Question about Cartridge Loading

My Pure Fidelity Stratos (based on the Gold Note Donatello) has a 45 ohm impedance and recommends loading between 400-500 ohm (figuring 450 ohm to be optimal?). However I haven’t really heard any difference between 100 ohm and any variation between 400-500 ohm. 

What I did on my JC3+ phono stage was set the variable dials to 450 ohm and then flipped the switches between MC Variable and MC 47K and that’s where I actually noticed an improvement. At 47K the soundstage is wider and deeper with no detrimental effects that I can hear on top end, harshness, or bass, so that is what I’m sticking with. 

I am guessing a lot of this must be system-dependent because according to the manufacturer I should get optimal sound between 400-500 ohm but according to my ears I can’t hear any differences or improvements until I load it all the way at 47K. 

It's not that 450 ohms is "optimal".  It's that you want the phono stage input impedance to be at least 10X the internal impedance of the cartridge.  In your case, 10X = 450 ohms.  So any input impedance equal to OR GREATER THAN 450 ohms would comply with the conventional wisdom.  If you don't hear a difference between 100R and 450R, I suggest you try 1000R or even 47K.  Also, check the VTA for your cartridge.  If the tonearm is not level with the LP surface, is the pivot lower than the headshell?  That can cause loss of HF response.  Also check for any number of other things that can affect HF response.

Dear @lewm  : The OP cartridge was reviewed and the reviewer said performs just fine at 100 ohms that's is way out of your 10X rule. In reality it's not a rule because I experienced several cartridges below that with very good listen sessions.  

Btw, "  does it really matter much to include inductance in the calculation?  I doubt it. "  Do you already make your job using Hagermann calculator at least with 6-7 different examples?  if not then maybe time for you can do it and confirm that " doubt " you are talking about. Don't you think?

R.

Raul, It’s not my rule. It’s just physics. If you load a cartridge that has a 45R internal impedance with a 100R resistor, of course it will work. But a large fraction of the cartridge voltage output will be lost to ground and you will lose some HF bandwidth. These two numbers can be precisely calculated but the end result is more complex because of frequency dependency. If the net result sounds best, I am not about to quibble, but if a novice asks me a question about loading, I feel obliged to tell it like it is. Then let the other guy decide for himself.

As to the importance of inductance in the Hegerman calculator for LOMC cartridges.  Did you add in say 10-20 microHenries for an LOMC, or whatever is the value for any particular LOMC?  And does it make a difference?  Of course it will perturb the value a bit, but not by any important amount.  Tell me what you found out.

Jay, I always use the cartridge manufacturer's suggestion and stick with it but, my phono stage requires removing the bottom and soldering in resistors to change the load. Just use what you think sounds best to you. It is your system and your ears. 

With experience you will know what you want to hear. When you are not sure you tend to second guess yourself. As an audiophile you owe it to yourself to listen to as many systems as you can at dealers and shows to get an idea of what systems can do. You'll have to dweedle through a bunch of bad systems but when you hear a good one you will know it for sure. If you want to get first rate service at a high end store just drive up in a 911. A Yellow one works best:-)