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Upgraded Single Board PCM1794 NOS DDDAC
Upgraded Single Board PCM1794 NOS DDDAC
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Old 24th November 2014, 08:34 PM   #11
WalterW is offline WalterW  Netherlands
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Join Date: Oct 2012
Location: Utrecht
Upgraded Single Board PCM1794 NOS DDDAC
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Pass F5, F5Tv3, ACA, Aleph J, DDDAC1794, DCB1, BA3-preamp, VFET CSX1, Pass F6, Pass M2-HPA, VFET-X balanced, Pass J2
'If you see me talking to myself, don't worry. I'm getting expert advice'
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Old 25th November 2014, 02:58 PM   #12
Undarra is offline Undarra  United Kingdom
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Subscribed too. Thanks for all the effort Carlsor.
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Old 25th November 2014, 06:05 PM   #13
Supersurfer is offline Supersurfer  Netherlands
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Quote:
Originally Posted by stijn001 View Post
Thanks, subscribed.

I'd be interested in a little board which will allow for the one SOT-23 package + resistor/potmeter. Any suggestions anyone?
I am thinking of using the resistor and transistor in smd package, it will not be difficult soldering these to the legs of a bourns multiturns pot. This will keep the footprint small for easy mounting at the resistor position on the dac board.

Regards,
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Old 27th November 2014, 03:45 AM   #14
carlsor is offline carlsor  United States
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Location: Saint Augustine, FL
Default 1/2 Clock Delay Circuit

This upgrade takes most of an afternoon to build and install, but is well worth it.

These are my initial sq impressions from this change: I hear MORE music!
- Cymbals sound 100% right for the first time.
- Voices are more articulate
- Sound is more crisp and vibrant. No smoothing here.
- Same amount of detail, but it sounds more coherent and "right"
- I got drawn into musical nuances of familiar CDs that I never noticed before.
- More focused placement of instruments in the soundstage. I could almost hear the size and shape of instruments.

The board is about $10 usd of parts, but I also bought a 5V Belleson SPM78 regulator ($36 usd) to comply with the Blue Main Board voltage. Yes, a 5V regulator makes the DAC with this upgrade sound more accurate and smooth compared with my original 3.3V Belleson. According to the data sheets the 74VHCxxxx chips switch state many times more quickly when operating at 5.0 volts. Adaptor boards can be bought on eBay but could take a month to receive. 3pcs SMD Converter Adapter PCB SOIC14 LGA14 to DIP14 | eBay

The I2S resistors should all be 100 ohms the 1000 ohm resistor for DATA must be replaced with 100 ohms! The bottom of the main board had to be modified by cutting BCK foil traces and adding jumper wires. See pictures below. You can see the delayed signal wire from the 2-Chip Board going through one of the clock foil trace holes to the five 74VHC164 chips.

I initially built and installed a 1/2 clock delay circuit above the main board. Later I built a second 1/2 clock delay circuit board but installed it on the bottom of the red main board which puts it out of sight. I think some of the wires lengths may be a little shorter, but this location is no less time consuming to implement. I used 24ga CAT 5e solid wires. For multiple connections I loop a single wire through the points as much as possible.

For the bottom installation I drilled an M3 hole through the adaptor board pair and main board with a plastic nut spacer and screw to hold it firmly in place.

The Belleson and some other Vregs need more load than from the seven 74VHCxxxx chips to provide optimum regulation and sound their best. The connection to the WaveIO isolator provides enough extra load, but if you are using an rpi or reclocker with its own isolator you may need to add a 330 ohm resistor across the Vreg load.

My engineering mind cannot figure out why new components, circuits, PS, etc in the digital domain of 1's and 0's have to go through a burnin period, but my ears tell me this is necessary.

Below is the 74VHCxxxx chips circuit diagram pulled from page 3 of the DDDAC 1794S NOS manual that should be used as a guide for wiring and installing this circuit board. Also included is a BOM and installation pictures.
Attached Images
File Type: jpg dddac1794 delay half-cycle.jpg (483.8 KB, 1830 views)
File Type: jpg 2_Chip Back.JPG (346.6 KB, 1745 views)
File Type: jpg 2_Chip Installed.JPG (551.5 KB, 1700 views)
File Type: jpg Main Bot Mod.JPG (289.3 KB, 1403 views)
File Type: jpg Bot half clock delay board.jpg (352.1 KB, 1373 views)
File Type: jpg top half.jpg (291.0 KB, 524 views)
File Type: jpg BOM half clock delay.jpg (254.1 KB, 483 views)
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Old 27th November 2014, 08:07 AM   #15
stijn001 is offline stijn001  Netherlands
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Quote:
Originally Posted by Supersurfer View Post
...
I'm also thinking to first build the CCS’s and calibrate them, then replace the pots with fix resistors, to reduce the tempco difference the pots are prone to. I think the tempco behavior is crusial when they are stuffed in between a dac stack.

I’ve ordered some 2SK246Y from Ebay. That way I can just work with a bit of perfboard if I have to.

My workbench still needs setting up. Work on my kitchen is taking priority at the moment..
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Old 27th November 2014, 09:17 AM   #16
zdr is offline zdr  Belgium
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I still don't understand all the hype about non oversampling dacs. I could clearly hear artifacts on simple signals all over the place.
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Old 27th November 2014, 01:01 PM   #17
stijn001 is offline stijn001  Netherlands
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Nice little adapter for the 2SK208.

20 Pieces 0 95mm to 2 54mm SOT23 to SIP3 Adapter SMD Convert Double Sides | eBay
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Old 27th November 2014, 06:44 PM   #18
nige2000 is offline nige2000  Ireland
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Quote:
Originally Posted by stijn001 View Post
thnx
looks useful
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Old 2nd December 2014, 07:00 PM   #19
pz1 is offline pz1  Netherlands
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Default 1/2 delay clock for red motherboard dddac 1794

Carlsor advises to insert 1/2 delay for the red motherboards for better SQ.

I am wondering if someone has created or will create a PCB for this, having a Group Buy. I am interested to order, but have not the knowledge myself to produce.
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Old 2nd December 2014, 10:35 PM   #20
rickmcinnis is offline rickmcinnis  United States
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Quote:
Originally Posted by pz1 View Post
Carlsor advises to insert 1/2 delay for the red motherboards for better SQ.

I am wondering if someone has created or will create a PCB for this, having a Group Buy. I am interested to order, but have not the knowledge myself to produce.
Doede offers such a thing - get the "blue" board. I did not want to do the mod so that is what I did!
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