Personally I probably would not bother swapping OA unless I also had a more transparent transformer in place. Just my opinion.
I used these from Mouser:
584-AD8139ARDZ-R AD8139ARDZ-REEL
High Performance Low
MAR 25, 2022
10 8.550 85.50
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Like to ask, as in the case where we are using external 12vdc linear psu to power the analog PCB, would there be any good benefits in doing the 5vdc that enters the digital input PCB ?
Does the 5vdc support only the USB input or everything else ?
Ask this because I only use the AES/EBU
There are three 5V supplies. The bridge and the display use one or two of them. The digital board uses one. USB is on the digital board so the 5V for the digital board supplies the USB power (as well as the FPGA, etc.) AES/EBU is passive (basically termination resistors, cap isolation and a wire to the FPGA.)
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Ok, so I feel like the rendering, the d/a conversion is really good here. And we switched to the pure Cu amorphous transformers yesterday. It sounds amazing.
But weāre trying to lift some blanket off the sound, relative to the other DAC, which has the lowest noise floor I know of (by far). Its immediately audible, a sensation even.
Thinkingā¦ seems it has to be either the transformers or the output nets or both, bringing the relative blanket. So tonight we went to this step: āā¦Weāll have to cut the OA output loose from the common output net to do so. This will also allow us to use wire of choice from OA to transformer.ā
So, cut the OA loose from the output net. Direct wired in new connections from OA output to transformer, and transformer to XLR conns. I used Audience Moore treated OCC stranded 21ga; maybe the quietest, most natural and transparent wire I have. Chosen based on experience with Audience AU24SX RCA cables.
Its playing very nicely now, but I feel we still need to get some blanket off, relatively speaking. Weāll keep at it as time permits.
We may give the transformers a rest and try the TK_Caps recipe again too. I do recall that did sound wonderful early on. Closer to the music, more connected overall so maybe that meant less blanket. Of course then I had not yet heard the other DAC. But that might help answer the question about transformers.
Aside from that possibility, next step will likely be to try the āphilosophicalā change to a 2nd OA pair using the OA as pure bistream buffer, feeding digital into a very high quality parts 2-stage passive LPF for d/a conversion. Should be interesting 
T
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Are you leaving the capacitors like this?
Or use some kit to avoid solder stress.
I donāt understand, can you explain?
Sorry.
I mean attaching components to prevent them from loosening or applying too much force to the soldering tip.
See white dots.
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Unfortunately, my possibilities are limited by what I have read in the forum and the skill of my technician. the capacitors are so small and light we thought it wouldnāt be a problem.
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Please let me know the results in SQ
Like ask what value and manufacturer?
I have the xs4400, dedicated 12V supply and have now made the Vcom mod as suggested by T. It has made another substantial improvement in clarity and soundstage depth. I also finally put the modded unit on my bench for some measurements. While the DS is never going to win anyway awards for its analog performance its considerably better than stock. Mostly due, I think, from the better transformer which saturates less at the low end than the stock. The multi-tone test looks good above approx 1K.
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The Directstream DAC won plenty of rewards for its analog performance when it was released. What other DAC has ever had as many rave reviews from all those that do that.
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Do users go back to Snowmass to run the Vcom mod? Iām getting a bit excited.
When I say analog performance I mean measured (THD, THD+N, SNR, effective bits etc). The analog output stage is limited by the stock transformer and other passives. It does measure better with the new transformer and is pretty good above 1K. At lower frequencies and higher amplitudes the magnetics still ultimately limit performance. It has always sounded good, now it sounds really good. I love what T is exploring as ultimately it may be possible to achieve both excellent sound and good measured performance.
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What is the VCom mod? I just had the transformers and JKRICHARDS board with power supply added. I also got purple fuses everywhere. I donāt think Iām up to sending my dac back across the country for more mods but I am curious what the VCom mod is.
Like myself, youāll have to read about it above. It will take me time to understand it completely (even what to order) but it involves at least changing caps and possibly resistors on the DSD board.
DG thatās great work, thanks for sharing. What tool do you have for these measurements? Can you share more about your findings please?
I have an AP system 1 but have never used it (and an old Win95 PC to run it) (from a retired engineering friend). I should use it or get rid of it 
And yes, after some time to ponder Iām pretty excited about the upcoming next deep dive trial; OA and filtering change approach. Thinking, hoping this may be the key to dropping the noise floor in comparison to the other DAC. If it succeeds, think weāre there basically 
Meanwhile the rendering Iāve been hearing since OA change rd 1 has been pretty stellar 
So we keep goingā¦
And then thereās the output caps recipe too, also waiting their turn.
Turbo
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Hi T,
I use an RTX6001 to as a measurement instrument with various software. Issue with DS has always been high distortion and elevated noise floor when compared to SOTA DACs. Paul has never prioritized that. If you look at the original Stereophile review or the stuff on SuperBest Audio dudes you will see that.
Cheersā¦ Doug
Gentlemen,
capacitors soldered to C6, C7 have little effectiveness, the overall power supply of operational amplifiers should be improved, and this is achieved by capacitors soldered to C703 (large capacitors on the left and right)
Another significant improvement in sound is provided by the modification of the Crystek clock power supply - this is done by a capacitor at the Q800 transistor.
One more little note,
bipolar capacitors are not recommended for polarized systems (power supplies). One must take into account the rapid aging due to the degeneration of one of the electrodes due to the lack of refreshment of the formation of aluminum oxide - an insulator on one cladding.