Just some day 1 thoughts and musings:
First off, I love the build quality and the aesthetic works for me. I previously owned a Primaluna amp and my understanding is that these were (at least at one time) built in the same factory. The paint finish reminds of the Primaluna. I like the thick solid front faceplate with the cutout. The Cayin nameplate is a littly blingy but I have something similar on my Luxman, so sure why not. The umbilical cord is impressively substantial and gives a very solid industrial aesthetic. The switches can seem a little insubstantial next to all the rest of the build. VU meters are fun retro touch. Using an orange light is a good match I suppose for a tube amp since some of the light comes up through the driver tube sockets and at least it kind of matches tube glow.
it's interesting to hear the these 300b tubes warm up, with all the pinging they do. It kind of makes me think of the old radiators in grade school that would clang, but this is much more musical sounding
I did most of my listening with the stock tubes, but I briefly do some rolling. The first thing that came across to me was the soundstaging and how expansive it was. The second was that there was a bit of extra warmth in the bass, which could be quite pleasing in many cases, but a bit too much on some tracks that already had some prominent bass.
I know there have been discussions in the past about the XLR vs. RCA inputs and that the XLR input will go through a transformer to convert the signal to single ended. The purist in me wants to just use RCA and bypass addition al component, but reality is not so cut and dried. For one, it depends on the quality of the respective outputs on your source component; some DACs are know for having one output better than the other (e.g. Yggy is supposed to have much better balanced output) so it would clearly make sense to use whichever was better from your source. In my case, I am using a Holo May DAC which has separate circuitry to power the single ended and balanced outputs. I also had sets of same length Norne Silvergarde S4 interconnects in both RCA and XLR. I could flip back and forth between RCA and XLR inputs. Obviously, there is a volume difference so I had to compensate by adjusting the volume. This brings me a bit to the stepped attenuator. I believe it's 24 steps and from reading earlier posts, there was also a design compromise to balance the gain between steps to handle HP volume changes as well as speaker output volume changes. I'm sure I'm not the only one who wishes there were more steps or it was a non-stepped attenuator, but undoubtedly there are always cost/performance tradeoffs. Because of the jumps in the stepped attenuator, I wasn't able to quite level match between the two inputs since it seems to be somewhere in between the gain of 2 and 3 steps of adjustment (and it's tricky to do anyway). All of that being said, I didn't find a significant difference between the two inputs. So my recommendation would be use whichever is the best output your source has. The only other potential consideration is the additional gain the XLR input provides. If you need more gain, than XLR might be beneficial; if you want finer control between steps in adjustment, then go with RCA inputs. I did have some potential concerns that since my DAC (and I know others e.g. DAVE) run much higher output levels than standard and whether or not that could overload/saturate the input transformer, but again, I didn't find anything that concerned me.
I know this was noted in previous discussions, but I don't recall the explanations for this, but maybe someone can clarify regarding he power output from the various outputs with the different impedance settings is curious to me. The amp outputs 1.8W/2.2W/3.7W on balanced, 1.1W/2.4W/5.0W single ended for the L/M/H impedance settings. Why does the single ended have higher output power on M and H compared to balanced and why is it so much lower on single ended? Any why is the speaker output able to do 8W? I assume this all has to do with how the various taps are coming off of the output transformer, but it makes me wonder what compromises there are with such a discrepancy between single ended and balanced output and both those vs. the speaker output. personally, I don't have a use case for speaker outputs (although I can certainly understand if others do), so my personal preference would have been to just be a pure HP amp focused on optimizing that performance (e.g. the Viva is unapologetically a headphone amp only). Although I certainly can't blame Cayin for including that feature because there are no doubt plenty who would be unhappy if that option hadn't been there. But again, I still wonder about some of the compromised that might have been involved (e.g. stepped attenuator is another).
As far as tube rolling went. I did mention that I found the stock WE6SN7 tubes seem to have a bit of extra warmth in the bass (and possibly some rolloff). As a couple examples, in Girl from Ipanema which seems to be recorded a bit thick to begin with this began very thick. Similarly with Holly Cole's Tempatation, bass would get a bit thick. I tried switching in some Melz 1578 (appear to be 1979 vintage) that I also purchased from Level5. this seemed to tame that added warmth a bit and perhaps provide a little bit more subbass extenstion, but I really need to test out. These tubes seem to sputter a bit so these may have to go back. I also briefly tried some TS BGRP 6as7g via adapter, but to briefly to have an opinion. I have a pretty decent collection of 6sn7 so I'll have some fun rolling.
I'm very interested in tube rolling the 300b tube. In my Viva, I'm using a PsVane ACME which I like a lot (only tried the stock and a Psvane Treasure Mk. II) and I know others have posted the 300b is quite good. Someone mentioned to me that Torq likes the Western Electric 300b new production, but it doesn't seem like anyone on this thread has posted about it. If you have used that, I'd be interested. Elrog would also be on my list, but I read that they can be a bit analytical, which is probably not what I'm looking for. In any case, I'd love to hear some recommendations.
Regarding rectifier tubes, I know rolling those have been briefly discussed and I'm probably not that interested in rolling those, but how do you know when to replace them? Is it only when they fail or is there some other indicator? Do you replace them in pairs (and which way left/right or front/back together) or as a quad?
@jambaj0e as to your questions about LCD-4 and Susvara, I thought the LCD-4 worked fine and sounded quite good, but the bass was probably still a bit loose compared to SS or more power amps (e.g. Viva), but I need to do more listening, but again, still very enjoyable. Note that I use oratory EQ which also has a -8.3db level compensation, but it still did fine. I did not think the Susvara sounded very good. It could sound quite congested and the bass became a bit wooly and thumpy. This was one of the primary reasons I bought the Viva because it was one of the few SET amps that could drive the Susvara adequately. I used XLR input to maximize gain and tried both RCA and XLR out as well as the different impedance settings. I also noticed that even at moderate volume the VU meters were pretty much pegged at 100. I don't think this is a good pairing. However, with the HEK SE which has very moderate power requirements, I thought this was a very enjoyable combination - plus the soundstaging ability of the HEK SE with the amp made for a nice combination.
in any case, that's probably enough for day 1, lol.
Info on my setup:
Roon (local files, Tidal, Qobuz) -> HQPlayer (sinc-M upsampling up to 768K, sinc-M, LNS15) -> Sonore UltraRendu -> May DAC (NOS mode)
Headphones primarily used: LCD-4 (EQ'd to oratory settings) and Norne Silvergarde S3, Susvara (with Dekoni FSS pads) Norne Vykari, HEK SE with Norne Silvergarde S3