well, i've not heard the Atma-sphere MP-1 so I cannot comment on its sonics; someday I will hear that preamp....
As far as the CAT preamp goes, I've owned a SL-1 Sig Mk3 for many years & at present I own a SL-1 Renaissance. Both preamps, IMHO, are stellar as they give you the music straight-up without beating around the bush. I used Tele 12AX7s in the line-stage & Amperex 7308 in the line stage as well. In the phono stage I use the factory supplied tubes as I do not think that I can do better. NOS is not an option - too noisy & stupid-expensive for ultra quiet NOS tubes.
As for tube rolling, I always ran NOS, mostly Tele's, but the forward, aggressive character remained.
this does not sound right. In all the years of listening to the CAT sonics, I cannot call the presentation forward nor aggressive. you *must* have had some other distortion in your system that the MP-1 smoothed out.
JWM and Charles are exactly right, as much as I liked all my CATs, every one of them came across sounding a bit lean and cool. When pushed, the sound became hard and aggressive.
once again, something does not sound right. you must have had some other distortion in your system that you remain unaware of.
No way the MP-1 is "diffuse and colored". What nonsense!
well, you guys are trading punches so do respect the other fellows opinion. It's not diffuse or coloured to you but it is to him; the CAT is aggresive, cool & forward to you. Each of you has an opinion; I'd say it's par for the course....
But... none of them can be compared to a good VAC or a fairly recent MP-1.
I cannot comment on the MP-1 but I've heard some VAC units at a friend's house (I cannot recall the exact model name) & at shows. Plus, I have the opinion of my friend who used to work for VAC some time back designing circuits for amps & preamps - I respect this person's opinion highly. As you know, You cannot make judgements on gear at shows as the environment is so out-of-control but I can easily say (from my in-home listening experience) that VAC sonics do not come close to the CAT sonics. The VAC sonics, in my mind, are definitely more coloured. If that suits your tastes, well & good.
well, I think all of us have laid out our respective opinions (& more!). hopefully this is enough info for the OP to make his short-list. It does not matter to me what he selects finally - CAT or VAC or J-E or something else. In the end, he has to enjoy his own system that he needs to build for his tastes. If we like what he builds that's just a bonus for the OP.....