Cartridge impedance loading question

The MP-1 has loading strips mounted on the rear panel by the phono input. It might be one of the easier preamps to set cartridge loading.

Atmasphere is of course correct re the ease with which the load R can be changed on the MP1. I, however, never happy unless I am messing around, have installed a 4-pole, DT switch on the rear panel, such that I can choose among 3 load resistances without having to gain access to the rear of the preamplifier to change resistors, as is needed with the OEM set-up. With my switch in neutral position, the load is the basic 47K. With the switch in either of the other two (up or down) positions, the load is 100R or 1000R, respectively. Of course, both those values are in parallel with 47K, so the actual R is slightly lower than either 100R or 1000R. Should I feel the need, it is no problem to modify this arrangement. Truthfully, I am not at all sure that the flabby extreme low bass response I hear with the 47K load is per se due to effects of that load. It could be a tonearm/cartridge resonance thing. Anyway, it's really not objectionable compared to the other benefits.

Interesting: The URL offered by Atmasphere gives access to calculators for both RC and RL type filters. Using the RC calculator, I cranked in 150pF as an approximation of capacitance of my tonearm wire plus that of the phono input stage (which is a cascode and thus not sensitive to Miller capacitance, anyway). The equation itself tells you right away that fc is inversely related to both R and C; thus it is no surprise that when R = 100 ohms, fc is >10,000,000Hz. When R = 47K, fc comes down to ~22,000Hz. So if you look at it as an RC circuit, 47K would not make for a bright sound, compared to 100R. I then cranked the same values into the RL formula, were fc is directly proportional to R. I used 50 microHenries as an approximation of the inductance of the MC2000 (a typical value for a LOMC cartridge). Not surprisingly, in this case, when R = 47K, fc is much higher than when R = 100 ohms, but even with 100 ohms, fc is >300,000Hz. So again, 47K is not going to make for a brighter sound that we could possibly hear. In the actual situation, fc is a function of R, L, and C. Comments of Atma and Fleib, or anyone else, appreciated.

Running a typical MC cart. with a load of 47K is kind of like driving your car without shock absorbers. The inductance of the cart. in combination with the load capacitance forms a resonance circuit. With a 47K load and typical values for inductance and capacitance the peak is usually well past the audio band. The audio band may still be flat, but he response above the audio band will be rising. This will make the system more sensitive to surface noise and pops and other ultrasonic disturbances. If rise intrudes into the upper audio band any excitation of the resonance (ultrasonic surface noise and pops) will be made more audible.

Load the cart. down with a too small value resistor and the frequency response starts to drop in the audio band. Get it right and the response will be maximally flat. Load it with a high value resistor and get an ultrasonic peak in the response.

John, Please see my post above and Atmasphere's post above that. The numbers say that what you say is happening in the audible band is happening at way way higher frequencies than that. Can you offer the math? Aside from that argument, if you listened to an MC cartridge loaded at 47K, and if it sounded better in most ways at 47K than it did at some significantly lower value (higher load), would you then conclude that you had to change the load resistor to conform better to the theory, or would you say f*** it and just enjoy the music?

Then too, we have the arguments from Jonathan Carr, Allen Wright, and Ralph Karsten, not to mention other authorities we do not know about, all to the contrary of your position. I concede that all of those guys, as well as you, know more about the physics of the situation than I do, but there is an argument opposite yours, apparently.

These analogies between cartridge loading and automobile technology have their limitations.