Modding the DirectStream DAC MKI

Audio Components DACs
2685

Sorry it wasn’t clear. Basically what I did was apply a large’ish bypass capacitor to the Vocm node(s) (x8) that feeds pin 2 of the AD1832. The goal being to reduce the Vocm impedance as much as possible through the audio band. I showed the 2 resistors in the divider that forms this Vocm, which is = VDD/2.

Sounds like PS Audio will also improve this node on the new DAC; it will be active buffered rather than passive bypassed.

I know Ted had commented before about this but I’m going to re-consider maybe also installing the better spec’d ADxxx parts vs the current AD8132’s. With Ted’s cautions in mind of course. Will take a look at least.

And I may also re-visit running with no transformer. The amorphous transformers in particular are quite good, but I do recall that no transformer was indeed “closer” to the music across the board basically, as one might expect. It boils down then to what is the best solution to blocking the DC on the output; my coupling cap recipe, which is quite good thankfully after a ton of effort and expense finding it, or an amorphous transformer. Only one way to really know, ultimately… I guess I’m that huckleberry :wink:

Really wish this design had a 2 pole supply… Then we wouldn’t need DC blocking caps or a transformer :confused: That would likely be the ultimate IMO. If I had the layout and could see that it was ~ easy to isolate the required areas from VSS and make it happen, I would consider doing that as well :smiley:

T

4 Likes
2686

:pray: :pray: :pray: :pray:

2687

Update- ordered the “low noise” AD8139. They do feature a much lower input noise spec through the audio band. Maybe that will bring some audible improvements vs the “low cost” AD8132?
Also planning to switch back to no transformer, at least while we wait for the amorphous w/ pure Cu. And will try a new film cap for DC blocking on the output.
I guess we shall see. Going all in here basically. T

2689

The symbol L for inductance. R for resistance and C for capacitance.

2690

It’s some passive LRC filtering in the PSU chain. That’s generally a good thing. T

2693

I’m planning to move the bridge2 board to an external box

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2694

What is the theory behind all those changes?

2696

Is your warranty still valid?

2697

I have finished improving the power supply systems of analog PCB. Previously, I added 220 uF / 25V to each C700 capacitor.
Today I soldered the same capacitor in parallel to C818. I also soldered 47uF / 25V capacitors in parallel to the C800, C809, C827. I considered removing these low-grade SMD capacitors, but kept them.

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220 uF capacitors soldered to the C700 and C800 definitely improve the SQ.
A colleague jazznut asked me to rate the sound improvement in relation to the improvement introduced by the firmware.
I believe that each of the modifications to the power system improves the sound no less than the firmware. Across the entire frequency range, the sound (instruments and voices) becomes dynamic and precise.

Why did I choose 220 uF and 47 uF? I believe that higher capacity is beneficial, and their dimensions are such that they still fit on the PCB, so I decided on this modification.

As I wrote earlier, I only use Nichicon UKZ capacitors. One of our colleagues recommends bipolar capacitors, but Nichicon’s datasheets show the advantage of UKZ. I have not tested bipolar capacitors in power systems, but our colleague, apart from his words, did not present any arguments, so I will stick to the proven UKZ.

The modernization of the power supply systems I have presented brings a great deal of sound quality, and costs only a dozen or so dollars and can be implemented in several dozen minutes.

Adrian,
yes, I encourage you to short-circuit the R705-R708 resistors. This will improve the sound, but much less than modifying the power supply. However, it is worth doing it, because we want to get the best sound.
Do not forget about the capacitors on the main + 12V power line.
Changing from 1000 uF to 2000 uF improved the sound, so to be sure I gave 4 x 1000 uF / 35 V.

I also confirm the effectiveness of the + 5V power supply modification on the digital PCB. I don’t know what capacity is optimal. I did not want to waste my time on many attempts and gave 2 x 1000 uF / 25 V. But let me give you my word, the 1000 uF capacitor significantly improved the sound, adding the second one is due to the desire to strive for the ideal.

Installing the output buffer is very laborious, but in my system it introduces a sound improvement similar to a power supply upgrade.

I encourage you to try 5-10 sheets of TDK IFL16-100NB300X200 absorber. The expense is significant, but similar to the purchase of a good fuse and many times less than the cost of any of the components of our audio equipment.

5 Likes
2698

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what should opamp use?

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I have 6 new class d single opamps that I do not use.

@tedsmith
@wiesiek
@stac
@Turbotk
@vkennedy61

2700

Doesn’t feel good to just randomly place extra caps.
Assuming that the current capacity is insufficient.

1 Like
2701

As I’ve stated before on this thread, no op-amps but those used in the DS will work without modifying the power supply to accommodate them. The op-amps need to be fully differential to be able to set the output common mode voltage (as well as many other properties.) No op-amps usually used for audio are appropriate.

6 Likes
2702

The capacitors were not placed in random places. It will sound arrogant, but I’m not theorizing, I just did something. I have spent many hours, done a lot of rehearsals and now I am enjoying the great sound of my system.

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2703

I am expecting the EDCOR transformers any day and was wondering if anyone here knows someone, or a shop, in the Boulder/Colorado area that would be able to do the soldering part of the upgrade?

2704

As a proud owner of a Directstream DAC I get an occasional opportunity to brag a little about my DAC. I especially like to point out that if someone evaluated the DAC a year or two ago, the current state of the Directstream is way beyond a one or two year old model. I enjoy pointing out the P S Audio upgrades up to Sunlight and then the upgrades we have discovered in this “Modding the Directstream DAC” stream.
My current Directstream with the transformer upgrade and the upgraded power supply, is way better than the Directstream I owned two years ago, even though it’s the same machine.
Unfortunately, I can’t tell people they could have the same great sound because the power supply upgrade is no longer available. Seems like only about three dozen of us ordered the power supply plug-in from jkrichards. I don’t know how many more people would ultimately like to take advantage of a power supply improvement, but if anybody out there (or maybe PS Audio) would resurrect the plug-in module they would get a hardy two thumbs up from me.
I saw an article a few moths ago where a large number of DACs were compared. There were a few DACs under $5.000 but most were in the $5K to $12K bracket, with a few even more expensive. The Directstream (with Sunlight), held it’s own. It finished about mid-pack. I have no doubt an easily and inexpensively modded Directstream would have finished much higher; maybe in the top quartile which would have placed it in the $8K-$10K class. It would be nice to be able to brag, if you want a great $10,000 DAC, just buy a Directstream and do the transformer upgrade, the power supply upgrade, and some of the shielding upgrades; and you’ll have your $10K DAC for less than half the cost.
Just sayin’ - ownership of a PS Audio component provides access to a community based on mutual help and improvement of the music we love. It would be a shame if some of the improvements were closed off to new people.
Oh, and a big thanks to : jkrichards, Paul, Ted, and all of the contributors to these threads.

6 Likes
2705

Blush. Thank you! We’re proud to be a part of this community of fine people.

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2706

Just wondering. Any possibility PS Audio might take over the manufacture of the power supply boards?

2707

I predict 0%.

2708

Especially where DS MkI is now out of production (I think).

2709

This board isn’t necessary to make the PSU upgrade, it’s just a convenience addition for those who often switch between internal and external supply (for whatever reason).