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

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WalterW

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Joined 2012
Paid Member
carlsor said:
danielutzu brought up the subject of using a Pass DC coupled B1 JFET buffer just as I was thinking of using them as a buffer between the balanced outputs and the Cinemag transformer. This would provide a >1megohm load to the DAC while providing a stronger signal to the transformer. I suspect that 4 and 8 stack DACs sound better by providing a much lower output impedance than a single DAC board. Shouldn't the buffer accomplish the same thing while eliminating the interaction between the DAC outputs and an inductive load?

I once put B1DC buffers after LDR volume controls with incredible sounding results.
Click to expand...

Try it, and keep us informed :D I'm a big Pass fan.
 
K

KevinTams

Member
Joined 2004
danielutzu said:
I'm strongly thinking about buying a DDDAC. Rather than connect it directly to the amplifier (a F6 I just built), would you guys recommend I use a JFET DC-coupled buffer like the Pass B1 / Mezmerize? The main advantage would be that I can then use a stepped attenuator for volume control on the analog side, and it eliminates the need for output caps. One day, this will be a fully balanced system; does this change anything?
Click to expand...

If the buffer is dc coupled how would it eliminate the need for an output cap?

I take the output from the balanced outs because there is minimal dc offset, no caps, no Tx. I don't have any problems with ground loops, maybe I've been lucky.
If you build a single dac DDDAC the you will probably need a buffer. I use a passive pre into a Pass Aleph30 with my 4 stack DDDAC and it works fine. Actually it's bloody brilliant!!

BTW the DDDAC is a very easy build.
 
M

merlinx76

Member
Joined 2004
I want to use this DAC on my PC but I am unsure if it can do all I need from it. Can anybody tell me if I can have an audio input coming in through my sound card and have it go out through the USB to the DAC?

I asked Doede but he had never tried and said he wouldn't be able to try for a few weeks.
 
dddac

dddac

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Joined 2003
blog.dddac.com
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Nounours18200 said:
Hi,

I am in the final step of my DDDAC-1794 building, and I am looking for the cabling diagram of the Sowter transformers (and the Mundorf caps).

I have searched on the Doede site but I have not found how to connect the Sowter: they have 5 wires, Grey, Pink, Orange and Brown, White, but I do not know how to conect them to the Mainboard outputs.

Thanks !
Click to expand...

red and white are the primary... red is hot
pink and brown are secondary. pink is hot
do not use grey....
 
M

merlinx76

Member
Joined 2004
ArthurDK said:
Why would you do that ?
Click to expand...

Because my wife's computer needs to be connected to the sound system too.

ArthurDK said:
Why would you do that ? You will have do make a AD conversion on the audio in, which probably would not be very high quality, and then convert it back in the WaweIO.
Click to expand...

The sound quality of this connection is not as critical since I would use my computer as the source when I want optimal sound quality. The input in question is already digital anyway (optical SPDIF) from my wife's computer.

ArthurDK said:
Why not use one input in the preamp for the DAC and one for the other audio source ?
Arthur.
Click to expand...

Both computers need to be connected to the sound system at the same time. My computer is used for a lot more than just music.
 
N

Nounours18200

Member
Joined 2004
threshold-lovers.com
Nounours,
Which Sowter are you using? If are the ones from Doede (1298x) you should see 6 wire and the schematic connection is behind the packing note
Enrico
Click to expand...


red and white are the primary... red is hot
pink and brown are secondary. pink is hot
do not use grey....
Click to expand...

Thanks ! just to be sure, regarding the primaries: I have to connect them to the "Pos" and "Common" pin outputs of the Mainboard ? (I mean that the "Neg" pin output is not used )
 
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D

danielutzu

Member
Joined 2009
Salas made the DCB1 buffer which is direct-coupled, thus avoiding any caps in the signal path. Is this what you used? So I would use the balanced outputs from the DDDAC into a balanced DCB1, and from there on into a balanced amplifier.

carlsor said:
danielutzu brought up the subject of using a Pass DC coupled B1 JFET buffer just as I was thinking of using them as a buffer between the balanced outputs and the Cinemag transformer. This would provide a >1megohm load to the DAC while providing a stronger signal to the transformer. I suspect that 4 and 8 stack DACs sound better by providing a much lower output impedance than a single DAC board. Shouldn't the buffer accomplish the same thing while eliminating the interaction between the DAC outputs and an inductive load?

I once put B1DC buffers after LDR volume controls with incredible sounding results.
Click to expand...
 
C

carlsor

Member
Joined 2008
danielutzu

My LDR volume control used a DC coupled B1 buffer without any caps. I put a 50ohm pot at the negative end of the bottom 2SK170 JFET with a slightly higher Idss than the upper 2SK170 to adjust the output near 0.0mv offset. This can be used in a balanced pair to help adjust the balanced output offset near 0mv. The balanced outputs from the DDDAC PCM1794 are at 2.7VDC above ground. This should work for a balanced input that is allowed to float above the amplifier ground.

I plan to use Belleson 225ma voltage regulators: +12VDC for the top of the buffer and - 6.25VDC for the bottom of the buffer. These cost $36USD ea. The buffer center would be near enough to 2.7VDC. 2SK170 JFETs are reported to sound best at 9VDC which I used with breathtaking results.
 
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N

Nounours18200

Member
Joined 2004
threshold-lovers.com
I start the final assembly phase of my DDDAC.

I absolutely need a SPDIF input in addition to the USB input, so I have to use the "1543-Mk II SPDIF & I2S receiver" card to feed the Mainboard and to have the choice between the USB input (WaveIO card) and the RCA SPDIF input.

The Dac has 3 separated Power Supplies in an external chassis (3 independant power supply cards from the DDDAC 1794 shop), delivering :
  • +12V for the 1794 Mainboard : this is the Card A
  • +12V for the 1543 MkII SPDIF/I2S board : this is the Card B
  • and +5V for the WaveIO board: this is the Card C.

so the external Power Supplies Cabinet has a 6 pins cable to be linked to the main DDDAC 1794 chassis:
  • 2 pins for the GND and+12V of the card A,
  • 2 pins for the GND and +12V of the card B,
  • and 2 pins for the GND and +5V of the card C.

I have drawned the following general cabling diagram to explain my question:

An externally hosted image should be here but it was not working when we last tested it.


The WaveIO card I2S output should be linked to the 1543 card (I2S input).

My question is HOW should I connect the "V+" pin at the output of the WaveIO card ? It has to receive +5V, but can connect it to the +5V of the main WaveIO card (as on the attached diagram), or should I get this +5V from somewhere else ? (maybe the 1543 VB+ output ?)

I am not sure at all of my cabling, so I prefer to ask prior doing anything wrong ...

Thanks !
 
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