@chakster Many thanks for you detailed reply. I have completely misrepresented, and severely underestimated your extensive collections of MM and MC. The MC list you posted will be a guide to me. Though I am curious, there are a few in the list, EMT in particular, with internal impedance in the teens, I think there is another in the twenty’s range. They work with the 47 Labs unit?
Since it was recommended for low impedance cartridge I use it only with low impedance cartridges (under 5 Ohm) and it's excellent. At the moment my FR-7f cartridge (on FR-66fx tonearm) connected to 47 Labs Phono Cube and the sound is wonderful.
I use genuine 47 Labs Phono Cube with Power Humpty. Not interested in clones of whatever products in audio, in case with 47 Labs products I really like the aesthetics, those units are state of the art design in my opinion. Someone posted a links to high quality pictures of the 47Labs PhonoCube and PowerHumpty. Beautiful gear!
Regarding the clone (and its circuit) read this.