Revised DAC Module Board with Tentlabs Shunt regulator
for analog section and FET current source for the "Pin 20" bias
Finally ready.... Two important sound quality improvements, based on broad experience of the DIY community, are now implemented in the new DAC board module:
The embedded Tent shunt is for the 8Volt only. The 3,3V stays LF33, with option to mount a shunt replacement (for those who really want to do this.
My tests showed that the 8V does the most improvement and honestly I could not hear true difference on the 3,3Volt...
- Embedded, under licence a Tentlabs Shunt regular, on the DAC board for the analog supply voltage (8Volt)
- Embedded a FET constant current source for "PIN 20". Nice improvement of sound quality. On top a clever way to easily adjust the bias
And of course totally back wards compatible with mainboards and old dacs (you could even use them mixed if you want)
Now some technical stuff:
As you can see the trimmers to adjust the FET CC to 0,4mA (resulting in 2,75 Volt DC bias at the output of the DAC
are at the edge of the board. So even when stacked you can trim every DAC chip to get 0,4mA. If all are set right, the DC Bias will result "automatically" in 2,7 to 2,8 Volt DC.
The value itself is NOT critical. so don't overdo it to get lets say 2,750000 Volt ;-)
The trick is simple. Just added a 100 Ohm resistor. now you can measure at the test point for 40mV. If you do this at all points things are fine even for multiple boards.
I have tested this of course and the 40mV is in the middle of the trimmer, allowing for spread in other FET batches.
It is also very stable. after 24 hours I had a 1mV difference which is NO problem at all. The DAC works fine even plus minus 10%
Just to mention, both 6k resistor AND the current source can be installed. So you can experiment and try yourself
For technical documentation, circuit diagram and PCB layout, just go to download section of this website
or click directly here:
"Documents for the Powered by Tent Version"
Introduction, how it all started
In the past year I have been working on a
huge project: designing a DAC which will play 192kHz / 24bit material from a PC (or Mac...)
There are many DACs who can do this, but I wanted to make sure to design a NOS version,
as so far, every listening test proved, that this actually leads to a more open, natural and detailed sound.
I found this to be possible by using the well known PCM1794 and avoiding the digital filtering.
This proved to be VERY tricky, but I managed to find the tricks to do it.
It has been a great adventure with much to learn and a fantastic result in the end....
I hope you enjoy reading my page as much as I enjoyed developing this DAC!
How did this one get started in the first place?
Excellent Question! It all started with several listening sessions we did with Reinhard , Klaus and Bernd to further tweak
the DDDAC1543 MK2. We did several tests with power supplies and even building 20 Tower Module versions (which by the way still
showed improvement over 5 towers and 10 towers... which led to new understanding on why parallel DACs are sounding better.
(See "Others" for this).
|Another superb Audio Session:|
The very nice GOTO Horn equipment from Klaus (and Reinhard and Bernd as well) are revealing an unparalleled rich detailed and dynamic music reproduction.
For testing of new designs, just the best you can get:-)
But now, how to play HD Music?
But now we ran into an interesting problem.
Reinhard brought quite some HD music files with him (up to 192kHz / 24bit) and of course wanted to play these. But that does not work just like that.
The point is, that you just cannot play this HD material on a TDA1543 based DAC and also the PCM2707 based USB interface (a synchronous USB chip)
is not allowing anything above 48kHz..... So I had this sudden URGE to start thinking what to do next ..........
|Parallel DAC testing:|
Here you can see, how we are creating a 240 chip TDA1543 DAC by hooking up the DACs from me (60 chips), Klaus (60 chips) and Reinhard (120 chips)
Is paralleling so many DACs the way to go?
Again the right Question! Even though we all agreed, it was stunning that so many chips in parallel still improved the whole sound experience,
we also agreed, that this is quite a BIG thing to do... Just the power consumption is awesome. 12 Volt with 14A.... And still no HD Music? Challenge accepted!
We needed a new DAC design which plays HD up to 192kHz / 24 bit AND sound as good as the DDDAC1543 MK2 on 44.1 / 16 material
|Another view on the DDDAC1543mk2 240 chip version:|
This was just great fun, even when the whole thing looks against everything you should do in high end audio (look at the wiring and wide space between boards)
it was amazing that we still had improvement
These points were considered:
- We need an USB asynchronous receiver
- The right Audio player (Foobar, WASAPI)
- Windows 7 PC (for true bit perfect streaming)
- A DAC Chip, with current output (to enable paralleling outputs and passive I/V)
- A DAC Chip allowing NOS (Non Oversampling mode, or avoid digital filtering)
- Clean power supplies are a must
- After ample thinking only one choice stayed in my mind..... the PCM1794....
Keep reading ...... the story continuous with initial testing ( Initial Tests )