[b0bb]

Does this adjustment need to take place if you swap out for yellow bead tantalum cap as well or just the wet tantalum?

Measure the DC voltage in the XLR pins and the RCA outs.
If any of the measurements exceed 5mV, consider adjustments.

This is mandatory if your playback chain is DC coupled all the way aka no signal coupling caps.

 

[szrurs03]

Here is one way to increase the microdetail and soundstage of the 004.

The 2 pale green resistors with 1904 written on them are 5ohm Vishay VSMP Z-Foil
- Non inductive
- Non capacitive

Makes the near perfect candidate for the coupling resistors connecting the XO to the pair of 9038PROs

 

[szrurs03]

hello bob
Can these resistors be fitted for 9028pro.(5ohm)VSMP Z-Foil

 

[dna301]

b0bb, 5ohm value is ok with 950x?

 

[ESL57]

This thread is getting more and more interesting, this dac gives a lot of play for the enjoyment of the changes. Just remember that my tests were always aimed at solving the problem of random noise in DSD files recorded with low level, my 004 is not GEN1, better call it GEN0 (my pcb is different). Swap Vcom's Epcos capacitor for polymer-aluminum to hear it, definitely not the way to go, sure to have more current leakage than other types like wet tantalum, silicon or Teflon capacitors (these last 2 only manufactured at low capacitances). My goals are the same as most of you, low frequencies are not all the best (improve the analog power supply and it was not night and day either) and highs still a bit of digital harshness. I will follow your recommendations ... B0bb, I will remove that yellow 100nf and try the things suggested in the i / v stage.
I have been thinking after getting to solve some problems, to make a mod (super-mod anti-digital hardness), that I like and that tube lovers may like, an i / v stage based on vacuum tubes, maybe the variety of brands can better adjust the sound to the tastes of each user more easily, would be a very versatile mod, also there is space within our 004 to put an additional circuit, it would be necessary to design a specific pcb and add a small transformer.
Maybe some starting points:
https://hq-audio.net/products/pcb-pure-tube-i-v/
https://www.tubecad.com/2011/03/blog0203.htm
A lot of work ¿? Does this dac really deserve it?
Once the design is optimized it should not be too expensive an investment I think

 

[fmzip]

Measure the DC voltage in the XLR pins and the RCA outs.
If any of the measurements exceed 5mV, consider adjustments.

This is mandatory if your playback chain is DC coupled all the way aka no signal coupling caps.

Thank you sir! Do you recall which pot adjusts which output? You mentioned adjusting the XLR's first

 

[ESL57]

Thank you sir! Do you recall which pot adjusts which output? You mentioned adjusting the XLR's first

In this photo the yellow zone is the offset adjustment of the left channel balanced and the white unbalanced and the red and green equal in the right channel, a period of thermal stability of 15 min is good to wait for the adjustment and as B0bb says: first adjust them balanced. But first of all I would verify that the analog power rails are exactly balanced, GEN1 + 15.5v and -15.5v.

 

[fmzip]

In this photo the yellow zone is the offset adjustment of the left channel balanced and the white unbalanced and the red and green equal in the right channel, a period of thermal stability of 15 min is good to wait for the adjustment and as B0bb says: first adjust them balanced. But first of all I would verify that the analog power rails are exactly balanced, GEN1 + 15.5v and -15.5v.

Thank you! I am a novice at all this and appreciate the exact details.

Can you explain where to measure these rails please? Do I take the measurements in the red area, assuming that's the op amps? I see from @b0bb post that the grey pots are for these adjustments, is my board a Gen1?

 

[ESL57]

Thank you! I am a novice at all this and appreciate the exact details.

Can you explain where to measure these rails please? Do I take the measurements in the red area, assuming that's the op amps? I see from @b0bb post that the grey pots are for these adjustments, is my

Thank you! I am a novice at all this and appreciate the exact details.

Can you explain where to measure these rails please? Do I take the measurements in the red area, assuming that's the op amps? I see from @b0bb post that the grey pots are for these adjustments, is my board a Gen1?

That not are op amps, they are dual transistors, because of the size of the heatsinks I think your pcb is GEN2. Down here my "GEN0"

 

[fmzip]

That not are op amps, they are dual transistors, because of the size of the heatsinks I think your pcb is GEN2. Down here my "GEN0"

Thank you. I revised my image to match yours. Now the only question remains, what should I dial in my voltage to be at +15.5/-15.5v? I'll post my findings this evening.

 

[fmzip]

@ESL57 @b0bb I measure -15.46 +15.46, do I need to get that to 15.50? Needed a bit of adjustment on the xlrs thanks for the tips!

Those black pots need to be replaced for something more robust

 

[b0bb]

@ESL57 @b0bb I measure -15.46 +15.46, do I need to get that to 15.50? Needed a bit of adjustment on the xlrs thanks for the tips!

Those black pots need to be replaced for something more robust

That is fine getting to 15.46.

 

[b0bb]

Thank you sir! Do you recall which pot adjusts which output? You mentioned adjusting the XLR's first

@ESL57 covered those.

 

[b0bb]

b0bb, 5ohm value is ok with 950x?

That will work.

 

[b0bb]

https://hq-audio.net/products/pcb-pure-tube-i-v/
https://www.tubecad.com/2011/03/blog0203.htm
A lot of work ¿? Does this dac really deserve it?
Once the design is optimized it should not be too expensive an investment I think

The other way around, the designs mentioned not good enough for use with the 004, output impedance of the tube is way too high to drive the passive LPF.
LPF on 004 expects to be driven from a very low impedance source.

If you are looking for additional smoothness replace the Accusilicon AS-318B with the Crystek CCHD-950X

Check with @fmzip who has made the switch, I think @fmzip gave away the AS-318B after trying the CCHD-950X
Also try replacing the noise filter caps used by the TPS7A47 and LT1763 regulators with film caps, this reduces harshness due to the fridge magnets* LKS used

*the horrid ceramic caps LKS installed on the board, make good fridge magnets if you grind them up, add it to a latex base and magnetize it.