Morning (for me at least). So, I have spent the last couple months playing around with output/signal and rectifier tubes for my TRP, and have also been trying to decide whether there is any reason to upsample. These are my results:
Output/signal tubes:
I have tried current production Gold Lion KT66,77, and 88 and ElectroHarmonix 6ca7. I have not tried (and likely will not try) any NOS tubes. For me, too pricey for a matched set of four (my dac is balanced), questionable origins and qc, and current production are great.
KT88s were terrible. Super detailed, but overly strident and non-musical. My reaction is not just a taste issue. I cannot imagine anyone liking these tubes with this dac. Thankfully, I have a Jolida integrated in a second system that uses these tubes as power tubes.
The other three were each excellent. i could be happy living with any one of these as my only tubes choice.
KT66 is linear, balanced, and neutral. They were the first tubes i tried and i was so happy with them that I did not explore other tubes for many months after receiving my TRP upgrade. However, as compared to the KT77 and EH, the midrange is a touch thin.
EH6ca7-Drop dead mid-range, extremely rich and liquid. Very natural and relaxed tone. Less air, high end extension, and punch than the others. I like a somewhat romantic sound and thus loved these.
KT77-Overall best/favorite of the four. Wonderful sparkly highs, killer dynamics, by far the largest soundstage (both in height and breadth), and highly musical. Midrange is very rich and juicy, not as extreme as with the EH, but close.
Rectifiers:
GEC U52-Linear, balanced, neutral, and dynamic. I have used this as my main rectifier for three years, both before and after TRP upgrade. Excellent tube. A touch thin, however, when compared to the other two i tried.
Potato Masher-Beautiful rich sound. Incredible for $15. I could easily live with it.
KR 5u4g Ricardo Kron-Excels at tone which is very natural and spot on. Rich midrange to boot. Exposed the potato masher as a touch off tonally (sounded a bit synthetic by comparison).
PCM v. DSD 512:
Prior to the TRP upgrade, i upsampled to DSD 512 with Roon and HQP. Despite it creating lots of cpu and networking issues (even with i7 processor on Sonictransorter built for HQP), I thought it sounded great and thus lived with the headaches. To me, 512 was significantly better than less cpu intensive 256.
After reading on this forum that PCM on the new engine 53 compared favorably to 512, i gave it a try. I have not gone back. PCM on this dac sounds as good if not better than 512. Actually, very similar sq but the PCM seems a touch more relaxed. I am quite happy to have get max sq qithoug maxing the limits of my server.
I have really enjoyed this forum and this thread.
Take care.