I think I recall the mk1 having conductive adhesive foil in places I had to reinstall on digital card. Probably more robust and repeatable than a bonding finger that gets bent or breaks and one of those things technicians take little heed to placement like the would tape. Failed error proofing the bane to assembly. It is hard to implement without variability often
Conductive adhesive is not as good as these fingers. The adhesive acts as an insulator.
These fingers are quite good if properly fitted. The Ethernet has the same conducive copper tape as the USB on the MK1.
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Nicely done Jeff. A really good catch.
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Maybe we could entice Jeff to do PSA QC!
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So how obvious is this issue? Do people really need to go and look? How bad did the sound really get?
It’s not a problem in general. I only brought it up as a remote possibility that vmax might be able to use to explain his system’s strange behaviors. In general, if the finger is bent (or broken off), the worst that can happen is that the ground differential between the DAC and equipment that doesn’t have a safety ground will grow a little. There is also a safety bidirectional transient voltage suppression diode which will limit the differential to about 25V so that no equipment will get damaged. If the sound is worse than not lifting the ground on that input, don’t lift the ground on that input - since the other end of the cable isn’t connected with any safety ground and hence there are no ground loops, the best thing to do is to provide a ground anyway.
[Edit - I guess I should have clarified that the finger is only there for potential EMI mitigation.]
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I didn’t notice any difference in sound. I just noticed they were not doing what they were designed to do and corrected it when I installed our 2nd set of prototype transformers. OCD???
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Something I also noticed is PS Audio did a great job of isolating the signal grounds from the chassis. These isolation washers work great. Even the i2s screws have insulator washers.
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I grounded USB the bass is stronger highs a get less than galvanically isolated . So far sound drifting into harshness has cleared up. I am thinking if there’s a bent finger might be on the USB input . Waiting to open DAC and check all digital input grounds when I get a fresh sheet of AB7050HF RF and EMI absorber which should arrive this week. I will apply internal and directly to ICs and ribbon cable where accessible and over half of the toroidal transformer on interior of lid.
Below is whst helps MK2 most and confirmed by @dchang05 who also tried running without it again.
The absorber placed outside on lid. Seems to improve the areas that Adrian liked MK2 less than MSB. Taking it away things are less open, narrower sound stage, thicker highs, less defined bassless clear mids and highs. The Mk2 is a different DAC with absorber more effective than galvanic isolation for sure.
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Thanks for this. I’ve read about using EMI absorber but have not felt comfortable sticking stuff on the inside of my DAC when I know so little about electronics. I just want to make sure that I understand right; what you suggesting in this diagram goes on the outside of the lid. I’d be more comfortable with that (even though I would have to remove the plastic from the lid 
, which I never do with my PSA gear [except amps]).
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I put them on top of the lid so you can remove them if you don’t like the effect with one or both pieces. So is vmax, I believe. The only difference on mine is instead of 3x4, mine is 2x4 on the T section. I like the SQ with them on top.
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Yes on the outside of lid. I don’t stick it down. Just let it lay on top of the plastic. I slways do this to tune the sound before popping lid. It works better adhered directly to electronic components or inside the faraday cage of a unit. But is quite efficient externally in larger pieces.
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Thanks for that post it caused me to look at T leg. That was why I wasn’t digging the grounded USB. When I replaced the T leg I had not pushed it out to 3”. My system needs that extra inch. Also helped bass get more defined and opened mids and highs back up to my system preferences.
What was it doing in your system at 3” versus 2”?
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When I used 3" the SQ is a bit “thicker” to my taste, and 2" gives a better balance. I have so many tuning supports under gears and power cords now that I may go try 3" again. I have a 1" dry strip somewhere.
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It’s odd shorter sounds thicker on mine the 3” is just right. Even if I find the grounding finger bent internal. I am really likes USB without the ground lifted snd absorber T leg at 3”. Plus it doesn’t drift off. Might be the Inakustik Referenz pure Silver Air. It seems to be doing everything right. The salesmen said to try it grounded and galvanically isolated. Its a waste of good dilver grounds in the USB to not drain it out siver grounds on the Whisper power cord of the MK2.
The T is 2” wide, and 4” long towards the middle. I thought yours is 3” wide right? I grounded all inputs and output, but leaves the shell lifted.
Tonight I made some adjustments on vibration supports, and the SQ is amazing. The new cords probably helped too.
Okay I was not pushed out to 4” only 3. I saw i had a crease where I tried it thinner. Hopefully you have perfected everything then. I still have bed supports to try on power cords and USB for vibration stabilization. But good to go slowly.
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This material you added is over the display / power transformer and the two FPGA’s.
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I find all this sad.
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Yes. Also over ribbon cable between display board and digital card.