Cartridge loading

What I experienced always is that at 100 ohms quality level cartridge performance is always better

If your phono section has RFI sensitivity what you state above will be the case as I’ve maintained also on these threads.


With regards to the load impedance affecting the cartridge, of course this happens. Moving coil cartridges work on the same principle as a loudspeaker; now think about a kid’s walkie-talkie that has the speaker also double as a microphone. In other words, the speaker can be driven by energy or it can make energy, because it is a **transducer**, and with any transducer motion is converted to electrical energy and vice-versa.


You can test this easily enough- remove the grill from your speaker and see how easy it is to move the woofer if nothing is attached to the speaker terminals. Then short out the speaker terminals and see how easy the woofer is to move then! With a cartridge its no different- the more you load it down (lower resistance loading resistor) the more work it will have to do and so the cantilever will be harder to move. Since this is also the idea of ’damping’ we can easily infer that mechanical damping of the cartridge will occur if the load impedance is reduced.


Anyone schooled in the electrical arts will understand this immediately; and thus also that high frequency output of the cartridge will be reduced as the cantilever is made to do more work. If this is not readily apparently please do more study of electrical theory.


Now there is one exception with regards to the input impedance of the phono circuit- the load impedance must be connected to the cartridge in such a way that it causes it to do more *work*. If the cartridge is not doing any work then it will be unaffected. Now refer to the article at this link previously given:
http://phonoclone.com/diy-pho4.html

We can see that the cartridge is actually being loaded by the input of the opamp; which if measured will be found to be quite high (most modern opamps are FET input). The idea is to replace the input resistor with the cartridge itself- so that the virtual ground (present in any opamp circuit) is the output of the cartridge itself. In this circuit the cartridge isn’t doing the sort of work as it would be if the cartridge were presented with an actual 0 ohms impedance!! IOW, zero ohms and *virtual ground* are not exactly the same thing! I refer you to OPAMP theory 101 as to why. As a hint, the closer the gain of the opamp is in open loop to infinity, the more the virtual ground will behave as it it is zero ohms **as far as the opamp is concerned**. This is more of a control theory thing which is far more text than I have time to put here, especially since you’ll need an EE degree to follow along. Just take it for now that a virtual ground isn’t the same thing as actual ground or zero ohms! If it were, no amplification could occur!

@lewm

Is THIS what you have?https://audiocubes.com/products/47-laboratory-4712-phonocube

Yes, it doesn’t work without special power supply, so there must be a power humpty (first in the list) and i have it with my phonocube.

If you’re buyin’ a Phonocube without power supply it looks like a good deal, but it doesn’t work. The power supply is 3 times bigger than the cube itself and superheavy. For superb results some people use 2 power supplies for 1 Phonocube (dual mono).

More images of this set with power supply and cube are all HERE (not mine).

And you can study about parts and its unique but very simple circuit HERE.
Let me know what you think now when that guy cracked it and explained why the input impedance is almost ZERO. But that guy is not the designer of the Phonocube, he just made a clone.

P.S. I think i posted all these in another thread long time ago.
The PhonoCube originally designed for Miyabi 47 Lab cartridge. 

Which current injection phono stage do you use ?

Let me know what you think now when that guy cracked it and explained why the input impedance is almost ZERO

@chakster This statement isn't correct. The **virtual ground** is almost zero, not the actual input impedance. Its a bit tricky explaining what the difference is but put it this way, if you turn the unit off you'll find that the actual input impedance is quite high. Apparently it has a pretty good opamp, since that is required in order for the virtual ground to approach zero.

The idea is to replace the input resistor with the cartridge itself- so that the virtual ground (present in any opamp circuit) is the output of the cartridge itself. In this circuit the cartridge isn’t doing the sort of work as it would be if the cartridge were presented with an actual 0 ohms impedance!!

Very interesting @atmasphere  
I wish i could understand more, they don't make Phonocube any longer, probably because they do not make Miyabi 47 cartridge anymore.  

Any other phono stages with the same circuit ? 

Dear @atmasphere  : Your post is not an answer to what I asked to you:


"""   how did you measure that " limit trace " as a function of loading and which is the point/value where the loading figure starts to " limit trace " abilities in the cartridge?  """

that is what needs a more specific answers because you posted here and in several other ocasions:

  """ will limit the ability of the cartridge to trace higher frequencies .."""


 Lewm my answer to you is that other than " science " we have to use common sense and here what I posted before to you:

"" did you know how much " force " do you need to apply/need/ at the base of the cantilever to really impedes at the stylus tip position its free movements, a tiny movement? no? 
Btw, do you know the " power forces/inertia " generated at the stylus tip when ridding the grooves at 33/45 rpm and what " force " is need it to " limit the trace " of the stylus tip to track when appliyed that force/loading at the other end of the cantilever? ..."""

Which is the force need it to broke that very high inertia generated by the friction between the groove modulations and stylus tip when the cartridge is ridding/tracking those grooves that can " limit trace HF "" ?

I don't know that answer concerning the loading resistor value to broke that inertia. We have to think that load resistance takes its effect at the cantilever base and the stylus tip is ridding at the other end/extreme of the cantilever and this makes " things " extremely complicated to that " limit trace " issue.

That theorical electrical loading effect is converted in mechanical energy ( the " force ". atmasphere said: stiffer the cantilever. ) what makes it even more complex due that in the mechanical land we have to take in count several parameters as: compliance of the cartridge, cantilever length and overall dimension and characteristics, status of the stylus tip because if the cartridge has over 1.5 khours of use its own tracking abilities changed that when the stylus had only 300 hours and not only that but even its compliance through more playing hours could changes too, the stylus tip inertia is different depending its position in the overall LP grooves and other parameter to take in count is the different velocities recorded through the LP grooves surface, etc, etc.

So, till now exist no true evidence that that " limit trace..." can happens.

@atmasphere can you answer the original questions?

R.