I've owned an SD30 for about a year. Excellent, incredible amp. I would have been perfectly happy with that amp for years and years...until I talked to someone and they said that the SD45 had those few little things that I was missing in the SD30: a bit more open sounding and a bit more upper end mids (less dark). Well, it appears that they were right. The Sd45 is a bit heavier but its still very light compared to most heads. Thats one of the great things about the Budda's: aluminum chassis. It came with Groove Tube KT66's and Sovtek preamp tubes. THe rectifier is a no name chinese. (Note: I put a GT rectifier in my Sd30 to replace the EH rectifier and it DID make a nice difference!). Soundwise it is definitely LOUD! Louder then the SD30 by quite a bit. I actually prefer the 30 watt power of the 30 better as I could turn it up a bit more to get the tubes to work a bit harder. The overall sound on the 45 is a bit more open and airy and less "jangly and chimey" on the clean than the SD30. It really is more old school Marshall sounding than the SD30. The drive channel supposedly has a bit more gain on tap than the SD30 but its a different kind of gain... The 30 is relatively dark sounding while the 45 is brighter. The 30 howerver retains that "creamyness" that alot of players really like while the 45 is a bit more "in your face" with the upper end mids. Long story short...both are incredible, incredible amps. Gigging tonight with both so I'll have a bit more info after tonight. Can only keep one..but am leaning towards the 45 right now.