8 × AK5578EN + 8 × AK4499EQ ADC/DAC Boards

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ishizeno

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Joined 2015
Power Regulators

The evaluation board is using 4 × NJM78M05 power regulators. To make things even better, we will use the LDOVR LT3045-78XX 5V instead, as an optional upgrade. They will be mounted on the same board as their related AD817A/AD operational amplifiers (used for the Jung-Didden regulators), either on a PSU board, or directly on the DAC board (still trying to figure out that one).
 
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ishizeno

Member
Joined 2015
DAC and XMOS PCB Layers

The AK4499EQ evaluation boards (base board and DAC board) are both using a 4-layer design. Therefore, we will go for that much simpler design as well, because it should be good enough for a first version, and it will allow us to mimic the reference design much more easily, while reducing manufacturing costs and lead times. There is so much that I have to learn for this project that I want to keep things as simple as possible wherever I can...
 
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ishizeno

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Joined 2015
DAC Board Capacitors

Here is the list of big and medium capacitors on the DAC board:

220μ big capacitors:
C6, C14, C35, C90 (VREFH/VREFL)

220μ medium capacitors:
C3, C11, C29_1, C89 (VDLL)
C_X3, C_X4, C_X5, C_X6 (VDD/VSS)

10μ medium capacitors (MLCC SMT, Hybrid Polymer Aluminum, or Vishay Polymer Tantalum):
C22, C23, C86, C93 (VREFH)
C49, C50, C87, C94 (VREFL)
C18, C25, C26, C28, C82, C83, C84, C85 (VOP)

Knowing that space is our primary constraint there, I would love to get recommendations for the 220μ capacitors (both big and medium ones).
 
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ishizeno

Member
Joined 2015
Isolated XMOS Board

I am now starting to work on the XMOS board, and I am thinking of getting it isolated like the excellent OSVA. What I mean by that is that the XMOS chip would be on one side of the board, while the digital outputs and oscillators would be on the other side, each within their own isolated sections. The two sides of the board would be connected together by a set of Si866x low power digital isolators. This image shows how different sections of the PCB are nicely isolated from each other through all the layers of the PCB.
 
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Markw4

Member
Joined 2016
ishizeno said:
...shows that the only large components that need to be mounted on the North and South sides are four large capacitors.
Click to expand...

A picture of the eval board at: https://www.diyaudio.com/forums/digital-line-level/314935-es9038q2m-board-457.html#post5830912
if you open the picture, then click on the white X in the lower left corner it will blow up to full size, or you can right click to download at full res.
Under the daughter board are some more electrolytic caps. There are also a few components on the bottom side of the motherboard.

The rows of yellow and green banana plugs along the long sides of the motherboard are alternate power entry points for the adjacent circuitry. That circuitry provides the analog power for dac chip outputs. There are also a few components of that circuitry on the bottom of the board.

The I/V opamps on the daughterboard are powered directly off the incoming +-15v rails, and as such are not quite ideally powered.
 
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M

Markw4

Member
Joined 2016
ishizeno said:
...we should be able to make a small 80mm cube with a Sitara SoC and two AK4499EQ DACs for $300...
Click to expand...

Only if you will be satisfied with rather compromised sound quality.

Sabre dacs are not easy to get right either. Allo, in India, is expected to come out with a good ES9038Q2M USB dac soon. Probably better sound quality using those, or some you get them to make for you rather than doing a poor version of an AK4499 design.
 
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ishizeno

Member
Joined 2015
Markw4 said:
A picture of the eval board at: https://www.diyaudio.com/forums/digital-line-level/314935-es9038q2m-board-457.html#post5830912
if you open the picture, then click on the white X in the lower left corner it will blow up to full size, or you can right click to download at full res.
Under the daughter board are some more electrolytic caps. There are also a few components on the bottom side of the motherboard.

The rows of yellow and green banana plugs along the long sides of the motherboard are alternate power entry points for the adjacent circuitry. That circuitry provides the analog power for dac chip outputs. There are also a few components of that circuitry on the bottom of the board.

The I/V opamps on the daughterboard are powered directly off the incoming +-15v rails, and as such are not quite ideally powered.
Click to expand...

Thanks a ton for the link. This picture will be a lot more useful than the low-res version on the AKM website.
 
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ishizeno

Member
Joined 2015
Markw4 said:
Only if you will be satisfied with rather compromised sound quality.

Sabre dacs are not easy to get right either. Allo, in India, is expected to come out with a good ES9038Q2M USB dac soon. Probably better sound quality using those, or some you get them to make for you rather than doing a poor version of an AK4499 design.
Click to expand...

Of course! But I would not learn anywhere as much by getting someone else do the work for me... I'll work as long as necessary to make it good. And the BoM will be closer to $400, but we'll make sure to make the Sitara SoM optional. Without it, the cube will just be exposed through the XMOS directly.
 
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ishizeno

Member
Joined 2015
Markw4 said:
The Reference Voltage power should be very, very clean, no noise contamination, and low impedance. ESS recommends putting their equivalent power, AVCC, as close to the dac chip pins as possible for best results. With specified noise and distortion at -120dB or lower, you are getting into an area that requires careful design.
Click to expand...

I'll try to fit it all on the DAC board then. That will make for an interesting challenge...
 
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ishizeno

Member
Joined 2015
Additional Capacitors

Here are the other capacitors that we need to mount on the DAC board:

C352, C357, C358, C361 (+15V MVDD): 470μ
C350, C351 (+15V MVDD): 470μ
C300, C306, C320, C326 (+15V MVREF): 470μ
C302, C308, C322, C328 (+15V MVREF): 100μ
C304, C310, C324, C330 (+5V REG): 100μ
C305, C311, C325, C331 (+5V REG): 100μ

The BoM for the DAC brick is being compiled on this sheet.
 
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sciencesky

Member
Joined 2013
chris719 said:
I don't know what kind of filtering you've tried on the PoE input, but a common-mode choke is a good idea. There are also some nice 3-terminal "feedthrough" caps that Murata makes we have used to good effect. Could also look into using LDOs with better rejection up to 1 MHz, which seems to be around where the best IC regulators top out.
Click to expand...

There is no filtering only capacitors. The PoE part belongs to the board of our client and its the first time that we actually have one of their boards on our desk after nearly 2 years.
There is also an isolated DC-DC-Converter Module after the PoE part but that thing does nothing except voltage conversion and heat production :D

You really need to be careful with those ready to go regulator modules!
Input and output filtering is a must!
 
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chris719

Member
Joined 2004
sciencesky said:
There is no filtering only capacitors. The PoE part belongs to the board of our client and its the first time that we actually have one of their boards on our desk after nearly 2 years.
There is also an isolated DC-DC-Converter Module after the PoE part but that thing does nothing except voltage conversion and heat production :D

You really need to be careful with those ready to go regulator modules!
Input and output filtering is a must!
Click to expand...

Yes, most of the modules suck. The exceptions being the SIP / IC package types from Linear, TI, and Intel/Enpirion.
 
C

chris719

Member
Joined 2004
Markw4 said:
Only if you will be satisfied with rather compromised sound quality.

Sabre dacs are not easy to get right either. Allo, in India, is expected to come out with a good ES9038Q2M USB dac soon. Probably better sound quality using those, or some you get them to make for you rather than doing a poor version of an AK4499 design.
Click to expand...

What part of his post is making you think it will be compromised? Just curious. Small size and proximity to the SoC?
 
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ishizeno

Member
Joined 2015
chris719 said:
What part of his post is making you think it will be compromised? Just curious. Small size and proximity to the SoC?
Click to expand...

I do not want to speak for Mark, but I suspect that my original BoM estimate was way off ($200 to $300) and created some confusion. Without Sitara SoM (about $100 when buying 1K), the BoM is already at about $420, and I am far from being done. I expect it to reach anywhere between $500 to $600 when everything is said and done. It's certainly not cheap, but I'm not cutting any corners, at least within the space/volume constraints that I have to deal with. And if these constraints prove to be insurmountable, I'll got to a 2 OTO units footprint (160mm × 80mm).

Also, the likelihood that a complete newbie like me could pull this one off must seem very low, but appearances can be deceiving ;-)
 
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