DDDAC1794
NOS

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DDDAC1794 NOS
High Resolution Audio

Introduction

Initial
Tests

Design
Phase

Circuit:
step-by-step

Construction

Sound
Check 1

Sound
Check 2

USB
asynchronous Input

S/PDIF
Input

Foobar/Wasapi/USB
Drivers

Power
Supplies

Analog
Output Options

Testimonies

Test
Results and Specs

"Others"

A S/PDIF solution for the DDDAC1794

There was still a lot of request for good old S/PDIF, so I
designed a "S" version...

I assumed high res audio was only about PC and Mac, so I
never bothered to implement S/PDIF right in the beginning. But
I learned that there are still quite some CD Players in use or
other media players (or PCs which use S/PDIF output). As
S/PDIF is not that difficult to implement, I took this up and
started designing again. As you know the KIT is already
available for some time. I just had no time to update the Web
Site ;-)

These were the design requirements I wanted to implement in
the new mainboard:

It needed to be fully compatible with the "USB only
mainboard" and the DAC Modules, electrically and
mechanically

The S/PDIF functionality

Use best available technology (is a bit arbitrary of
course ;-)

Sampling rates Up to 192kHz (Optical 96kHz)

Option for a 12MHz XO Clock (like the ones from Guido
Tent)

Easy to switch between USB and S/PDIF source

Improve a few things on top:

LED signal part can be broken off for use at the front
panel of the chassis

Improve buffering of signals to be able to drive more
boards (so far 11 is done)

Improve timing of I2S signals with flip flop in stead
of the 1k resistor solution for data-delay

Make logic voltage 5 Volt for higher compatibility
inside the design

The only important selection was the receiver itself....
There are a few choices, like DIR9000 CS8416 and the Wolfson
WM8804. I have been listening around and for arbitrary
reasons, I thought the Wolfson WM8804 would be the best choice
for me. I bought a few chips, made some breadboard tests and
voila it woked within a few weeks. Let me explain a few things
I did in the new mainboard...

You can download the
full schematics (S/PDIF and USB mainboard version) from the
download section or push the button below:

Theory of operation of the S/PDIF mainboard

First part was the implementation of the WM8804. It is done
of course in hardware mode. In the schematic below you
recognize the option for the XO clock. Further more there is a
set of resistors, which are used to configure the WM8804 at
start up. Of course I need to Wolfson chip to output I2S
signals based on S/PDIF input signal. All easy, after studying
the somewhat complex data sheet..... In the circuit clip below
you see I have chosen to separate the power supplies for the
chip to maximize performance. In case of a Tent Clock
installed, the two ceramic Cs and Crystal should be removed
(or not installed). The 75 Ohm resistor (R1) is not on the
mainboard. It is meant to close the impedance of the coax
cable, so best position is directly at the RCA connector...

176.4 kHz Operation Note
One thing to keep in mind
please: according to design (and datasheet) the WM8804 does
not distinguish between 192 and 176.4 kHz in hardware more, So
it will not correctly lock onto 176.4 kHz unless you operate
it in software mode. So this mode will not work. Normally this
should be no issue as most spdif outputs are coming with 44.1,
48 96 or 192...

I had two problems which needed to be solved: First.... The
WM8804 is outputting 3,3 Volt logic and I wanted to control
the DAC boards (and WaveIO) with 5 Volt logic. Secondly I
wanted to be able to switch between USB (WaveIO I2S signal)
and the S/PDIF I2S signal.

After some reading and checking I came up with the
following solution. The 74VCHT244 is a bus buffer which
converts 3-5 Volt logic to 5 Volt logic. As it can go in
tri-state (high impedance on the bus) I saw a kind of two way
switch in front of me :-) Have a look at the circuit clip
below and you will understand the beauty of this solution.....

- The inputs are switched without use of mechanical
switches
- The strong output buffers can have the clock
signal drive more DAC boards (the USB only board can do max 4
DAC modules)
- All is 5 Volt logic now at the output

The final difference with the USB only mainboard is the
improved data delay. Remember? The Data needed to be delayed
half a clock cycle. I did that with a 1k Ohm resistor at the
data input. I was not sure how well this worked at multiple
boards (now 11 have been tried ;-) so as I was designing, I
simply implemented a standard flip flop to delay the data
signal with an extra half cycle. This means, that when data is
being clocked into the DAC, the state is rock solid at clock
transition...

The Board itself
Compared to the "red
USB only board, you can easily recognize the section,
where the WM8804 chip is and the extra power supplies
(3,3 volt)

At the Left is now the connection for the LED
indicators. It can be easily broken off for front panel
use, or just let it stick of course

This example shows a 4 deck version. Several 8 Decks
have been implemented without any drive issues. I know
of two cases where 11 boards were stacked with great
success !

As mentioned, the board is fully compatible with the
old DAC boards, as well the somewhat revised second
version of the DAC module, which is now being delivered.
You can freely use them through each other. So easy of
DIY is guaranteed :-)

The
DDDAC1794S
Next to S/PDIF functionality, several
practical improvements

Keep reading ...... the story continuous with installing
all software ( Programs
and Drivers )

Information

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Listening!

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