Modding the DirectStream DAC MKI

I use 47 and I think that’s also what JK recommended at the end, I think he just initially used higher values. I wouldn’t worry what he heard or not as long as you hear it :wink:.

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Thanks for the reply re your DAC – interesting!
APS still says on their website that they use 220uF.
(I’d link but something tells me that might trigger an allergy around here…)

Oh and I’m not worried, I just like to understand what’s really happening as much as I can.

I didn’t notice anything like JK was banned or left in anger…seems I was on holiday or so :wink:

Here’s my way to do a Vocm mod.

I shouldn’t use word “proper,” because my way is as intuitive as the other ways people chosen. I’m just theorized, but I like the result.

You do realise that there’s no audio signal on the Vocm line, right? All we need is a stable reference.

He uses these because they are cheap and easy to install. This works, but it’s a compromise.


Ted said:
“this is one place that adding capacitance of almost any type won’t harm the board so using a big cap there isn’t inherently bad, it just might not be as good as one might expect.”
Which I personally took, as not good enough. Which resulted in my “sandwich” solution.

I think, it’s because his power supply switching board works but, again, a compromise. It equalizes good and mediocre power supplies (most likely, making good PSU sound worse). Because:

  1. long 12V cord
  2. a lot of contacts (connectors) in the way
  3. no capacitors

Yes it’s a reference point. The quality of power affects it. But the capacitors are here to clean the noise as much as possible IN PARTICULAR REGION, which is not the sound frequencies, but starting from sound frequencies.

We’re trying to minimize this interference and excitement.

The reference points come first, and the quality of the linear power supply only second.
That’s why Vocm affects SQ that much. And that’s why both quality Vocm mod and quality power supply matter. But you will hear the latter only if you stabilized the reference points.


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So you see the capacitance across R6 as filtering noise that’s picked up by the 12V rail and carried through R5?

I got the notion during the early parts of this conversation that the Vocm pin on the opamp itself has varying impedance which drops enough to be significant in terms of the voltage divider, pulling what’s supposed to be a reference voltage downwards. Additional capacitance across the lower half of the divider provides a source of current to stabilise the voltage when Vocm impedance drops.

Is that mistaken?

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Okay, I found where I said wrong. I used generalization when said “cleaning power.” In fact, we’re stabilizing system: R5-Vocm_Input, which is Analog_Ref and not Analog_Power
And by “noise,” I meant the noise coming from OP amps in the first place.

To me, my sandwich still makes more sense than any single type of capacitors that anyone (here) used. Because we need to suppress these Vcom impedance drops in wide range starting at sound frequencies and as high as possible (because AD8132 works on very high frequencies). But the main target frequency is 22.5792MHz.


I apologize for the categoricalness with which I sometimes speak. please attribute this and some confusion this causes to the fact that I am using a translator because I am not a native speaker.


Researching the Sparkos regulators

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In terms of that local circuit that looks about right.
Not sure if the replacements would still like the output shunt capacitor or not.

Whether it’s a good idea in the context of the rest of the circuit I wouldn’t like to say.

Sparkos don’t mind

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Aye different folks say different things about that output cap on a regulator.
WHat value is C7 (out of interest)?

of course, if there are downstream local regulators for each section of the circuit changing the regulator may make no difference whatsoever :wink:

There are regulators downstream on all the boards.

I already have a dedicated power supply for the analog board, which gave a noticeable improvement. Without Vocm mod it gave a night and day improvement despite the fact that there are regulators downstream on the analog board. With Vocm mod, the difference is not that big anymore, but it is still noticeable. This is my experience with the ANALOG power.

Now, the point of this next stage of modifications is improving the DIGITAL power.

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I hope it goes well :slight_smile:

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A bit more unsafe all those considerations I guess since Ted can’t confirm due to his vaporization for still unknown reasons :wink:


opamp replacement
silver transformer
3 separate lps
the result is perfect

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