Matching the cartridge to the phono stage

The Hana SL has been on my table for the past two years, running into a Parasound JC3 Jr. (which allows me to adjust MC load using a variable pot that runs from 50-550 ohms). I can say that the differences in load between 100-400 are subtle, but there is a more pronounced treble "edge" and a more brittle sound on certain vinyl when running below 300 ohms. This is likely due to a drop out of the upper mids below that 300 ohm load.

@mrmojo 

The loading has nothing to do with the cartridge sounding different and everything to do with the phono section making less distortion. Also, a lower resistance might load the cartridge so much that the cantilever becomes so stiff it might have difficulty responding to higher frequencies.

The reason this is so has to do with the inductance of the cartridge. Its quite low! In fact its so low that if you pass a 10KHz squarewave through it (put the cartridge in series with the squarewave) you'll see on an oscilloscope that the output looks just like the input- no rolloff at all!

So the change in tonality is something else. There are two things to affect that. One is that the inductance is in parallel with the tonearm cable and its capacitance. That sets up an electrical resonance that is probably at 1 or 2MHz. That resonant peak is likely about 25dB (based on the Q of the inductance of the cartridge); when energized by the cartridge tracking an LP the resulting RFI can easily overload many phono sections, resulting in distortion which is perceived as brightness.

The loading resistor detunes the resonance. Brightness is gone.

But a 100 Ohm loading resistor is going to force the cartridge to do 2 orders of magnitude more work as opposed to the stock industry standard of 47KOhms. So the cantilever will be stiffer just as an alternator shaft gets harder to turn when its loaded. A cartridge is a kind of alternator. The decreased compliance can result in less high frequency energy and may affect how the cartridge tracks in the tonearm.

If the preamp is designed to deal with the RFI generated, you'll find that the loading resistor makes far less difference! When the phono section has a loading resistor switch, its a pretty good sign that the designer did not take the implication of an inductance in parallel with a capacitance (electronics 101, 1st week) into account.

To be fair, don't you think that a load resistance switch is sometimes a response to the marketplace which tends to place a high value on fiddling with load resistance, because most audiophiles, who are also potential buyers, do not understand the problem as you state it?  Whew! That was a long question.  Thanks.

@atmasphere 

Thanks for the detailed view of the interaction between cart and phono pre, very illuminating. I appreciate you sharing the knowledge. 

As for your last point about how the preamp design deals with the RFI, isn't some level of variability in load resistance needed? The market for MC carts presents a lot of options, all of which have very different specs. Or am I not understanding your point?

So much cool information here, I learned a ton. Thanks everyone. I think what I'm going to do is find a cartridge that fits my phono stage in the Luxman. I saw some people mention a match of Dynavector cartiridges, Benz, soundsmith. Some of them are expensive and I'm looking to find one for under 1K that sounds awesome. Maybe even Hana SH which matches better to the Luxman. I'm not going to do any modifications to the amp for sure, if I decide to do that then I'll just buy a separate phono stage instead. 

What about Fixed Coil Carts ? Do you guys have experience with those versus Moving Coil ? 

https://www.sound-smith.com/articles/fixed-coil-vs-moving-coil-why-make-jump-different-technology