I am not doing a full blown review of the Cavalli CTH (compact tube hybrid) - but I will post my impressions so far of its sound and a few comparisons.
I have spent a couple of days with the CTH/Mullard short-plate and find it to be a nice detailed and warm powerful tube hybrid, with above average soundstage and no glaring negatives or complaints in the sound. My main complaints are the lack of a power switch, no RCA input on the rear, and less transportability due to the protruding 12AU7 through the top cover.
I spent some time comparing it vs my Head-direct EF1/stock RCA clear-top 12AU7. One observation was with Giovanni Mirabassi "Prima O Poi" the song Symphomaniax - With HD600 the CTH presented more body to the trumpet, the piano was smoother/refined and more up front, and the sound was mellower overall and slightly darker. But, the sound was also fuller and more refined like you would expect from a bigger amp. In general listening to the CTH was more engaging than the EF1 with stock tube, which seemed a little more distant and presented a slightly less solid image of the instruments.
Switching the EF1 RCA clear top to a Mullard long-plate in the EF1 resulted in the two amps coming much closer together. The EF1 picked up more body and refinement, and became more engaging as well. With the Mullard in the EF1 the treble did become a little more recessed than with the RCA, but not lacking. At this point I cannot pick one amp over the other as the two sound very similar. The volume control on the CTH is much better than the EF1, and I am now convinced that I need to send the EF1 back to have the volume control looked at.
I also compared the CTH to the ALO/RWA Amphora which seems to have a little bit more transparency and detail and yet still has a fairly rich tube-like sound similar to the Cavalli. Yes, sound signatures are somewhat similar but they are not exact. I have not been able to compare their soundstages or bass/treble extension with test tones yet, but I can say the Cavalli has a little too much bass with the Sennheiser IE8 which sound better on the Amphora. I still don't think I would change anything about the Amphora or CTH with most headphones. With the Grado RS-1 the CTH, EF1 and Amphora also seem to come closer to each other in sound. (can't use the IE8 on the EF1 due to the volume control).
Most of the listening has been with my iMod and portable Vcap dock as source (using Soloz 12-strand Litz-braid mini-RCA or my ALO SXC mini-RCA). The RSA P-51 Mustang was velcro'd to my portable Vcap dock, so I tried it out in comparison too. The P-51 has slightly more treble presence than the CTH or EF1 with Mullards or the Amphora, so it's not quite as mellow as them, but that is about the biggest difference. The other thing you notice is the P-51 is a little more forward and energetic or aggressive sounding, but not in a bad way. The CTH, EF1 and ALO Amphora are a little less aggressive and more refined sounding than the P-51, but the P-51 holds up well against them.
The CTH is a good sounding amp and well worth the money and time to build one, and that is all that matters. I (and others) hate ratings, so I am going to nip the requests for one in the bud. Don't ask me. As you can see from my comparisons, it competes well vs other amps costing more, and as an added bonus it can be used with IEM while my son's Millett SSH and my EF1 cannot, due to poor volume controls. (Millett SSH not compared directly this time around)
