* The correct loading for any cartridge will be such that it does not ring at audio frequencies- IOW if you run a squarewave through it, a squarewave will come out with no ringing.*
Ringing at audio frequencies might be a your criteria for loading an MP-1, but there are certainly other considerations for the rest of us, and I would think for MP-1 users as well. That is the sound, irrespective of RFI.
That bit about squarewaves is cute, but would leave a lot of people scratching their chin and changing load. I'm not saying your criteria is irrelevant, but it's not the ONLY criteria.
* With any LOMC cartridge ever made, this will be the case at 47K. So why do we hear differences? It has not so much to do with the cartridge and **everything** to do with the phono preamp. If the preamp is sensitive to Radio Frequency Interference, then loading the cartridge will affect tonality as it detunes the RF circuit formed thus*
Changing load does not necessarily affect tonality. The highest value or 47K is often not the most desirable. BTW, why stop at 47K, why not 1M or infinite?
Congratulations on the new cart.
You might find that dynamics and stage get larger with a higher value load, and focus more precise with a lower value.
Sloppy bass would suggest a lower load. It might take some experimentation.
*The answer has to do with how the phono stage reacts to RFI as I have pointed out.*
Loading encompasses more than RFI as I have pointed out.
*Designers also have to be pragmatic about what sort of input impedance is needed to control noise! If it were to be high as you ask about, controlling noise becomes a major problem in a high gain circuit! So 47K was derived as a reasonable compromise decades ago- it allows low noise and a moderate, easy load for almost any phono cartridge.*
1M doesn't seem to be much of a problem with Herron phono stage, but that's beside the point. 47K became a default standard for HO carts, not LO carts. For 4-ch it was 100K, but that's low gain. Look at vintage preamps and see what the loading options are.
*Regarding the sound, it cannot be considered 'irrespective of RFI': in plain and simple terms if the circuit has RFI problems **the sound will not be right if RFI is present!!** If such is the case then loading will have a beneficial effect.*
If a circuit does not have RFI problems then loading can still have a beneficial affect.
*The RFI is generated by the pickup and cable itself: it is not a matter of shielding from radio stations.*
Novel way of looking at a generator, or is it a transmitter? The oscillation or ringing occurs in the preamp because of the extraordinary amount of gain needed.
The tiny voltage of a LOMC still has inductance, which combines with cable and preamp capacitance and can cause HF ringing, but is only a problem with extremely low output carts with high resistance/inductance. I think such occurrences are beyond the bandwidth of your phono stages.
Saying RFI is generated by the cart is misleading. It is not. There are other loading considerations with MC's, none of which are about noise or tonality. You assume the higher the load, the better. I beg to differ. Such things as imaging, stage, dynamics, detail, and focus can all be affected by load, while tonality is unchanged.
Loading is very much about the cart and particular preamp.
I see you brought back up. The LOMC I was referring to are some of those coreless designs with very low output and high inductance/resistance relative to other MC. It was J Carr who told us about the HF oscillation/noise that could occur.
Regarding the notion that higher value loads are necessarily better, consider this:
If 500 ohms sounds good, and one tries 47K and it also sounds good but different, and both loads seem equally quiet, why is 47K better?
You're saying it is and you're wrong IMO.
A coil with a magnetic core is more efficient so air core coils must be larger to get a usable output. The newer AT air core designs are the exception, probably using stronger magnets. Older designs like the DL-S1 have very low output and relatively high impedance/inductance.
OP has a Black Box, not a Herron or MP-1, and I would guess that some of what you say about to the higher usable value, might be appropriate, but it's not a rule.
One of my solid state phonos' has a much higher S/N, and it's obvious your loading "rules" are not always correct.
*The larger you make an air coil, the lower its inductance.*
In this case larger means more turns - higher inductance.
*The noise that a phono section has is usually not a function of loading. There are a lot of factors that have to do with noise- it is an immense topic.*
Okay. By the same token loading preference is not always a function of noise, as you contend.
If the cart gets bright (change tonal qualities) with higher value load, it probably is as Atmasphere says. Not sure what good that knowledge will do. You'll load it down anyway.
I take it that changing loads in the MP1 isn't that easy. I was thinking, perhaps something like 10 or 20K might tighten up the bass without sacrificing that glorious sound.
This is the preamp you modified for additional gain? Output appears to be 0.05mV.
I think I remember Jcarr recommending the MC3000 which looks similar.
There should be no tonal change with different loads. If there is, it's either RFI or intermodulation from that high frequency oscillation. In such cases all you can do is load it down or try another cartridge or phono stage.
*If the cable capacitance is low, the resonance will be in the MHz region, in which case if the preamp does not care about RFI you simply won't hear a difference unless you load the cartridge so low that its output drops.*
If capacitance is low, and if preamp does not care about RFI, then you won't hear a difference with what, change of load, change capacitance?
What are you talking about?
If you're saying resistance load makes no difference in the absence of noise, you're wrong.
*That is why you can't have the same loading for all installations of the same cartridge.* (cable capacitance differences)
With RFI absent, why not?
Of course you can.
The correct loading for the cartridge is 47K ?
There is no "correct" loading. Assuming you're going straight in, why don't you start at 100 ohms as suggested by Shelter and adjust it to taste?