Tonally these two tubes are pretty much identical. Both have a very flat response and not overly 'Tubey' in their sound. To clarify the 'tube' sound to me is a bit rounded and punchy in the mids. Sometimes 'tube' sound is a bit soft on the details and the trade-off is pleasant to listen to. Many would argue this, but I'm talking about cheap common tubes. To my ear they typically fall a bit short.
I gave each pair 1/2hr to warm up. Both are well broken in. The CCa with maybe a few hundred hours on them, the Russians have 100hrs of break-in time only. They might get much better with time, but I don't know.
The Russians are slightly more intimate with an ever so slight emphasis on warmth over the Siemens. Both allow you identify placement and certitude of instruments with ease. I seem to be mostly focused on sound stage these days. Space and art of envelope layering by the artists. So I'm going to focus here rather than anywhere else, other aspects being negligibly equal.
Renmin Park - Track 08 - Cicadas
This track brings to life live samples from ... presumably Renmin Park... and layer on top of that voices in the presence range. Then it layers sound samples upon samples all with different sound envelopes. This track sounds great with both tubes, the only advantage the CCa has is that the deep background sounds way in the distant are more pronounced. There is a church bell that faintly goes off and you can almost hear it echoing off the roof tops and through the streets to reach you. With the voskhod this is less pronounced but still can be sensed. Then again I might impressing my experience of the former on the latter.
Renmin Park - Track 02 - Renmin Park
I discovered this track with my current rig and CCa tube. I have to confess that for me, I don't know what it is but there is something in this track gets me. The first time I heard it I teared right up. Sometime it still gets me. But emotionally the CCa brings this out in me. The Voskhod falls ever so slightly short in this respect. I'm _very_ surprised by this and I can't really explain the difference. So there you have it. One tube produces more of an emotional response than the other. Go figure. If that isn't an element of je-ne-cais-quoi, then I don't know what is.
I think what might be going on here is that the E1CC88 might be a better fit electrically into the Lyr's circuit. You would think you could just add a hair more gain on the volume pot to compensate with the 6N23P. The problem being is that your bringing up the floor as well when you do this. The CCa being designed to be a sensitive tube fits the Lyr perfectly. Background and detail shines and I don't think a CCa can be beat in this respect.
Not that the 6N23P is a slouch in this circuit. No sir. The experience is nearly the same. If I didn't know the CCa I might even call this an end game tube with for this amp and headphone. Not that I believe in the nonsense of 'end game'. No such thing.
So the verdict in my IMHO is that the difference is very small. The cost difference very high. The CCa gets you 'there' a little more. A little closer to the recording. It's only evident if you A/B or if you are already ruined by the CCa. As one has been tarnished by the CCa tube I do notice that little niggling thing that I can't put my finger on is missing. That niggling feeling faded as I lived with the Voskhod for a week.
Also as Rob has stated a few times, it depends on your source. Perhaps the Voskhod does better than the CCa when it gets a different source to work with. So in the end its all plastic. Impressions aren't worth much and YMMV.
Edited by NightFlight - 9/14/13 at 5:11pm