Cartridge impedance loading question

Pkoegz, When you mess around with very low output cartridges, there are many sources of noise besides RFI. If you hear noise, a careful investigation is in order to try to reduce it or eliminate it, but in some cases, especially with an all-tube phono stage, you may just have to live with a faint background hiss. I find this not to be annoying, since it is really only apparent when the stylus is up off the LP or during silent passages between cuts on an LP. In the situation you describe, I would advise leave well enough alone. There is no reason at all to fuss with the cartridge loading, and moreover, the loading will have only an incidental effect if any on "noise".

I think you miss understood, I have no noise. I was just wondering if that ment I did not need any loading. Since posting I heard from the engineer/designer of phono and sut. He confirmed based on the cartridge I was using, he would not "use any additional loading". I am a happy😺

And a cool cat, too.

Pkoegz, its a good idea to try the loading at least. If it improves the sound (reduces brightness without affecting speed or bandwidth) then it tells you that despite low noise, the preamp is sensitive to Radio Frequency Interference (RFI).

This interference is generated by the pickup itself, as explained previously. If you hear little or no difference, then its no worries- the designer of the preamp has done his homework.

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

In the old days before digital computers automotive companies use to model their suspension designs with analog circuits using inductors, capacitors and resistors. In the spring/mass system energy sloshes back and forth between the kinetic energy of the moving mass and the potential energy of the spring. In the electrical analog energy sloshes back and forth between the electric field in the capacitor and the magnetic field of the inductor. In the mechanical system the resonance is damped with a shock absorber, in the electrical circuit the resonance is damped with a resistor. Both systems are governed by the same differential equations. So the analogy is very apt.

The fact of the matter is a cartridge has inductance and forms a resonance tank in combination with the input and cable capacitance. The resonance peak will occur at a very high frequency, well beyond the audio band. Depending on the Q of the resonance you will see a rising frequency response well down in frequency from the peak. The Q of a resonance is determined by the source resistance of the cartridge and any load resistance. Now I will readily admit that if your phono pre is susceptible to RFI and your cart. is undamped, RFI will excite this resonance and raise all hell. That said, if your phono pre is not susceptible to RFI the resonance will still be there and the rising high end response it causes.

MC cartridges also have mechanical resonances that with some cart. need to be damped with a load resistor. Think speaker resonances and a low source impedance (high damping factor) amplifier.

But look, if you like the sound of your cart. running it wide open then go for it. Just don't make some kind of religion out of it.