Hi folks. I completed the build of my S.E.X. late last week and it went without a hitch. All resistances and voltages checked out right on the money and I've been able to get in a few hours of listening time on it so far. I'm using Alpha Primes with it, and am coming from a Schiit Lyr (and a Crack/Speedball with DT770/250s). The S.E.X. is wired for 32ohms right now, until I install the impedance switching kit. The amp sounds pretty great right off the bat - great authority, spaciousness and beautiful sounding bass and lower mids. I sense though that everything isn't quite perfect. It's a little hard to describe, but the sound seems a little bit "boxed in" often, but somehow it does this while maintaining good separation and a nice soundstage... It seems kind of like the upper mids or lower treble is a little down (don't quote me on that...), and possibly there is a tiny bit of what sounds like reverb that is always present. These are pretty subtle which is why I'm having a hard time describing them, but the overall effect is that the sound doesn't quite reach the airiness that I was expecting. I have not yet had a chance to go back and compare the sound with my Lyr but this is not a characteristic I noticed on that amp. There is so much I'm hearing in the S.E.X. that is fantastic, I would really like to figure out what I'm hearing and hopefully resolve it.
Since the electronics appear to be working properly, I'm wondering if this could be a tube issue (either less than great tube or not well matched). I have swapped the tubes (L/R) and it seemed like the "weighting" of the sound shifted subtly from my left ear to my right. I've covered each ear and listened to just one side at a time and it's not enough of a difference that I can discern it doing this. I also left the amp running (and playing music) all night one night to make sure everything was fully warmed up; I think there was a slight improvement but the overall effect was still there. Also I attached some speakers to the S.E.X. (which is wired for 32ohm right now so it's not really optimized for this use) and noticed the same type of sound signature (a little "boxed in"). FWIW, the two tubes I received with the kit are different brands and slightly different construction (one has a small wire connecting the heaters that runs across the top of the tube interior, the other doesn't have this). I have ordered a few more 6DN7s on eBay so that I can try swapping them around to see what happens.
What I'm mostly looking for here is some feedback as to whether the sound impact I've described (slightly boxed in sounding, quite subtle reverb-ish quality) could be ascribed to tubes or if I should do any kind of analysis on the rest of the amp. I still have the C4S and impedance switch kits to install and will likely go ahead with those steps unless someone says here that I should be troubleshooting something else before doing that.
Thanks all for any feedback. Despite what I describe above, I still sat and listened to music via the S.E.X. with a huge smile on my face way too late into the evening every night this past weekend. This is a wonderful kit and I feel as though I'm on the cusp of (for me) end game sound.
-John
P.S. One small question I forgot to ask: what is the red heat shrink in the base S.E.X. kit intended for? I didn't encounter any call for it in the assembly instructions...
