That's definitely not normal response for an AT150MLX, Technics SL1210, and Cambridge 640P (I have that exact chain and used it to feed line level inputs of an integrated amp as well.)
Follow Raul's and Mofimadness's advice and if those don't fix it, I guess you need to see if it's defective, given that your 440MLa worked fine.
Follow Raul's and Mofimadness's advice and if those don't fix it, I guess you need to see if it's defective, given that your 440MLa worked fine.