Cartridge impedance loading question

"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.

John, I won't make a "religion" out of it, if you won't say I was making a religion out of it. The hostility in your response is inappropriate. I only relayed my preliminary and to me surprising observations; I did not say anywhere that I had found a new God or even that everyone in the world should use 47K as an MC load. A priori, I thought the same as you, and I probably don't even disagree with you now. I thought it was an interesting topic for discussion and that this thread was proper for discussing it.

As pointed out, the capacitance of the interconnect cable has a big influence and may actually be more important than the cartridge. That is why you can't have the same loading for all installations of the same cartridge.

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.

Atmasphere,
*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.
Regards,

Capacitive loading will make a difference- its the same as using a more capacitive cable, which is to say its probably something you want to avoid as it will lower the resonant frequency of the RF circuit.

A capacitor can be quite useful in loading MM cartridges however, but this thread so far has been about LOMC cartridges.

If you're saying resistance load makes no difference in the absence of noise, you're wrong.

Pretty sure I didn't say anything like that. But to address the comment, loading can indeed affect noise because if the preamp is susceptible to RFI, eliminating the RFI very frequently will reduce noise it can cause.

Again, if you find that loading is improving your noise floor, its likely that your preamp has problems with RFI.

And not to repeat myself too much but also again, if the load is too severe (too low a value) it can have the effect of degrading your noise floor on account of the fact that it is reducing the output from the cartridge.

Now this means that loading can be a bit tricky if the preamp has RFI problems because it is not predictable what the right loading value will be on account of the interconnect cable. Things become a lot easier when the preamp resists RFI- then all you do is keep the cable capacitance down and life is good.