Just to wanna give a little background story
i bought this pcie card:
https://de.aliexpress.com/item/1005005901937820.html
difference to the mainboard out was minimal i would say... but i wrapped this thing like this:
https://www.head-fi.org/threads/best-low-budget-pcie-usb-card.972643/post-18119864 and placed some ferrite clamps on the sata cable going to the pcie card, these two tweaks actually made the pcie card sound better compared to mainboard usb, i get the feeling that only EMI/RFI is changing how usb sounds...
i also placed more ferrite clamps on the cables i use... i currently use a ifi isilencer + 2m cable + 30cm cable + diy filter + 50cm cable ... on each cable end placed a ferrite clamp, so 6 in total.... with 8 i get the first dropouts, this also improved things greatly
Now... with all these EMI/RFI tweaks you may noticed how high frequencys of your hifi get "tamed" and you can kinda reach a point where the sound "sounds dead" IMO this is the "standard" you wanna reach... after you reach that point, adjust your EQ accordingly to compensate some of the "dead sound" but it seems like emi/rfi is specially boosting high frequency audio (it always sounds like 10-20khz is affected) and we you get used to it you may even prefer it....
Now if someone is under the impression ferrite beads affect sound "negatively" and what you hear is not just a side effect of filtering EMI/RFI, then i accept your opinion but its after some testing atleast not mine opinion
i actually used a house curve for 2 years with tamed highs above 5-10khz ... (around -6db at 20khz) ... with many EMI/RFI tweaks i was able to adjust the housecurve (after the sound "deadening") now to only -3-4db at 20khz .... imo this speaks words
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this is that... now what i wanna get to:
someone in the head-fi thread recommended to use ifi isilencers and such filter directly in the pcie card
now this has actually a big pro:
1. my diy filter injects a external power supply, so the power filtering properties of the ifi isilencer are pretty much useless placed before the diy filter, when placed inside the pcie card, it can atleast clean some of the power used by the pcie card.... this seems to affect things positively
i also placed a chinese power filter
https://de.aliexpress.com/item/1005005201924413.html (this thing filters only power as it seems) into the second usb slot of the pcie card... again this seems to affect things slightly (the ifi isilencer made a 2-3 times bigger difference here, i dont recommend getting this filter, its crap for the price unless you want a aluminium case and only wanna filter power lines)
Now to the point... i wanna add some power filtering for the sister board for the above reason
a simple solution would be one larger cap like 470uF + 0,1ohm wire resistance and we get a lowpass filter with the -3db point at around 3khz, i guess this is still enough to affect things positively, tho no real comparison for a 1,5F supercap getting us a -3db point at 1hz BUT i think a supercap cant be used efficiently here, when i put a current limiting power switch in between i dont think the supercap is able to "backfeed" the pcie card... a simple (unprotected) cap would be able to
we could also add larger caps like 680uF (2300hz) or 2x 470uF (1700hz)