In light of this discussion where I was accused of being all like: "dude trust me as it’s surprisingly lacking in any sort of spec whatsoever from a site priding itself on measurements and objectiveness and the initial pitch feels intentionally vague" and requests from @Boops, @atomicbob and others out of curiosity in regards to this amp both subjective and objective, I figured I'd offer up some objective measurements and also discuss the history of this amp. Note that all variants of the EC Studio are sold out and it is unlikely that Craig will ever make one again. I really won't get too much into how it sounds, other than maybe a few tidbits related on how this came to be. This amp came to be from a project Leviathan that never really took off, or at least took off in another direction. Basically one day, some guy bought some high-end Tango amorphous core interstage and output transformers and asked Craig to build a 2A3 amp out of it. The special thing about this amp was that an interstage transformer was used in lieu of a interstage coupling cap. There was an attempt to build this amp for Changstar folks, but it turned out that Tango went out of business (they are back in business again) and this project went kaput. The Studio amp came to be as a result of using Tribute nano-crystalline core interstages and Cinemag outputs with a tertiary winding (a McIntosh design from long ago). The OG Studio may have sounded too solid-state or even dry folks expecting a tube amp, especially for those who heard a Balancing Act. Some people were disappointed and sold their Studios. Others kept them. @zerodeefex loved it and often remarked that most people didn't understand what it was trying to do. I like to remind people that it was called Studio for a reason. The tonality of the OG Studio was like the OG Schiit Ragnarok, except clearer and better in every way. I think when it came to tube amps, most people did not expect this tonality (not warm, not wet, not bloomy). Over time, it became too much of a pain for Craig to obtain the nano-crystalline interstage parts from Tribute. Tribute did commit to making them, but delivery timeframes had been too difficult to nail down and communications were sporadic, and thus I explored a Plan B avenue by sourcing interstages from Monolith on behalf of Craig. The last few Studios sold were the Studio M, the M indicating the Monolith interstages. Personally, I preferred the Monolith parts as they possessed better microdynamics and added a small bit of wetness to balance the drier Cinemag outputs, but at the expense of ultimate transparency. Really, at the end of the day, the differences weren't huge. It was still an Eddie Current Studio. I don't think owners are missing out either way if they owned one or the other. People think I'm full of shit, but trust me, boutique parts are difficult to obtain, take a long time to build, and take forever to ship across continents. This not to mention how DHL or El Lay customs fucked up and sent a box of transformers back to Belgium only for Monolith to have to resend back to me. This is my last amp with boutique parts. Never again. I have another custom 45 amp, the one with the glowy mercury vapor rectifiers, using these same Monolith amorphous interstage transformers, but with double C-core Lundahl outputs and no feedback. This amp is a bit more forward sounding, like the OG Ragnarok, but with slightly less bass control because of lack of feedback. This amp was basically a development prototype with hacked holes in the top plate, messy internal wiring, etc. The Studio 45 Custom came to be because of coincidence. Craig had metal remaining for one more Studio amp, but none of the original parts. I had a last pair of Monolith interstage transformers. Since Craig was in the midst of the Studio Jr and Studio B builds, I simply asked: build me a custom 45 amp using the Studio B transformers. In essence, what I wanted was something more akin to the Leviathan with the Tango parts. A tube amp with some solid-state sensibilities, not a tube amp that sounded like a solid-state amp (OG Studio). Of course the problem is that the Studio B output transformers were designed with the 300B in mind, something Craig quickly reminded me. The 45 tube's plate resistance is twice that of the 300B! Well, let's double the 45s up in parallel half their plate resistance. It is a Studio after all which uses x2 paralleled output tubes. Duh. A side note on the Studio B output transformers: the prototypes of these were the Advanced 300B Output Transformer found on Mable Audio. Craig suspects these were based on ancient Western Electric parts back in the day and reverse engineered by someone in China. I think last someone checked, they were out of stock at Mable Audio. Craig bought a pair and disassembled these transformers, and sent them to an OEM in China, along with a Cinemag with the tertiary windings. The OEM responded that they actually knew about these Advanced 300B Output Transformers and thus could easily replicate them. Not only replicate, but also add the McIntosh tertiary winding to it. Another interesting tidbit is in regards to the laminations: no exotic materials used, but the core laminations are interleaved with different metals, permalloy and M-6 (don't quote me, I could have this wrong in respect to the actual materials) to counteract hysteresis (the memory effect of how a transformer hates changing signals). Now there are no guarantees that such an endeavor will work. The double C-core output transformers from China for the second run of the Super 7 amps ended up sounding worse than the prototype and the first run's Transcendar EI parts. However, in this case it did. I was super worried that it would end up sounding like shit, but I sat and listened to these parts, apples to apples, and was satisfied that they sounded the same. Most of amp development is an art and through listening. I breathed a sigh of relief. Finally, a project Leviathan type amp that sounded like a tube amp. Either way, everybody wins because Craig's built so many different kinds of amps, each with slightly different presentations. If it sounds like this is too much talk about transformers instead of tubes or design principles, that's because the transformer makes the tube amp, at least the SET with no or minimal feedback. This is why I tell folks to roll transformers instead of tubes. It's also why Craig's amps sound good even with cheap new production China tubes. Measurements in a bit. BTW, I suspect the measurements from the Studio B will be similar on the account that these amps use the same output transformer. In fact, the Studio B may measure better than this Studio 45 Custom because 300B has more power and the interstage transformers may add more distortion than interstage caps. I will try to grab a Studio B for measurements when one is available. Either way, it will be interesting to compare this TOTL tube amp with an entry-middle level one.