FIGURE Batteries Charger and switch connections

Once the shift registers have battery power, you don't need some parts.  You don't need anything that generates a negative voltage.  I had already removed the opamps, but I also removed the +/- 5VDC regs, and their output caps.  You can see the removed parts on the right of the picture below.  I also disconnected the walwart I had connected to -V in.
+V in is only used, now it supplies the 3.3V linear reg, and the 1.2V switcher.



3.3VDC upgrade
The dac comes with a 3.3V linear reg.  This is the 3 pin device with the tab, on the right of the clock chip in the picture above.  I removed it by cutting the three pins, and then heating up the tab until it came loose.

I added another lifepo4 battery, and wired it through the relay.  +3.3 from the battery/relay go to the middle pin of the regulator.  I soldered the - tab from the battery directly to a ground pad on the board, a pad that had been used by a cap I removed.




R3 and R4 are 1.5ohm, 1W resistors intended to current limit the charging current, and to provide a little isolation between the charger and the battery while the dac is on.

1.2VDC Switcher replacement

An LT1764 linear regulator generates the 1.2VDC.  This is the minimum voltage that this part can generate.  I used it because I had a few on hand.  As shown in the schematic above, pins 1 and 2, and 4 and 5 are shorted.

I put a short wire between these pins, close to the body of the part, and then cut off most of pin 2 and 4.
Pins 3 and 5 solder directly to the board, to J2-1 and J2-2.  Soldering these to pins to the board "mounts" the LT1764 to the board.
Pin 1 in bent up, and then a wire is soldered to it from the relay.  When the relay is on, 3.3V is fed to the LT1764, and it generates 1.2V to the DAC.


I tested the LT1764 stand alone first, after shorting pins 1 to 2, and 4 to 5, I connected it to 5VDC, and measured the output.  The output was high, around 1.5V.  I decided it needed an output cap, so I found a small cap (I think it's 47uf, but 10uf or larger would work), and soldered the cap from pin 3 (ground) to pin 5 (output).  Tried again, and I now have 1.2V out of the 1764.

After checking it, I installed it on the board.  With this installed, I would no longer use the 1.2V switcher, and I had already removed the 3.3V linear from the board, so I don't need to provide 12VDC to the A+ input anymore, and I removed the two wires I had connected to J1 to provide that voltage.

Powered it up, and all was good :)

Then I removed the 1.2V switcher, most of the large input caps, and the two inductors by the switcher.  The inductors are difficult to removed, I broke them with pliers (ferrite is brittle) and then removed all the pieces.

It sounded slightly better after going to the 1.2V linear, and a little better after removing the old components.  Not a huge change, I honestly expected more, but still worthwhile to do.

Amanero Power and isolated 3.3V power
Initially, I powered the Amanero and the isolated 3.3V with a simple LM317 reg and a 9V walwart.  Sounded fine, and I didn't think this power was critical since it is isolated from the dac.  I was wrong.

On advice from nige2000, I added another lifepo4 battery here, and it was a major improvement.  More so than the 1.2V regulator mod, and also I think more than the 3.3V mod.




Battery grounding
As used in this mod, each battery is like a little power supply.  So for grounding the battery, I tried to connect the battery ground as close as possible to the parts that the battery was powering.

So the ladder batteries are grounded relatively close to the shift registers.  The 3.3V battery is connected to ground by the 3.3V parts, etc.

FPGA Cap mod
There are a bunch of caps, 36 to be exact, between the FPGA and shift registers.  The caps are required because some of the shift registers are running at -3.3V,  So, without the caps, the either the fpga or the shift registers would be damaged.

I'm changing the caps to 100pf panasonic film caps.  Mouser and digikey both carry.
mouser link to caps
I bought a hundred because of the quantity discount it was just a little more than 50.  I would order some extras because they are tiny, and easy to lose a few.

To remove the existing caps, I use two soldering irons. I recently picked up a 2nd iron from hobby king, a Hakko clone that was really cheap there
hobbyking soldering iron

If you heat up each end of a cap with an iron, it just pops out really easily.

I replaced one cap, made sure the DAC still worked, then replaced 4 (first little group), and checked again.
Then I did 5 more, for a total of 9.  That is for one set of shift registers, so 1/4 of the way done, and checked again.  Checking this often slows it down, but gives me piece of mind :)

To install, I add a little dab of solder to one pad, and then tack the cap down to that pad.  Then I solder the other pad with a little more solder.  I use tweezers to hold the cap.  With this method for removal and replacement, it actually goes pretty quickly, easier than I thought it would be.

After replacing 27 of the caps, I heard a tiny bit of static in one channel.  I tried to touch up some of the pads, and the tiny bit of static became a lot of noise.  Pulled out the scope, and started looking at the shift register side of the caps.  On a few of the caps, the signal was very low, as compared to the others.  On these same caps, the signal was fine on the FPGA side.

I replaced those caps, carefully using as little heat as possible.  I checked the signals again, and they were fine.  Then I hooked it up, and static/noise was gone.

These film surface mount caps are very delicate, and you should use as little heat as possible to install them.  You should also check them after you install them.

But, I also heard an improvement in detail, realism and low end presence after making this change, so I still recommend the change, but its a borderline recommendation, because the caps are so delicate and easy to break.


exD USB to I2S card
Got a used exD USB to I2S card to try instead of the Amanero, to see how it would sound.
I had to email exD to get drivers for Windows 2012R2, but he sent me a new driver, and with that I installed it fine.

exd audio

This card needs 9V to run, it does not use USB power.  It has a few onboard regs that run off of the 9V.
There is a 5V reg, and a 3.3V reg that runs from 5V, and one around 3.1V that runs from 9V.


EDIT on March, 2018
First update in a long time lol.

Changed USB to I2S card.
Bought this one from DIYINHK
Its the

XMOS 768kHz DXD DSD512(DSD1024) high-quality USB to I2S/DSD PCB

Also wired in a Potato Semi 74G374 octal flip flop between the DIYINHK card and the DAC.


Pin 20 to 3.3V,
Pin 10 and pin 1 to ground
pin 11 to i2s master clock
pin 12 to dac data
pin 13 to xmos data
pin 14 to xmos lr clk
pin 15 to dac lr clk
pin 16 to dac bit clk
pin 17 to xmos bit clk

Pretty sure the above is correct, but I can't see the bottom silkscreen on the xmos board since it's wired up, and the xmos signal names are there.


I soldered FF into a 24 pin adapter, but its only a 20 pin device so the pin numbers are off.
The top of the adapter board, in the pic below, has pin 11 (which has a white wire in it) on the left, and pin 20 (blue wire) on the right.  So, pins 1-10 are on the bottom.





I also removed two isolators, and jumpered across to make the connections, so pic below

Decided to document my build and mods for a Soekris R2R DAC.

This page contains information on how to setup the dac.

Links
Diyaudio reference dac module thread started by Soekris
web shop to buy
dimdim blog
hifiduino blog DAC user's guide
moredamfilters blog
firmware version 0.99
moredamfilters released filters
firmware version 1.04 was the latest  download 1021full_104.skr to get everything

Go here to see how I modded this dac:
Modding the dac






Firmware and Filter updates
To update the filter, you need to connect a RS-232 port to this DAC, but these days most PC's don't have one.  And early on, people had problems establishing a connection with different 232 adapters..  It seems there are certain adapters that work.