Cartridge impedance loading question

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.

I suppose if you were to use a transformer placed close to your TT to keep leads very short you could push the resonance up past 1mHz. In a more normal situation I would guess it would be hard to push cable and input capacitance much below 100pF. Without an input transformer the input stage would have to be probably a cascode for the high gain needed without getting killed by the Miller effect.

A cartridge with 5mH inductance in combination with 100pF has a resonance of 225kHz. A typical system may have more like 200pF. This results in a resonance of 160kHz. A sharp impulse like from a scratch will generate a lot of high frequency harmonics and could conceivably excite the resonance and cause it to ring generating bursts of high frequency noise. Now as long as your phono pre is hunky dory dealing with bursts of high frequency signal (no IM with audio signal, or maybe it shunts these signals to ground with a ceramic disc cap at the input?) you're good. The 75uS time constant will roll this stuff off, usually after the input stage. In the above examples the resonance is 6 to 7 octaves above 2.122kHz so the ringing will be attenuated by 36dB - 42dB (unless your phono stage uses the 4th pole and shelves the response at 50kH). Not gone by any means. Could still pollute gear downstream. That said, there is enough going on that in the end one's own ear should be the final arbiter.

Some might find the thread below interesting.

thread