Oliver Archut designed a mic pre with two ranges of variable impedance, his TAB Funkenwerk V77M. According to the product literature, ribbon mics can be quite variable in their output impedances, and this pre is designed to accurately match impedance on a mic-by-mic basis. I do not have this preamp, though I do have the V78M. It is pretty good. Since Oliver's passing, product availability from AMI seems uncertain. The AMI website has not been updated in years. They do answer email. Inquiries have been answered with the hope of availability in the future. It does not seem we are there yet.