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Hi I really need help here. I just bought a Shelter 501 MK3 installed on a VPI Classic 2 before I had a Sumiko Evo Blue Special My concern is the I have a Mark Levinson No. 25S Phono with separate PS but is the MM version therefore do not work well with the Shelter. I have 2 options Buy a step-up transformer like the Bob Devices Sky 20 or sell the Mark levinson and get a MC Phono Stage like the Manley Chinok I have no idea what will be the best way to go the ML 25s is amazing I also dont know how much to ask for it if I sell it. Please I need some input. Thanks.
If you like the ML, then keep it. Better the devil you know than the devil you don't.

The transformer will not change the basic character of the phono stage so you should be good to go.
That SUT is supposed to be excellent. Certainly the Bob's is a low risk option to try. He may even offer a trial w/ money back guarantee.
I would keep the ML and buy JC1 maybe the DC version....
I have not heard anything better than a Herron VTPH-2. I have heard from others that it brings out the best qualities of Shelter carts.

Do you think the ML 25S is the weak link in your system? The quality of your system can only be as good as the 25S.

You make the call.
Buy the Manley or other quality tube phono, there are other sonic advantages
that a tube phono pre has over ss.
Unless you can try it in your system, and so determine that it is an improvement, I would not buy a different phono stage at this point.

You like your ML phono preamp, so if I were you, I would buy a SUT from Bob's Devices. Per their website: "Returns are allowed within 2-3 weeks for full refund for any reason, less shipping costs, if returned in “new” condition."

If the SUT does not work for you just return it. Then you can search for a suitable phono preamp if necessary.

Call or e-mail Bob's Devices and they will help you determine the best SUT to use for your cartridge and ML phono preamp.
Thanks for all the replies it really help me, one question out of curiosity, If I later decide to sell my ML how much should I ask for it I have no Idea since is over 15yo but in near mint condition, thanks in advance!
Per the A'gon Bluebook ML No 26 phono Av. Resale $2,420.75