I have the EC Studio Junior pre-production in the house to help Craig troubleshoot some issues. This amp is configured with 300B tubes and uses feedback from the tertiary winding of the output transformers. The most significant difference from the AF is the output transformer. The SJR transformer is a custom deal, not the Cinemag used in the AF. It was based on a pre-existing transformer (quite pricey). This original transformer was taken apart, disassembled, and dissected to discover the secrets of its core laminations. The tertiary winding (based on an old McIntosh design back in the day) was then put into this transformer. I've heard both the original and tweaked with tertiary winding version and I can say that have the same or similar sound. The experiment was a success. The AF transformer is slightly drier. The SJR transformer is slightly wetter and richer. A most important change with the SJR transformer is the availability of 4-ohm and 8-ohm taps. The headphone out uses the 8-ohm tap only. The output impedance from the 8-ohm tap is probably 2-3 ohms, and the 4-ohm probably just a little over 1-ohm. Don't quote me on this. These are just predictions. The speaker outputs are Neutrik Speakon (the best thing ever - used by pros - screw you audiophiles with your lame gigantic lugs and banana plugs that tend to break shit more than offer better sound). Pin 1 +/- are the 8-ohm taps and pin 2 +/- are the 4-ohm taps. The reason this transformer has a 4-ohm tap is because of the JBL 4698Bs which Craig owned for a while: the woofers are 4-ohms. Necessity was the mother of invention. The SJR can be ordered with 2A3 tubes instead of 300B. Standard, the SJR comes with 300B and feedback. Those who prefer a bassier, thicker, and heftier sound a la Amp&Sound will want to order it without feedback. The SJR never gets quite as thick and rolled sounding as the Amp&Sound stuff with or without feedback. I like the transformer in that it doesn't have overblown mid or upper bass, but it packs a ton of punch just below the mid-bass and is full-bodied in the mids. This effect is exaggerated in the non-feedback version. The non-feedback version has quite a punch! The downsides are less controlled and articulate bass and slight high-end roll-off. It's a 300B after all and this is how 300Bs sound. The good thing is that the sound isn't soft. The AF 2A3 is a little softer and less punchy, feedback or non-feedback. The feedback version of the 300B is what I would recommend. This approach tones down the 300B sound and results in what I would like to say as "the best of the 300B without the worse of the 300B". The resultant sound is very stately, controlled, perfectly damped. In comparison, the mids and highs of the non-feedback AF 2A3 tended to be a bit jumpy and overly lively (this is more of a transformer issue than feedback issue). Nothing is for free of course. The feedback does constraint the soundstage and immediacy factor by a tiny bit, but with the 300B, I find that the positives outweigh the negatives - this keeping in mind that I am not exactly a 300B fan. I am uncertain if balanced inputs (iso transformers in the chassis) will be offered. I'll check the metal work next time I am in the lab.