@vpi: Basically the hum level is strongly related to the efficiency of the magnetic circuit and specially the coil wire diameter.
Increasing the number of turns (because of an air coil or more windings for a higher output) basically means thinner wire.
Thinner wire helps to increase the signal, but even more increases coil resistance (ca. = impedance at audio frequencies). This leads to higher hum susceptibility with unshielded wiring.
Air bearing arms need at least 15cm of unshielded wires for the wiring loom. This increases the minimal level of hum.
With luck and good systematic grounding of arm and any conducting surfaces around the arm / platter / plinth / motor, and shielding the signal cables, grounding them independently at a single point at the preamp/step up input should eliminate any problematic level of hum.
My experience with the ET2 is that it’s unproblematic with low impedance MCs, even with unscreened cables, which I prefer.
In my actual situation with a London cartridge the source impedance of the coils forces me to implement screening – which is what I am working on this weekend...;-)
Increasing the number of turns (because of an air coil or more windings for a higher output) basically means thinner wire.
Thinner wire helps to increase the signal, but even more increases coil resistance (ca. = impedance at audio frequencies). This leads to higher hum susceptibility with unshielded wiring.
Air bearing arms need at least 15cm of unshielded wires for the wiring loom. This increases the minimal level of hum.
With luck and good systematic grounding of arm and any conducting surfaces around the arm / platter / plinth / motor, and shielding the signal cables, grounding them independently at a single point at the preamp/step up input should eliminate any problematic level of hum.
My experience with the ET2 is that it’s unproblematic with low impedance MCs, even with unscreened cables, which I prefer.
In my actual situation with a London cartridge the source impedance of the coils forces me to implement screening – which is what I am working on this weekend...;-)