[oldearwax]

Check the DC offset voltage between the +ve xlr terminal and turn the trimmer of the corresponding opamp until the difference is below 5mV
Repeat for the -ve xlr terminal, repeat for the other channel.
Double check the DC offset on the RCA outputs and adjust the associated trimmer of its opamp if required.

The opamps are straight thru meaning left most opamp connects to leftmost xlr pin

Thank you b0bb !!
I read your instructions carefully, but I lack understanding of balanced output offset voltage adjustment.

Is the idea to ~zero the voltage of each xlr terminal wrt ground
(of each channel) with the corresponding trimpot ?

So I drew up a block diagram to summarize what I learn/know so far (errors in the diagram are all mine).

LKS-004 has two ES9038.
Each ES9038 has four outputs (L, R, LB, RB), how are they connected to the op amp ?

 

[b0bb]

Is the idea to ~zero the voltage of each xlr terminal wrt ground
(of each channel) with the corresponding trimpot ?

Yes

Each ES9038 has four outputs (L, R, LB, RB), how are they connected to the op amp ?

One chip for each channel, each 9038Pro runs in mono mode (L + R, LB + RB)

 

[MartinWT]

It's finally done - I decided to spend my Sunday afternoon wisely.

Below, you can see the four original 0.5W I/V resistors (much smaller ones mounted under the PCB) have been replaced by Vishay CPF3 61.9Ω 3W resistors mounted on top next to the capacitors. There is little room underneath with the heat spreader bar so I thought they would be better mounted on top.

Secondly, the two large electrolytic V_com capacitors have been replaced by two low leakage 100uF 10V tantalums.

I've only just reassembled it all and got it hooked up to the system, so it's early days and the new components will need some burning in. However, right from the off I can tell that this is going to be the final icing on the cake. There is no overall change in balance or presentation, or even detail, but there is a clarification of the image, a reduction in slight blurring when the mix gets busy, and further tightening of the bass (the effect of the V_com caps). There is also the removal of the tiniest 'sheen' to the proceedings, giving further insight into how strings are plucked, enunciation of vocals etc. It's a small thing, noticeable on some vocals but not others.

I really like this DAC, it suits my preference for how music should be portrayed. I find myself listening more these days, rather than less, indicating that the essentials are all in place. My thanks go to @b0bb and @Xoverman .

 

[wersuss]

Stock mh-da004 tends to be cold/bright.
I copycat B0bb's wet tantalum capacitor 150uF upgrade.
Got the wet tantalum from
https://www.mouser.com/ProductDetail/Vishay-Tansitor/109D157X9010C2/?qs=GDo1UeZ%2BmvIxv47/FOPtLA==
The original cap is a 12uF noname "black" cap.

This mod totally removes the edginess of mh-da004, it puts/shifts emphasis to
the more pleasing mid range and bass, but it also surrenders a tiny bit of top end.
It sounds more relax and as Xoverman said one can listen to it for a long period of time.

Thank you B0bb !

Would these work? https://www.ebay.com/itm/2-pcs-SPRAGUE-109D-Wet-Slug-Tantalum-Capacitors-150uF-30V/284021664990?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
109D Wet Slug Tantalum Capacitors 150uF/ 30V

 

[oldearwax]

Would these work? https://www.ebay.com/itm/2-pcs-SPRAGUE-109D-Wet-Slug-Tantalum-Capacitors-150uF-30V/284021664990?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
109D Wet Slug Tantalum Capacitors 150uF/ 30V

See Post #3,271, b0bb's advice.
Wet tantalum may dry up after some years, I guess.

 

[fmzip]

Delete...

 

[b0bb]

See Post #3,271, b0bb's advice.
Wet tantalum may dry up after some years, I guess.

The cap is quite old the rubber seal integrity is suspect, must avoid the electrolyte seeping out as the cap warms, it is highly corrosive.

 

[fmzip]

It's finally done - I decided to spend my Sunday afternoon wisely.

Below, you can see the four original 0.5W I/V resistors (much smaller ones mounted under the PCB) have been replaced by Vishay CPF3 61.9Ω 3W resistors mounted on top next to the capacitors. There is little room underneath with the heat spreader bar so I thought they would be better mounted on top.

Secondly, the two large electrolytic V_com capacitors have been replaced by two low leakage 100uF 10V tantalums.

I've only just reassembled it all and got it hooked up to the system, so it's early days and the new components will need some burning in. However, right from the off I can tell that this is going to be the final icing on the cake. There is no overall change in balance or presentation, or even detail, but there is a clarification of the image, a reduction in slight blurring when the mix gets busy, and further tightening of the bass (the effect of the V_com caps). There is also the removal of the tiniest 'sheen' to the proceedings, giving further insight into how strings are plucked, enunciation of vocals etc. It's a small thing, noticeable on some vocals but not others.

I really like this DAC, it suits my preference for how music should be portrayed. I find myself listening more these days, rather than less, indicating that the essentials are all in place. My thanks go to @b0bb and @Xoverman .

Nice work. Curious, how warm are those 3W resistors getting? Was wondering why they were put on the bottom side of the board in the first place and not the top

 

[MartinWT]

Nice work. Curious, how warm are those 3W resistors getting? Was wondering why they were put on the bottom side of the board in the first place and not the top

Good question - they were small 0.5W resistors placed where they would get hot. I haven't touched the new ones after a good warm-up, so I can't tell but I do know they will be stable in the air of the main chassis as I cover the top vents by more than half to stop them ringing like chimes. Dynamics are up so they don't suffer as much from thermal throttling.

@b0bb I meant to ask if the blue parallel I/V caps are worth changing for anything better?

 

[fmzip]

Good question - they were small 0.5W resistors placed where they would get hot. I haven't touched the new ones after a good warm-up, so I can't tell but I do know they will be stable in the air of the main chassis as I cover the top vents by more than half to stop them ringing like chimes. Dynamics are up so they don't suffer as much from thermal throttling.

@b0bb I meant to ask if the blue parallel I/V caps are worth changing for anything better?

Are these the resistors you used? Need to take my unit apart to check the values, is yours version 2 of this DAC?

https://www.mouser.com/ProductDetail/Vishay-Dale/CPF361R900BEE14/?qs=kPTqIjks3ML4M3KHaSCR3A==

 

[MartinWT]

Are these the resistors you used? Need to take my unit apart to check the values, is yours version 2 of this DAC?

https://www.mouser.com/ProductDetail/Vishay-Dale/CPF361R900BEE14/?qs=kPTqIjks3ML4M3KHaSCR3A==

Yes, exactly those.

I'm not sure of the version, but the old resistors were close in value (62 point something).

 

[b0bb]

@b0bb I meant to ask if the blue parallel I/V caps are worth changing for anything better?

It depends of your preference, for something smoother try a polystyrene cap, if you prefer a brighter and sharper presentation try a Corning CGW Glass Cap.

 

[oldearwax]

Per b0bb's suggestion,
I re-adjusted the offset voltage of each op-amp after the Vcom 109D Wet tantalum cap replacement.
I wrote down the voltage of each terminal before and after the adjustment (see attachment).
Just a few milli Volt makes a big difference in sound.
Strongly recommend this adjustment after the Vcom cap mod.

 

[tdrood]

LKS changed to ceramics on the Gen2.
Ceramics have low ESR but lacks the ripple current capacity.
Need the current capability to drive the very long trace lengths on the 004, seems like a very odd choice to go to ceramics.

I swapped the stock 470uF to 820uF with about 3x increase in ripple current capability, there is still a ceramic bypass so ESR is not expected to be an issue.
The 820uF is a newer line of the FP cap series

Ok, so I am collecting parts to do these mods, and I have the DS90LV032A, but it looks like there's an smd cap in there. I haven't pulled the amanero assy back out, so I don't know if there's any provisions for an electrolytic under there. Is this what yours looked like pre-mod? If so, what cap should I select for this location. Sorry for being a pita...

 

[b0bb]

Ok, so I am collecting parts to do these mods, and I have the DS90LV032A, but it looks like there's an smd cap in there. I haven't pulled the amanero assy back out, so I don't know if there's any provisions for an electrolytic under there. Is this what yours looked like pre-mod? If so, what cap should I select for this location. Sorry for being a pita...

Your board is different from mine.
A better photo showing the cap looking directly from top down is needed.
The side view obscures any sign of the potential mounting holes for the electrolytic cap.