DDDAC 1794 Build

This article is about building my own version of the DDDAC 1794 NOS DIY dac. Designed by Doede Douma. The NOS stands for Non Over Sampling DAC, without any filtering.

More info:

There is a massive thread diyaudio about the DDDAC 1794; nos-192-24-dac-pcm1794-waveio-usb-input. It can be a little overwhelming; it contains today almost 8000 messages. In 2017 it were only 6000 messages to read.

Audio Creative has published some nice article about this DAC. They are also the official channel to for available DIY DDDAC 1794 kits.

You can start a DDDAC 1794 NOS build very basic and depending on your budget and time extend it in time. I started my build in 2017 and completed most at the beginning of 2018.

In its most basic form it contains:

  • Power supply (kit available, but of course you can use your own)
  • Mainboard (sold as kit)
  • One or more DAC boards (sold as kit)
  • Output decoupling choice (default a cheap capacitor is supplied)
  • An enclosure and even that is an option.

In the most basic form only a SPDIF input is available. Other sources can be connected to an I2S input.

Specs of this build:

  • DDDAC 1794 subsystem exist out of:
    • 1x Blue Mainboard.
    • 2x DAC with Tent boards.
    • 2x Cinemag 600/600CLI Transformers as output decoupler.
  • Raspberry Pi 3B
    • HifiBerry Digi+ Pro as I2S source for the DAC.
    • An Allo Isolator for galvanic isolation between the buildin Pi and HifiBerry + DAC.
    • Moode Audio as software distribution.

Special features of this build:

  • Nice enclosure with:
    • OLED Display with information about the current track
    • Source button to choose from:
      • Raspberry (long press of the source button pause or continue current track)
      • Digital Source 1 SPDIF/Toslink
      • Digital Source 2 SPDIF
    • Soft power down for Raspberry
  • Allo Isolator mod to use both Crystals from the Hifiberry
    • Allo Isolator doesn’t required 6.5VDC
  • Software mods for:

All schematic, drawings, tweaks etc can be found at my github repo dddac1794build.

Article Content:

  • Overview
  • Main board + DAC modules
  • Power Supply
  • Output decoupler
  • Raspberry Pi
  • Enclosure
  • Source selection
  • OLED Display
  • Soft power down
  • Part list

System Overview

Overview is provided by three diagrams:

  • Blocks
  • Actual used electronics and global interconnections
  • Electrical scheme (kiKad)

The functional blocks of the system are:

This system DDDAC 1794 building blocks

The used electronics and connections are shown in the following diagram:

Connections between the blocks

The exact connection between the modules are shown in the diagram below:

Schematic of the system

The remainder of the article provide more detail of some of the modules.

Main board + DAC modules

The DIY kits supplied by Audio Creative are beautiful kits. You directly see that PCB are high quality. SMD components are already mounted on the PCB, you only need to solder the through hole components your self.

It includes silver wire for connecting the DAC with the main board. The kit also include Dale resistors for the I/V conversion. If you like to use silver solder, you can buy also a small amount from Audio Creative. You can find the construction documentation and more also on the DDDAC page of Audio Creative.

DDDAC1794 main and DAC module kits
Assembled main module
Assembled DAC module
Main with a single DAC module

Currently my system contains 2 DAC modules and have room left for a third DAC module.

Power supply

For the Mainboard and DAC boards a stock DDDAC 12V PS kit is used.

DDDAC1794 12V PS

The other components use 5V, but no DDDAC 5V PS kit is used for it. The 5V PS exists out of a clean 5V and a dirty 5V. The clean is used by the Hifiberry and the Allo Isolator (at least the clean part of the isolator). The dirty 5V by the Pi and other auxilary components. The 5V uses a toroidal transformer with secondary 2x6VAC, 30W. Followed by a dual DIYIHNK 4.17uV 5V/1A regulator. It uses a TPS7A4700 for regulation.

Dual DIYIHNK 4.17uV 5V/1A regulator

The Raspberry Pi is direct fed by the 5V dirty on the GPIO connector 5V, the USB PS connector is not used.

To the Hifiberry a connector on position P3 is added. This is used to fed the clean 5V to the Hifiberry and the Allo Isolator. If you had used the PS connector of the Allo Isolator it self, that voltage had to be 6.5VDC, because the voltage drop of the onboard 5V regulator.

By the way both the Raspberry, HifiBerry and the Allo Isolator all have onboard 3.3V regulators that are used to fed the electronics onboard.

In my build there is no connection between the dirty and clean ground. Make sure that in that case you also have the mod for the clock select.

Output decoupler

I replaced the default no name caps first by 2x MKT-Capacitor ax. 2,2µF ERD 1813 NOS. Later followed by Cinemag 15/15b transformers.

And finally settled with two Cinemag CLMI 600/600C to decouple the outputs. Both are nicely mounted to the side of the enclosure with a 3D printed mounted (Thanks Henk!).

Cinemag transformer mount

Raspberry Pi

Hardware

The Raspberry Pi is in this system not only important as a I2S source for the DAC, but the Raspberry Pi also controls most of the auxiliary modules like the display and source selection.

You can see this back in use of the Raspberry expansion header:

Raspberry Pi GPIO usages

The hardware is stacked as following:

  • On the bottom the Raspberry Pi
  • Followed by a PiFace GPIO Shim
  • Then the Allo Isolator
  • And finally the HifiBerry Digi+ Pro

The PiFace GPIO Shim makes it possible to breakout the GPIO and others pins, while continue stacking other boards.

PiFace GPIO Shim -Header Breakout

Special attention is needed for letting the Allo Isolator and HifiBerry work together and still honor the separation between the dirty and clean 5V modules. See an other article for more details.

All GPIO interfacing including the power supply for the Pi connected to the PiFAC GPIO Shim.

Operating System

Tested a lot of software distributions. Started with Rune Audio and currently Moode Audio 6.4.2 is used. It provides an easy to install system, a nice (web) GUI and is easy to mod.

It requires two configuration settings for make it work for this specific system:

First select the the HifiBerry Digi+ Pro as I2S device, which will require a reboot.

Second force to use 24 bit as output signal, source that aren’t 24 bit are converted. You can also provide a fixed upsample rate. See the article Selective Resample for an other interesting option.

Additional software for the display, source and soft power are handled in the previous paragraphs.

Enclosure

The chosen enclosure is a model of the Hifi2000 Galaxy line, the Galaxy Maggiorato GX388 330 x 280mm x 2HE 10mm front panel SILVER, including a Base Galaxy GX.

Galaxy Maggiorato

The base plate makes it easy to mount all components first on the base plate and then place the base plate in the case.

Base Galaxy GX

To see if everything fits the following floorplan is used.

floorplan

For designing the front and pack panel I used Front Panel Designer from Schaeffer. Within this application you can directly see the cost of the design and place an order with Schaeffer. Also it provides nice renders of the panels.

The project files can be download from:

I wanted the display a little bit sunken in the front, but not the full 10 mm. Therefore also on the back some material should be extruded to bring the display more to the front.

front panel
back panel with deepened location for the display PCB

I am very satisfied with the end result:

Source selection

The system has three sources:

  • Raspberry Pi, I2S
  • Digital 1, SPDIF or Toslink
  • Digital 2, SPDIF

Selecting the source is done with momentary switch next to the display. The switch is directly connected to the Raspberry Pi.

On power on default Digital 1 is selected. When the Raspberry is booted the Raspberry is default selected as source and the switch led is turned on. As long as the Raspberry is booting the screen will stay dark.

A short press will select the next source. If the Raspberry is selected a long press will pause or continue the current track.

The led current is to much for the Raspberry it self, the soft power down PCB contains a transistor to drive the led.

A dual relay module is used for selecting between I2S or SPDIF and selecting between Digital 1 or 2.

Dual Relay Module

The relay module is also controlled by same daemon on the Raspberry Pi as for controlling the display. The module is mounted against the back panel of the enclosure.

OLED Display

The system contains a small display to show source information.

The display specs:

  • Size :1.3″
  • Type: OLED
  • Resolution: 128×64
  • Interface: I2C
  • Driver: SSD1106

The display shows information about the Raspberry or the Digital Source (1 or 2):

If the Raspberry Pi is active the following information is show:

For controlling the display a daemon is running on the Pi. This daemon is written in Python and will work uses two libraries for the main functionality:

  • pyhton-mpd2 is used to connect to MPD for reading out information about the current song and playlist.
  • python-luma.oled is used to drive the display itself.

The daemon also contains the functionality to read the source button and control the led in the source button. Due using the MPD client library, you don’t have to integrate with Moode Audio itself. It will work on any MPD based or compatible audio player, even over the network if you want a separated display.

Soft power down

There is risk to corrupt the SD card of Raspberry Pi when it isn’t proper shutdown and I do power down my audio equipment when not in use, a solution is needed.

A software power down module is developed for this purpose. See the article Raspberry Soft Power Down for more information.

Part List

To give a clue about the number of parts and investment required hereby the list of my specific system.

Small parts like wiring, additional nut, bolts and some connectors are not on the list.

nrdescriptionsubsystemSuppliercountpricetotal
1DDDAC 1794 blue mainboarddacAudiocreative1€ 165,00€ 165,00
2DDDAC 1794 DAC boarddacAudiocreative2€ 159,00€ 318,00
3DDDAC 12V PSdacAudiocreative1€ 94,00€ 94,00
5DIYINHK Ultra Low Noise PSstreamerDiyinhk1€ 41,82€ 41,82
6Block RDK 30VA/2x6VstreamerConrad1€ 19,64€ 19,64
7Raspberry 3streamerSOSsolutions1€ 36,95€ 36,95
8SD Card 8 GBstreamerSOSsolutions1€ 7,95€ 7,95
9Hifiberry Digi+ ProstreamerSOSsolutions1€ 42,95€ 42,95
10AC Main C14 Chassis partcaseConrad1€ 5,25€ 5,25
11Fuse 20mmcaseConrad1€ 1,20€ 1,20
12Torx147 Optical SPDIF Receiver 192kcaseDiyinhk1€ 3,35€ 3,35
13CinchConnector Rean AV NYS367-9caseConrad1€ 4,36€ 4,36
14CinchConnector Rean AV NYS367-2caseConrad1€ 4,36€ 4,36
15CinchConnector Rean AV NYS367-4caseConrad3€ 4,36€ 13,08
16Cinch-connector internalcaseConrad1€ 1,48€ 1,48
17OLED Display 1.3″ I2CcaseDiymall by ebay1€ 8,51€ 8,51
18Galaxy Maggiorato GX388 330 x 280mm x 2HE 10mm front panel SILVERcaseModus1€ 53,00€ 53,00
19Base Galaxy GX345/348/385/388caseModus1€ 8,00€ 8,00
20Case feetscaseModus4€ 3,50€ 14,00
21Frontplate JobcaseSchaeffer1€ 58,89€ 58,89
22Backplate JobscaseSchaeffer1€ 42,38€ 42,38
23Relais board arduino 1x relais (active high)caseDX1€ 2,30€ 2,30
24Relais board arduino 2x relais (active low)caseDX1€ 4,00€ 4,00
25Attiny85case?1€ 2,30€ 2,30
26Switch TRU COMPONENTS LAS1-AGQ-22E, BLcaseConrad2€ 19,82€ 39,64
27Allo IsolatorstreamerSOSsolutions1€ 60,95€ 60,95
28Cinemags CMLI-600/600 setdacAudiocreative*1€ 249,00€ 249,00
29PiFace GPIO ShimstreamerKiwi Electronics1€ 5,95€ 5,95

The partlist can be downloaded at:

2 Replies to “DDDAC 1794 Build”

  1. Fantastisch werk! Ziet er prachtig uit! Deze build zal als referentie zijn voor mijn projecten. Ik moet nog behuizingen maken voor twee dddacs.

    Groet,

    Robin

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