PCM2706 to PCM1794 help needed

[Mayday]

As part of my modular DAC build I've got two PCM1974 boards with I2S inputs.

I recieved a PCM2706 USB to I2S board a while ago.

Now to get these to play nice together...

With two boards set to mono differential mode via a pair of Edcor XSM 600:600 I got a week music signal through alot of noise.

I removed the Edcor trafos to make sure they weren't causing it. I then used only one PCM1794 board set to 24-bit I2S and stereo.

Now I get only noise.

Then there's the connection between the boards....

PCM2706 has
GND
MCK
LRCK
BCK
DATA

While PCM1794 inputs are
SCK
BCK
LRCK
DATA
GND

When I got the faint audio I had it connected the same way as now.
I connected MCK out to SCK in. Before the flaming begins, remember I'm new to this stuff.

I know that TDA1541A can run of just GND, WS, DATA and BCK.

Would it be able to run PCM2706 to PCM1794 via?
GND
BCK
LRCK
DATA

Leaving SCK in on the PCM1794 boards and MCK out on the PCM2706 board not connected?

 

[Redshift187]

You can't leave SCK disconnected.

GND -> GND
MCK -> SCK
LRCK -> LRCK
BCK -> BCK
DATA -> DATA

Should work. Have you tried different sampling frequencies?

 

[Redshift187]

What are your configuration inputs on the PCM1794 set to?

 

[Mayday]

I've tried all I2S formats.
I'll try again with the other board (I initially tried with two boards in mono differential when I got some sound behind the noise) and see if that works.

I've only scratched the surface of the settings for Foobar2000 so might have made a mistake there.

 

[Mayday]

Tested one of the PCM1794 boards with the PCM2706 today with CHSL - 0, Mono - 0, FMT1 - 0, FMT0 -0.
So stereo I2S.

No sound at all.

I'll try with other opamps, if no go, then with the other board, then if still no go..other board with other opamps. After that I don't know. If there's still issues, they are probably me being to dumb to set foobar2000 correctly for the setup.

 

[Redshift187]

Is there a schematic of the PCM1794 boards?

 

[Mayday]

Is there a schematic of the PCM1794 boards?

Yes, but I don't know if it is ok with the forum rules to post it since it's not my design.

 

[Redshift187]

If the schematic is publicly available it's okay.

 

[Mayday]

Well I found it easily enough.
I have the stereo board (two of them), but found a schematic from the same designer for a dual board as well.
I had to take screenshoots of the schematic as it's a PDF.

I desoldered the 680R and replaced them with 330R as per the dual schem.
I also put 22pF on the single opamps according to the dual PCM1794 schem.

 

[Redshift187]

What is that component connecting the two ground planes to the right of the PCM1794?

If it's anything but a 0 ohm jumper, it needs to be replaced with a short.

 

[Mayday]

What is that component connecting the two ground planes to the right of the PCM1794?

If it's anything but a 0 ohm jumper, it needs to be replaced with a short.

It's a ferrite bead.
I can't find the values for them now, but IIRC it was lower than 0.5R.
Should I replace that with a jumper?

 

[Redshift187]

A ferrite bead should be okay, but you can try replacing it with a jumper. I know from experience that if you try to isolate the two ground planes you end up with a whole lot of noise and not much else.

 

[Mayday]

I've replaced the ferrite beads with jumpers, and I removed the 22pf caps I added. The boards are back to standard apart from the 680R being swapped for 330R.

Hopefully I'll have time to test the setup again tomorrow.

 

[Mayday]

Didn't really feel up to much DIY today, but I did try a single PCM1794 fed I2S from TekDevice WM8804 board.

Same thing, audio, but under a thick layer of noise. I have replaced the ferrite beads with jumpers and removed the 22pF caps I had added.

Used my sqeezebox classic as the spdif source.

 

[Redshift187]

Maybe it's the WM8804 board.

Have you tried something other than Foobar?

 

[Mayday]

Maybe it's the WM8804 board.

Have you tried something other than Foobar?

I used my sqeezebox Classic as source when trying with the WM8804 board.
It gave the same result as the PCM2706 board. Faint audio covered by noise.

Though it has been a long time since I used the SB so I need to read up on how to control output formats.

 

[Mayday]

Well I tried with the other pcm1794 board today.
SPDIF via WM8804 board.

Silence, not even noise.
I tested with all jumpers set to 0 on the the PCM1794 board (I²S).
WM8804 board jumpered: sdout: 1 gpo0: 0.
Again, I²S (24bit).
Is a NOS PCM1794 capable of 24bit I²S?
Don't have the datasheet in front of me, I'm writing from my phone.

Do I need a digital filter/OS between reciever and DAC?

I've seen schematics online using this very combination, WM8804 & PCM1794.

 

[Redshift187]

I have one DAC using the PCM1794 in stereo with 24-bit I2S in and one in mono with the filter disabled. But with the filter disabled it has to be 24-bit right justified (aka standard).

 

[Redshift187]

I think it's time to start measuring voltages. What are the voltages at the IC of pin 1 (MONO), pin 2 (CHSL), pin 11 (FMT0), pin 12 (FMT1) when the settings are all 0?

 

[Redshift187]

Actually, looking at the boards they look okay. I'm starting to suspect a fake PCM1794.