OTOH, do tubes have a distinct advantage?? I would say that they do when
it comes to overall SQ, plus the decreased likelihood of overload, BUT
they are never 100% quiet...at least IME. There is always some minimal
hiss..and this leads me to believe that their noise floor has to be
higher than ss.
Yes, they are noisier but they can be quiet enough that 0.2mV is no worries.
Jonathan Carr never says anything remotely similar about optimum
loading for his cartridges. I am looking at Jonathan Carr's loading
chart that came with my Etna as I type this and depending upon the gain
setting and the total capacitance of the tonearm wire in interaction
with the phono stage and the recommended loading ranges between 104 and
340 ohms for 0dB gain and between 284 and 887 in the highest gain column
of +6dB. @fsonicsmith
But that is Jonathan Carr who sees things (rightly so)
from the perspective of the cartridge manufacturer. Now lets talk about
phono stage producers. They don't espouse charts, they talk about
listening. Each phono stage manufacturer knows the attributes of their
designs. My Manley Steelhead with built in step-up transformers is not
going to behave the way a Sutherland 20-20 (just for example) will.
To say that 47K is the standard or de facto or even starting-point loading for a LOMC is ludicrous.
You might think it ludicrous, but 47K is the industry standard for phonograph inputs nonetheless. Because many phono sections have problems with the RFI generated by LOMC cartridges (keeping in mind how much gain they employ to work with cartridges of output this low) its common to see loading options on such preamps. Think about it this way: Since all cartridges are different, and you need an input resistance with any circuit that can amplify, what would be the correct value for that resistance?? You might ask your self why most phono sections have a 47K input impedance... the answer is that is the industry standard; it was not something that is a random coincidence that so many phono sections are built this way.
Jonathon has his recommendations for a very simple reason: He cannot be sure that the phono section to which you are connecting his product is going to be alright with the RFI generated by the cartridge/tonearm cable combination. Further, he's also go not idea what cable you're using! So he has loading recommendations on that account, and they cover a range rather than being a specific value. He also knows that most phono sections don't deal with the RFI issue very well. But if you talk to him, which I have done in person, you find out that he thinks 'no loading' (IOW the stock 47K input of the phono section) is better if you can pull it off.
Its true as you say that not all phono sections act the same :) That is a bit of an understatement! For example, a phono section employing an SUT will not have RFI issues, since the RFI is blocked by the SUT. Instead, you have to be careful to load the output of the SUT correctly so that the transformer does not 'ring' (distort) on account of the specific impedance of the cartridge (if you want to know more about how the ringing phenomena works please ask). So you'll find that depending on the cartridge, different resistor/capacitor values are used to accomplish that loading. So yeah, that's quite a bit different from a solid state phono section using opamps or an all-tube phono section that can run the LOMC cartridge straight in!
There is no single advantage, today SS phono stages just can't be
overloaded in normal condition: comes with very good headroom. That "
problem " was a " problem " of the past/several years ago.
With a solid state phono section using either opamps or discreet transistors, its the part that is outside the feedback loop that is open to overload. This is the input circuit of the preamp, which might be no more than the base of the input transistor. We're talking about an electrical peak of 20-30dB that occurs with all LOMC cartridges in tandem with the tonearm cable (the former having a high-Q inductance, the latter having a capacitance; the two in parallel form the resonant circuit, whose resonance might be at several MHz). While there are SS phono sections that deal with this properly (Pass Labs for example) its a falsehood to say that all of them do!
Its a simple fact that if the designer has not made provision for this resonant peak, it can overload the input circuit, resulting in a tick or pop when it does so. To get around this problem, you have two options: design the phono section to take quite a bit more input voltage than LOMC cartridges are known to produce (and do as much as you can to prevent RFI from coming in through the input connectors), or come up with a loading provision (the 'loading resistor'), so the resonant peak can be detuned.
Of course if you use the loading resistor option, you are asking the cartridge to do more work. If you're using 100 ohms as a loading resistor, that's a couple of orders of magnitude more work than if the cartridge is driving 47K. This results in the cantilever being stiffer- the same as what happens with a raw woofer if you short it out (they are both based on the same principle of operation). This is not a matter of debate, if you feel the desire to do so, take it up with Mr. Ohm. Ohm's Law cannot be defeated and isn't open to interpretation. If there is more current flowing, it has to come from somewhere and that somewhere is the motion of the stylus in the groove. So the fact that the cantilever gets stiffer is not controversial. Anyone versed in the art knows this- Jonathan Carr and I discussed this issue at the Munich Show a few years ago.
Raul's stipulation that this overload issue is something of the past is correct as most phono sections were only designed to have 'enough gain, low enough noise and proper EQ' and the electrical resonance was ignored. But he is incorrect in his assertion that this has been put to bed; this is why loading provisions exist on current equipment and are identified as 'loading' when they are really there for the benefit of the phono section, and the phono section will sound different if the RFI isn't suppressed. Its likely that the cartridge will sound different too, not because you are preventing it from ringing, but because the cantilever becomes stiffer as the 'load' resistance is decreased. This measurably affects its mechanical resonance in the tonearm.