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.

@wynpalmer4

👍 Thanks! It's always a pleasure to read your posting in here, AK and diyaudio!🙏

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.

Dear @wynpalmer4  :  Thank's to came to post here because y pasted what you posted several years ago in the subject that the " stifness in cantrilever " could have effects on HF tracking in the cartridge due to loading.

Here imhifiman and me made direct tests in our own systems with the same cartridges and after made changes in cartridge loading we detected no single difference exactly as you posted years ago about your Madake.

By coincidence and after all your evidence after all those years the same person, as in this thread, followed posting what he can't prove in any way.

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

Dear friends : For some of you that read for the first time the Wyn posts here next I paste what he posted several years ago in other cartridge loading thread:

"" No, I did not design the AD797. That was Scott Wurcer- a colleague at ADI and, incidentally, for whatever it’s worth, also an ADI design fellow. However, I know the design quite well.
He and I were colleagues in the opamp group in the 80s. He focused on high performance relatively low frequency opamps such as the AD712 and then the AD797, amongst others.
I focused on high performance high speed amps like the AD843, 845 (at one point an audio darling), 846 (also a transimpedance design with some very interesting design aspects that I gave an ISSCC paper on) etc. etc. mostly using a complementary bipolar process that I helped develop that I believe was also used in the AD797. I also did things like designing the FET based AD736/737 RMS-DC converter and others.
I moved on to more RF, disk drive read/write, GSM, CDMA etc. transceivers, signal processing, PLL and DSP designs. ""

and here somerthing that he forgot to mention and that comes in that " old " thread that shows that that " myth " of tracking problems due to cartridge loading changes is a lie and nothing more:

""" heavy resistive loading you state could be definitively true- certainly not on tracking which is demonstrably false based on IM tests on tracking performance that I have incidentally performed as a function of load. While mechanical impact does occur as a result of electrical load- there is some back emf necessarily generated by the signal current that affects the mechanical motion, but a quick back of the envelope calculation using Lenz’s law and the 10uH cartridge suggests a 2 orders of magnitude difference between the generated signal and the back EMF for a 100 ohm load at 20kHz- certainly not enough to cause tracking issues. """

R.