Modding the DirectStream DAC MKI

[Turbotk]

Lovely work Yuriy.

You are a highly skilled audiophile. Now- I have an assignment for you to try sir, now that you’re rockin’ the 8139. I think you’ll be amazed. It’s an ~ easy thing to rework really (with a heat gun) and for now at least (to hear it) no stock values or parts need to be changed. Can be completed in an hour.

Simply take the stock OA Rfb (R3, R4) and move them to connect diagonal across C8, C9. That’s it. Per the image below. You may find it easier to stand the R on its side to do this. Basically the R3, R4 no longer connect to the top pads; instead they now connect to the top of C8, C9. Call this the “OA topology mod v1”.

You’ll just have to trust me for now. And hey, otherwise, it’s a piece of cake to put back.

Be careful with the heat gun to blow generally away and outward from the PPS C8 and C9. IME the stock soldering takes a ton of heat to get loose; one of the hardest things about all this, at least until the leaded solder goes in… Try removing the stock discrete reg pass transistor for example (sheesh, that’ll fight ya…)

On the DAC2 I raised the stock regulator Vout to 10.5v; this allows more gain in the OA circuit and thus more output level. It was not hard really, a few reg parts needed changing. BUT the tougher part was, to get 10.5Vout also required a higher Vfeed into the reg; had to tap that elsewhere. But you don’t need to do any of this for now.

DW has DAC2 and it’s playing very, very well. It continues to put down the comers. Lately that is his (repaired) TDA1541 tube DAC (the Abbas), also this week the darling of the month Anti-Mode X4 processor (TK note- too easy

Meanwhile here I am using DAC1 and it sounds superb. DAC1 has a new 2 pole double throw-down PSU for the OA section and runs +/- 5.4v to them; this allows to simply ground Vocm and NO blocking device on the output (trafo nor caps) (that’s relatively big, at this level).

Both DACs uses a precision discrete LPF on the output with Morre treated pure Cu air core inductors. That works quite well IME. Call this the “OA as bit buffer + passive LPF” approach.

Next I’d like to get back onto the “OA as LPF” approach, but am out of DAC boards to do it with for now. The other 2 sound so good currently I don’t want to change them. We’re also onto chasing the last ounces of performance from the preamp currently so the focus is there currently. Most people simply don’t realize how much their preamp cr@ps on the sound. Sure can hear it with DAC1/2 though!

T

[scotte1]

HDMI and USB “shorting plugs” update:

Well folks I have about 90 minutes of casual listening with the plugs deployed and I gotta say (sorry to say), I am not noticing anything materially special so far – nothing obvious across multiple recordings, ripped and rendered via JRiver Media Center via the DS Sr. DAC/Bridge II combo.

I have an inkling/notion of some things but I need some more time with the widgets, with a broader swath of recordings and some CDs/SACDs spun up via I2S and the PSA DMP disc spinner.

Nothing unpleasant to note either, mind you.

More to come…

[Vmax]

I think possibly your limiting problem is the USB and i2S lower noise floor is overcome by the Bridge II noise. You cannot get quieter than the noisest unit inside the box.

[scotte1]

Maybe…but not ready to concede to that possibility at this juncture.

Cheers.

[brian.fitterman]

I totally agree with VMaxx. I used to use the bridge. Did not like it. Not even close to stand alone streamer.

[vkennedy61]

@scotte1 - If you haven’t, it’s definitely worth the effort to test with and without the BII in the MKI. If you don’t have one, perhaps you can borrow a streamer (endpoint) for a test. You might be very surprised. Even a lowly Sonore microRendu would do. I currently don’t have a spare (gasp) or I’d loan you one.

[lufubu]

it shouldn’t be difficult to get the bridge out of the box

[vkennedy61]

Sure, but without the BII, he’ll need some sort of endpoint for his digital stream. Innous, Sonore, Lumin, etc…

[lufubu]

will work out of the box, not without

[jkrichards]

When I was testing the Bridge II in my system nothing sounded that good with it installed even on other inputs. I felt it was contaminating all the inputs and could tell instantly when I pulled it out. I have 2 DS units that I can run simultaneously and do an A/B comparison on the fly by selecting AUX 1 or AUX 2 on my preamp. I would move the plugs from one to the other and one could clearly hear which unit had them installed. I did the same test between the DS and my Terminator II 12th. The one that had the plugs in it sounded better.

[jazznut]

JK, with all the mods and tests you’ve done, was there anything that in your perception especially opened up and freshened up the top end?

[dchang05]

I only use USB plug because both I2S are in use. The improvement was realized when I removed it from the back, and there was something missing. It is not like a MK2, but it does help a little bit. Thanks, JK!

[jkrichards]

I feel the VOCM mod and ether the Jensen or the LL 1948 made the biggest difference.

[scotte1]

Addendum:

[@Vmax @vkennedy61 @jkrichards ]

BTW, I have a SHAKTI STONE AIR placed on top of the DAC along the rear edge, running parallel with the length of Bridge II Ethernet card and “covering” the AC inlet as well.

Might be a factor…

[jazznut]

Thanks, nice, so I should experience this potential as soon as the mods are done. While everything, especially in terms of air and palpability was and will be improved by all those noise eliminating improvements firmware updates and mods so far brought, the top end still is the most important area to improve since long imo.

[yuriy]

Thanks Turbotk.
Well, sir, I followed your advice and tried this mod. I don’t have a hair dryer, but it’s quite possible to get by with two soldering irons)) Before starting, I had to think about how best to solder the resistors R3, R4 to C8, C9 so that later, if necessary, they could be unsoldered and not damage the capacitors. To do this, I decided to put the resistors at an angle so that its lower edge touches the upper edge of the capacitor and then it can be soldered from the capacitor, touching only the resistor. You can see it in the photo.
And so, the first inclusion, I fix the volume drop by approximately -6dB. This is not a problem and is compensated by its rise in the preliminary. Sound. You can immediately hear the extended middle and enlarged images, which I like. But the scene is flatter, lost depth and 3D. A serious decline in the low frequencies, starting with the midbass. HF also have a decline, but less than LF. At the same time, the sound became simpler and coarsened, the timbres were depleted. Dynamics and drive have fallen, it seems that there has been a phase shift between the mids and lows.
An hour later, I decided to return everything back, the original strategy was justified, the capacitors were not damaged (last photo).
Perhaps in my case this mod gives such a result, someone will have it differently. Anyway Turbotk, thank you very much for this idea and suggestion of its implementation, it was exciting!

[jkrichards]

Today we did some test with the Audio Precision analyzer on both my modded DS with Jensen’s and my Terminator II 12th.

DS:

Terminator:

[jkrichards]

Everyone here liked the DS sound as it sounds more real. Not so perfect.

[Vmax]

Which graphs are the DS and which the Termiinator DAC?

[Turbotk]

Interesting, so sorry it did not work out for you. My experience was different. But that was awhile back already. T