Introduction

I spent most of the past year working on a follow-up for the good old (10 years) DDDAC1794-PBT. I promised this would be available for DIY as well and here it is! An introduction story for the DAC and for the Dual Power Supply which is designed to go together with the DAC Board.

Why a new revision? The previous DAC model, the DDDAC1794PBT, was 10 years old. During lifetime, I received a lot of feedback from the DIY community with tweaks, ideas for use or implementation of other parts etc. Also, during that time, I gained a better understanding of PCB design, digital signal routing and analog power supply impedance and noise generation. Time to start thinking on a new version…

Another, not unimportant chain of events, was that during Covid 19, the supply chain and availability of parts was a disaster. It made keeping the DDDAC available and alive very difficult. Some critical parts went end of life as well. All those things together made me decide to make a new revision where all inputs, experience, new ideas and learnings were incorporated. I built several prototypes and did a lot of testing and listening, before I believed the final version was ready for DIY 😊

I made some detailed construction and user-manuals
Last update: 22 April 2024 (Smalle errors fixed, Disclaimer updated and few extra info’s)
Current version v1.4 (future updates: only here you can download up-to-date versions)
DAC Manual
PSU Manual

The manuals are also supplying more detailed information on how to install the board, connections, settings, bias adjustment etc etc. This will not be in the post below, to keep the post high level introduction. If you are interested in more detail, the manuals are certainly worth reading as well!

Design Goals & Features – DAC PCB

The design goals were not carved in stone and to be honest there were 3 prototype versions where I added new ideas as I went. Below is what the Final version is about (First introduction with v2.6)

• Fully based on the previous DDDAC1794 concept & design (No digital Filtering etc.)
• 4 Layer Gold Plated PCB for optimum signal routing and low impedance power / ground planes.
• Digital section with modern high-speed CMOS Logic.
• Independent MCK digital signal line (still BCK signal) with a one gate Buffer for optimum and low jitter clocking of the PCM1794 ICs.
• Design with 4x PCM1794 DACs on one single board – equivalent to old style two-decks.
• Selected capacitors for every specific function, based research and long year experience and feedback from the user community of the previous DDDAC1794 series.
• Two channels A&B with both 2 DAC ICs in parallel mode (like previous 2-deck DDDAC1794).
• Each channel can be assigned to be a Left and or Right analogue signal.
• The two channels on the board can be paralleled again for “one channel – Mono” mode (when using two mono boards you get like the old 4-deck equivalent)
• Pin-Header and UF/L inputs and outputs (for daisy chaining multiple boards).
• On-board low 1/f noise voltage regulation, separated for digital and analog section.
• Output terminals of 3.3V and 8V regulated power for external applications or tests.
• More pre-assembled, on-board SMD parts for better performance and easier DIY construction.

In regard to paralleling more than two mono assigned boards… in fact it is possible, you can daisy chain more boards and parallel the analogue outputs. If this is useful is unknown, as I did not test it sound wise.
I also recommended for the previous version to stop at 4 decks. Very few went beyond that because they just were intrigued and tried it. It does improve the sound as reported, but is it worth the extra cost? I think no, but some went for “cost no object”. After all it is a hobby….

Specifications for the DAC

Digital Input	I2S only. Inputs are 3.3V – 5V logic level compliant
Digital Input	I2S up to 384kHz / 24bits
Analog Output	~1.2Vrms single ended (two times) or ~2.4Vrms balanced (FS0dB)
Output impedance	~68 Ohm in Stereo Mode and ~34 Ohm in Mono mode.
Digital Power Input	4.0 Volt (~10-50mA)
Analog Power Input	9.0 Volt (~ 200mA)
Digital Power output	Regulated 3.3 Volt (recommended < 150mA)
Analog Power output	Regulated 8.0 Volt (recommended < 100mA)

Board Layout and Dimensions

Board size	130mm x 180mm
Mounting holes spacing	120mm x 170mm / Dia. 3.5mm

The DAC PCB and Kit for DIY (through hole parts) 

If you would decide to build this DAC, this is what you will find in the full DAC kit:

• PCB with all SMD-Parts already assembled.
• Plastic bag with all the through hole parts and other assembly material.
• For the actual kit the correspondent part list – the part list may differ in future versions, depending on availability of certain parts.

Just check the Audio Creative Web-Shop

Design Goals & Features – Dual Power Supply

Also these design goals were not carved in stone. Two prototype versions were built. Below is what the Final version is about (First introduction with v2.5)

• Based on the previous DDDAC1794 PSU design.
• Audiophile electronic MOSFET rectifying with the famous LT4320.
• Selected capacitors for specific functions, based on research and long year experience and feedback from the user community of the previous DDDAC1794 series.
• Two separate PSU-Units on a single board, which can be physically separated for single board use thanks to easy to use break off points.
• Two output terminals with variable voltage setting (roughly between 3 and of 15V regulated power).
• Two terminals for connecting an optional choke to change filtering from RCRC to RCLC.
• More pre-assembled, on-board SMD parts for higher performance and easier DIY construction.

Specifications for the PSU per unit

AC Input	7Vac – 15Vac (for DDDAC1794MK3 recommended use: 2x12Vac)
DC Output	Adjustable 3Vdc – 15Vdc
Maximum Current	1A – take care with power dissipation! Bigger heatsinks needed
Choke Option	Recommend 1H with max 4Ohm for DDDAC1794MK3 use

Board Layout and Dimensions  

Board size	130mm x 130mm
Mounting hole spacing	120mm x 120mm / Dia. 3.5mm

           

The PSU PCB and Kit for DIY (through hole parts) 

If you decide to build this, this is what you will find in the full kit:

• PCB with all SMD-Parts already assembled.
• Two heatsinks. (Size is intended for use with two DDDAC1704 MK3 boards.)
• Plastic bag with all the through hole parts and other assembly material.
• For the actual kit the corresponding part list – (the part list may differ in futures versions, depending on availability of certain parts.

Just check the Audio Creative Web-Shop

Mains-Transformer Suggestions

There are two options: two independent transformers with single secondary winding or one transformer with two separated secondary windings.
Do NOT use windings with center tap!! This will not work properly.
In my own setup, I am using a 50VA transformer with two 12Vac separated secondary windings.
I suggest a minimum 50VA Transformer for optimum compromise between headroom and
cost. Bigger is “better” but also more expensive. Try for yourself if it is really “better”.

Even if a 15VA transformer will work fine, I would not use those small ones, as they are more prone to large output voltage deviations under different (no) load conditions.
The AC voltage of the transformer should stay under 15 Vac for proper operation.

Measurements

I know, some might say “I only measure with my ears!” Yes, fine, I do that as well, but that is more like “reviewing & evaluating”. I always measure everything I design, in depth. I need to be 100% sure, the electrical specifications and behavior of the design is beyond doubt! I also want to understand if my design choices have lead to the expected results. Only then, when I am satisfied, I can lay back and start listening.

So let’s first check the measurement results for the PSU.

Let’s have a look at the most important results for the DAC:

The dominating distortion d2 in single ended is only 0,1% – no one will be able to hear this. Your speakers will produce much more and most music is well below 0dB Full Scale signal level anyway.

For the balanced output things are better of course as d2 is mostly cancelled out. Only d3 stays dominant at, again, only 0,03%.

From a DAC you expect a straight line in terms of frequency response. Without a coupling capacitor or OPT, that is the case of course. See the graph below. The balanced output is, no surprise, 6dB (double) more than the single ended output. Values are absolute in dBV (in real Volt you get: ~1,2V and ~2,4V)

Honestly, for a NOS DAC with passive I/V, these results are remarkably good. Better than the previous ones. These are solid results, supporting the listening results, which were also exceeding my expectations.

OK, I am indeed satisfied now. Enough technology and background, how does it sound?

Test Setup for the listening-review

The listening review had three goals. First, to listen in general and compare with the “old” DAC. Secondly, I tried two versions. One with Nichicon UKA and one with RR7 Polymer capacitors in the analog section. Number three to check if the choke was still making such a significant difference.

I strongly believe you need to be able to switch back and forward, while listening, between different alternatives, to be really able to come to conclusions. Real A-B comparison so to speak. Going blind is even better – when possible.

This was my Test Setup:

• 50VA Transformer with 2x 12V sec.
• DDDAC Dual Power Supply
• Both sides having the DDDAC AE Choke option connected
• Two DAC boards in stereo mode. One with the UKA capacitors and one with RR7 Polymer versions
• DDDAC specified Sowter Output Transformers (OPT) from AE Electric – Link to Website –

The inputs from the two Sowter Output Transformers are switched between the balanced (POS & NEG) outputs of the two DAC boards. Each board is running in stereo mode.

Listening

General impressions versus the “old” DDDAC

This is not a 100% one on one comparison, as the setups are not 100% the same, but they are comparable enough.

I have been listening to all kinds of music, Classic, Pop, “High-End” stuff etc. At the end the outcome was always consistent. Sometimes less, sometime more obvious.

Spoiler, the differences are not world shocking. Nevertheless, I could hear the fruits of all the efforts to implement all described above. There is increased ease of listening. That extra touch of naturalism. Small details & texture have improved. SSSs are softer and natural. Focus is sharp. I must admit, part of this is also thanks to the choke option. My reference DAC has also CLC filtering. The cooperation between all elements in the MK3 system, is just very harmonic.

Specific impressions on two different capacitor options in the analog section

To recap, (nice pun), the only differences between the two boards I listened to, were the 16 capacitors in the analog section. I was just very curious on the effect with different capacitors. I used:

1. Nichicon UKA series (Audio grade: Selected materials to create superior acoustic sound)
2. Nichicon RR7 series (Ultra low ESR and Impedance, even at high frequencies)

The outcome was pretty clear. The UKA capacitors sound (as far as my ears are concerned…) dynamic, detailed and offer a very spatial soundstage. Bass is punchy and voices are pinpoint. More in the back of the sound stage than forward like with the RR7.

The RR7 capacitors offer a more forward sound, larger voices and instruments. Total sound is more laid back and kind of warm. Bass is more prone, rounder and thicker, soundstage is still open and clear.

As I will be asked anyway: My personal preference is to use the Nichicon UKA. This is the reason they are also in the kit.

Now, IF (!) your personal preference, or the simple need to adapt to rest of the audio system, would want you to rather have the polymers (kind of “Englisch” sound”) installed in your DAC, just send me an E-Mail. I still have some and could send you a set. I will charge you just the cost of parts and shipment… Offer lasts as long as I have some sets left.

Again, chokes

Conclusions

• Design goals were all met, which is nice 🙂
• The sound print of the MK3 is the same as the old DAC, very analogue, very open and detailed.
• Do not expect “unbelievable”, “my jaw dropped”, “I could not listen to the old one anymore” kind of differences. The old one was not that bad, LOL – I categorize this as “worthy improvement” absolutely worth all the effort.
• The MOSFET rectifying paid off.
• Again, in the final versions, the use of the Choke was clearly an eye opener. In fact it is a “must-tweak”
• The DAC & PSU are, also thanks to the easier setup (more SMD), very nice and rewarding DIY-Projects!

In summary, it has been great fun to put the whole project “DDDAC” upside down and inside out. I very much like the results and honestly, I would not know what to do next to further improve. For this, experience showed, that feedback from the DIY community, from people who actually built the DAC, has always lead to new ideas and improvements.

Ergo, start building, tweaking, experimenting and enjoy the music. Because that is still what this was all about.

If you are interested after all this reading and you want to build this DAC, Audio Creative is the exclusive global dealer for the DAC and PSU kits. Just check their Web-Shop If you will.

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