Finished the new node a few days ago and it’s working perfectly. The audio quality is outstanding, not the slightest hint of a buzz, hum, clunk, etc.
To make a full-duplex node using high quality FCC-certified radios as cost-effective as possible I’ve also been looking at lower cost HT options, since the FT-530’s go for ~$150 and can be hard to find. I noticed recently that QRZ and gigaparts have a new radio, the QRZ-1, which although Chinese is actually FCC-approved. Turns out it’s a copy of the Retevis RT85, possibly with some changes to the menus. The RT85 are known as “Baofeng-killers” due to their costing only slightly more but having much better RF performance. You can get 2 RT85’s for $50 with free shipping & free returns on amazon. For a simplex node you’d need just one but at only $25 for a 2nd radio that’s quite a low price to add cross-band full-duplex capability. I ordered 2 and will see if they are able to offer a similar level of audio quality and cross-band RF performance as an FT-530.
If so that would mean a high-quality full-duplex node could be built for as little as: $48 (Dell 3040 microPC) + $35 (DRA-30 kit) + $50 (Pair of RT85s) + maybe another $50 at the most for a power supply for the radios and various cables/wires = a grand total of under $200 for a node with far higher audio and RF quality than any commercial node on the market. An optional case, enclosure or maybe a 1U rack shelf could also be provided to hold everything securely and make the whole setup more portable.
FYI the 530 and probably most other HTs do need a well-filtered power supply. I suspect most HTs are intended to primarily run on battery power and thus don’t have much if any filtering or regulation. I have an old Yaesu NC-72B which puts out 12V 500mA which is plenty to run the HT in low-power, but some buzz would come through, which also happens even with an Astron VM-35M. I had an old homebrew variable 5A power supply with a blown transformer so I put the NC-72B in that and its 40mF of capacitance knocked out the ripple, and steps the voltage down to about 6-7V where the HT stays very cool even during 100% duty-cycle TX.