A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

Jump to Latest
#5,981
mbrennwa said:
Really? The DDDAC docs show the 5 V PSU connected to GND.

Also, all metal parts that are accessible from the outside should be connected to safety earth, and that probably includes the USB plug for the digital input -- or am I wrong?
Click to expand...

I see what you mean, the 5 Volt Ground is shown as a ground sign. You could think all of those are connected together, which is not the case. Maybe I should make a footnote there. Due to the Isolator on the USB Board, you have two "grounds" or commons, the one at the dac side (the WaveIO is supplied with 5 Volt and ´ground from the mainboard) and the ground from the PC and the 5 Volt power supply.

The metal part should be at safety earth through the USB Cable and the PC power connector...
 
#5,982
dddac said:
I see what you mean, the 5 Volt Ground is shown as a ground sign. You could think all of those are connected together, which is not the case. Maybe I should make a footnote there. Due to the Isolator on the USB Board, you have two "grounds" or commons, the one at the dac side (the WaveIO is supplied with 5 Volt and ´ground from the mainboard) and the ground from the PC and the 5 Volt power supply.
Click to expand...

Ahaaa!! A complete drawing showing the full grounding scheme would be useful (avoiding the use of the same symbol for different "grounds"). Maybe it would be best to entirely avoid the word "ground" (or "GND"), because it can mean so many different things. For example, "safety earth", "analog common", "digital zero", etc. are much more specific, which greatly helps to avoid such confusion.

dddac said:
The metal part should be at safety earth through the USB Cable and the PC power connector...
Click to expand...

...if the DDDAC USB is connected to a computer, and if the computer is connected to safety earth (think of a laptop running on battery or a class-II device without a safety-earth connection). Isn't that too many "ifs" for safety?
 
#5,983
dddac said:
As the pictures do not show a complete wired situation, I like to ask you to make a schematic drawing and post a picture of it.
Click to expand...
Here the schematic of my wires in particular the earth and the safery ground
 

Attachments

  • Alim DAC.png
    Alim DAC.png
    24.4 KB · Views: 412
#5,986
doc007 said:
Effectively I did not include the 2 flat cables to the motherboard and the LEDs on the front panel.:scratch::scratch:
Pierre
Click to expand...

I believe the connection between the USB board and the DDDAC mainboard has a "GND" connection (I guess that's "digital zero"), which is probably connected to the NEG output of the 5V PSU. I am writing this out of memory, so you better check if this is correct.

You wrote in an earlier post that you connected the NEG output of the 5V PSU to chassis / safety earth (I believe). This connection is not shown in your drawing. Did you change that in your build?

Also, pin 3 of the XLR outputs are connected to chassis / safety earth via the rings of the RCA connectors, which are connected to the chassis. So pin 3 and pin 1 of the XLRs are connected to each other, which seems wrong to me. I have never tried to combine balanced (XLR) and unbalanced (RCA) outputs in the same unit, so I don't really know what's the best way to do this. Do you really need both?

Regarding your problem with the fuse blowing, I don't really know what's going on. I still suspect some kind of (hidden) wiring error.
Did you measure the resistances of the POS and NEG outputs of your 12V and 5V power supplies to chassis/safety-earth (as suggested earlier)?
Does the fuse also blow if you remove the connections of the PSUs to the DDDAC and the WaveIO board?
 
#5,987
dddac said:
The metal part should be at safety earth through the USB Cable and the PC power connector...
Click to expand...

mbrennwa said:
...if the DDDAC USB is connected to a computer, and if the computer is connected to safety earth (think of a laptop running on battery or a class-II device without a safety-earth connection). Isn't that too many "ifs" for safety?
Click to expand...

I just checked the USB connector of a commercial, CE-approved DAC with USB input (not the DDDAC). The chassis is properly connected to safety earth, but there is indeed no connection to the metal part of the USB connector. I don't know for sure, but it seems it might indeed be okay to have the USB input floating the chassis/safety-earth... mea culpa!
 
#5,993
billyboyk said:
I have read, again, the full Doede's article, I think that I will reinstall things how they have to be at the beginning, forget the separation between digital and analgo, between left and right and come back to original design, just supplied by 2 LL1694, and use the LL1638 in my tube amp.

I waste too much time to debug the situation instead of appreciate the music...
Click to expand...

Hey billyboyk, did you make it work? If so, I'd be interested to read how you solved the issue.
 
#5,995
doc007 said:
I only use the RCA outputs and not the XLR. I await the response of Doede.
Click to expand...

I have been really thinking about your sketch and I tried a few things my self in my hobby room and I was not able to reproduce any problem. The sketch you posted is in fact ok. it should work. That is the technical side of things. What I do my self (for reasons) is to put the safety ground wire (green/yellow) from the power line to the chassis, the transformer screen and pin 1 from the XLR and using cables with the screen connected to pin 1 at ONLY the source side. The hot and cold, pin 2 and 3 are coming from the Output of the sowter transformer. The cinch outputs are floating versus the chassis, so the shielding comes from the signal (or chassis) ground from the receiving amplifier.

Ergo no clue why the fuse blows... but feel free to ignore it and let the 5V unit float with the USB Board

and.... even when you do not use XLR, it would make sense to at least wire them correctly, won't you agree?
 
#5,997
:cubehead:
dddac said:
I have been really thinking about your sketch and I tried a few things my self in my hobby room and I was not able to reproduce any problem. The sketch you posted is in fact ok. it should work. That is the technical side of things. What I do my self (for reasons) is to put the safety ground wire (green/yellow) from the power line to the chassis, the transformer screen and pin 1 from the XLR and using cables with the screen connected to pin 1 at ONLY the source side. The hot and cold, pin 2 and 3 are coming from the Output of the sowter transformer. The cinch outputs are floating versus the chassis, so the shielding comes from the signal (or chassis) ground from the receiving amplifier.

Ergo no clue why the fuse blows... but feel free to ignore it and let the 5V unit float with the USB Board

and.... even when you do not use XLR, it would make sense to at least wire them correctly, won't you agree?
Click to expand...
Thanks for your answer
I will rectify my connections and keep you informed
My schema will be the following
 

Attachments

  • Alim DAC.png
    Alim DAC.png
    28.4 KB · Views: 422
You must log in or register to reply here.
Top Bottom