SMPS is the high frequency noise. This is what I need to solve.

For long time, I write this blog about my audio project and I know many of the reader asking the schematic, and I always reply that the schematic is based on the datasheet.

But this post is different.

I draw the schematic for this DC-DC converter from 12-volt to differential +5 and -5 volt output as follow:

As you can see from the schematic above, this DC-DC converter is not a rocket science. This schematic is common as "virtual ground" power supply.

As you can see the first regulator is 7810 to convert and reduce the noise from DC input to clean 10-volt output. The virtual ground voltage reference output is created by using either 2 resistors (good option) or using TLE2426 (the best) option.

Next step, we need the buffer from NJM4558 op-amp before going to current boost with a pair of transistors BD139 and BD140 or equivalent.

From this schematic, we got clean, full-wave differential DC output require by the DAC.

I manage to pack all the power supply components to this tiny DAC and it works flawlessly.

This power supply section is efficient, less power from the regulator and buffer transistors transfer to heat. Using SMPS power adaptor also a good thing for the power efficiency as well.

The main goal is the sound quality which get so much better than previous stated. More analog, more relaxed sound and more fluid.

My audio system now has a small change from giant boxes from my previous DAC to this tiny DAC, but all with the good sound from PCM56 vintage multibit DAC.

I think this DAC project is a big thing for a good sounding audio system coming from a small DAC that not to be shown as the part of an audio system.

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