Usefullness of a external quality power (linear PSU or Battery) for USB Pci card (SOTM, PPA,...) for use with an Asynchronous, completely 5V decoupled DAC ?

[Hifidelit]

It depends on the card design and what you are connecting to. If we take the JCAT usb card then the design is as follows (from Marcin):

The JCAT board has a linear regulator which can provide additional filtering to the NEC chip. However without 5V connected, the 3.3V from computer will be applied directly to the NEC chip without much filtering. Even without a linear 5V power supply it might be better to connect 5V from computer. To sum up: even for self-powered USB devices, the JCAT USB card will benefit from high quality 5V PSU. 3.3 is not used to power the NEC chip if 5v is applied.

 

Nige200 asked:

So you can tape over the 3.3v pins on the jcat card and supply via molex to prevent noise contamination from the motherboard to the clock and usb chip?

Marcin replied:

The 3.3V is still used for 1.05V regulator for the NEC digital core. We wanted to use only 5V but it was not possible due to power dissipation.

http://jplay.eu/forum/jcat/jcat-battery-psu/

 

Pearse (sligolad) mentioned this tweak on the usb card thread:

 

The one benefit of the cheap ebay riser cables is that if you have a 3.3v linear supply you can break into the wiring on the riser cable and cut the 3 off 3.3v lines and supply these direct off the 3.3v linear supply.

I found it a nice improvement on the JCat USB card to feed it directly off the Teddy Pardo 3.3v Linear supply and have no 3.3v feed off the Mobo with all the junk on the Mobo supply even with all linears to the ATX supply.

All my grounds are on a switch so the JCat card is powered only when I switch in the grounds at power up and all works fine with a cleaner sound supplying the 3.3v for the JCat off a linear supply.

 

http://jplay.eu/forum/jcat/jcat-usb-card/page-10/