PCM1794 mother-/daughter board concept

I want to begin with saying that this is not my original idea. I was heavily inspired by other, very competent, designers out there.

The idea is to have a Main/motherboard with ASRC/SRC, PSU including a vigortronix smps AC to DC supply. The DAC boards, configured in dual with one PCM1794A/channel, is then mounted on top of the motherboard. I have 4pcs new PCM1794A, so I can try using one DAC board or two (total of 4x PCM1794).

The main-/motherboard is 100*150mm dual side with 70u copper.

I have sent the first version off to a board house, the motherboard that is. The DAC board I’m still doing some small adjustments on. But that will need to be a four layer board (100*50mm) to get a decent layout. Making the DAC boards as expensive to have made as the main-/motherboard.

The rendering is not very good, I apologize about that.

There are 3x 0.03ohm Ferrite beads connecting the digital GND to GND, and an X2 capacitor between GND and safety earth. The voltage regulators are LT1963’s.

Between them and the actual supplies is one 22uH 1A Epcos inductor in 1812 size.

DAC boards.

Current layout:

The Pinheaders are not going to be as in the rendering. I will use pinheaders on the main-/motherboard and stackable female headers on the DAC boards.


The mainboards have been sent from the board house.

Files to get the DAC boards have been sent to the board house this morning. Not as in the rendering I posted earlier but with some changes, including 4 outputs/channel (L+/- & R+/-).



Collected the boards from the post office today. The mainboards that is, the DAC boards are still in production at the board house.



I started to populate the first mainboard today.

Again, I am sorry about the bad quality pics. My daughter was sleeping and I did not want risking to wake her by going in that room to get the Nikon D5200 DSLR.

As, maybe, can be seen in the pics I have one bridge (pin1&2 of the SRC4192) to clean up after the hot air reflow.



Though I have been in alot of pain the last couple of days, I did manage to populate a few more spots on the first DAC mainboard.

I’ve also ordered most of the missing parts from Mouser.



The Mouser order is on it’s way, I noticed…too late…that I had accidentally ordered the SCR4190 for the second board, not the SCR4192. I don’t, yet, know what difference there is between the two. I do have an AD1896A at home as well and to my knowledge, they are all pin-compatible. That is: SCR4190, SCR4192 and AD1896A, is to my knowledge interchangable without too much effort.



Got the PCM1794 expansion boards.

4 layer boards and again I got twice the number of boards expected from elecrow



Started to stuff the first of the DAC boards.

I haven’t cleaned off the flux in this pic. The flux paste used here is Amtech (genuine), very good but very hard to clean off the PCB.



 Etched a board for balanced to SE as the I/V and buffer/filter boards has differential output.

The I/V and buffer/filter board uses 2x OPA1642 and 2x OPA627/each, the diff to SE board use 2x OPA627.

The design use a mix of SMD’s and TH parts, and a C-L-C filter on the PS.



I will most likely go non-src/asrc, meaning I will use only the four layer dual PCM1794 NOS board/boards. So non-OS PCM1794 in mono mode using two per channel.

Since I got ten of the boards from elecrow, I sent one board as a gift to my good friend Dave in Minnesota USA. It’s nice having a good friend like that, we send eachother parts and boards as gifts and discuss DIY and other things via email.

/Mayday 2017/10/07

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