Cartridge Loading for a phono pre amp

I was the one who wrote previously about Faraday's Law and Lenz's law in support of Carr's assertion.

For your information, I have designed DIY phono stages that embody the characteristics that he espouses- very high supersonic overload characteristics for example- and are extremely compliant to the RIAA characteristic, very low noise, and essentially unmeasurably low distortion. There are several hundred of them out there...

In any case, there are no conservation of energy issues here. The mechanical energy of the groove wall reaction to the gravity induced downforce (i.e. the forced motion of the stylus) "uses" Faraday's law to produce an output EMF (voltage). That voltage produces a current that complies with Lenz's law- which essentially defines the inductance of the coil and occurs as an energy conservation consequence- and that current is defined by the total impedance of the coil- the inductance, the capacitance and resistance- the equivalent load impedance in fact.

The back emf is just due to the inductance, and is proportional to the frequency.

For a 10uH inductance at 20kHz, the impedance is about 1.6ohms, so relative to a 100 ohm R the back emf generated that opposes the input voltage is about 1.6/100 of the input voltage, and 90degrees out of phase, so it's about 0.1dB of the signal amplitude.

Yes, the back emf opposes the motion of the cartridge, but it's very small compared to the generated voltage- which is due to the conversion of mechanical energy to electrical energy as described above- and essentially can be ignored in calculating the dynamics of the cartridge arm system.

Just another bit of food for thought.

Say that the effect of back emf is in fact a change (increase) in the effective stiffness of the cantilever assembly. Does that matter? Is a higher stiffness a good or a bad thing?

Equivalent circuit of a phono cartridge (pspatialaudio.com)

In the above you can read that it's really just a "thing" not necessarily good or bad, and small changes are of minimal consequences.

You will also discover that many of the things that you thought you knew about cantilever design (i.e. Boron or ruby is better than Al) is not necessarily correct.

For reference, my favorite cartridge is the Miyjama Madake and it has a composite cantilever consisting of a tapered, hollow Al tube with the mounted diamond tip attached to a bamboo section. It actually lends itself well to the splitting of the compliance regions that the above analysis uses.