Why does impedence matching matter for phono signals?

[rattlesnake]

I'll start with a question about impedence in a phono cartridge. If a mm cartridge is rated at 47,000 Ohms, is that the same as the unit's "output impedence," and is that also the impedence of the coils in the unit that generate the audio signal? Please correct me if any of this is wrong.

Given all this, why does it matter for a phono cartridge to have a similar impedence to the imput impedence of the phono preamp?

 

[sergeauckland]

There's no impedance matching for a phono cartridge, MM or MC. The input impedance is some 5-10x the output impedance of the cartridge.

Most MM cartridges are designed for an impedance of 47k, which is therefore what most phono stages provide.

If one wants to optimise an MM cartridge, then one needs to adjust both the capacitance and resistance, but that's unusual on many phono stages, if there's any adjustment provided it's capacitance only.

MC cartridges have the advantage of being pretty immune to loading, as long as it's 5-10x the coil resistance.

S

 

[AnalogSteph]

MM cartridges are severely inductive sources - imagine 750 ohms in series with 400 mH or so - and as such are quite touchy when it comes to load impedance (resistance and parallel capacitance), as impedance rises into the tens of kOhms in the treble region. The resulting overshoot in the response (RLC circuit) is commonly used to prop up the treble response which often is naturally drooping due to increasing losses.

 

[JP]

MC cartridges have the advantage of being pretty immune to loading, as long as it's 5-10x the coil resistance.

Even 1:1 or worse an LOMC is rather immune aside from output level.