Difference in Inductance - How does it affect MM Cartridge sound?


Inductance of MM cartridges plays a role in their sound signature. Obviously i'm not attesting anything new or revelatory.

Not sure i understand exactly how it affects performance but was pretty surprised to find out how much different the same stylus sounded on cartridge bodies with different inductance (otherwise identical).

The two cartridge bodies belong to the same family, with interchangeable styli.

One is a Shure M55E (pre-2000, Mexico made) and the other is a Shure M44-7 (post-2000, Mexico made). Used the same stylus on both for evaluation (N55E Improved, original stylus). Cartridge headshell used, turntable, VTF and all the other variables were kept identical.

According to my LCR meter, the cartridges showed the following values:

Shure M44-7
Resistance: R 681Ω, L 680Ω
Inductance: R 568mH, L 606mH

Shure M55E
Resistance: R 690Ω, L 690Ω
Inductance: R 759mH, L 721mH

Didn't expect them to sound as different as they did, given the above values.

Resistance is almost identical, being only 9Ω and 10Ω higher on M55E, for each channel respectively.

Differences in inductance are more pronounced though. 191mH and 115mH higher on the M55E, for each channel respectively.

Links to audio recordings of both cartridge bodies with same stylus:
Shure M44-7
Shure M55E

When i listen the two recordings, the one with the higher inductance (M55E) sounds substantially wider in terms of channel separation and with less pronounced high octaves. The other body (M44-7), has an overall brighter rendition with a somewhat collapsed soundstage in comparison.

So, is it down to the difference in inductance?

My only reservation is that there might be other factors affecting the result, which i'm unable to identify/measure.

Regards, Nikos.
So, is it down to the difference in inductance?

You probably know more about the electrical characteristics of MM cartridges than I, but I'll start the ball rolling in your thread!

The MM cartridge is essentially a simple resistor, inductor, capacitor (RLC) filter which has a resonant frequency.

As the value of inductance increases, the resonant frequency falls, which would account for why the M55E has less pronounced higher octaves.

With a higher inductance, the electrical resonance will occur at a lower frequency and the response will fall off sharply above that frequency.
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I used to have a Shure M44/7. Good little cheapie. About 2g tracking weight and tough as old boots. The M55E must be a better elliptical stylus. Possibly tracks lighter.

It's tonally down to the interaction between cartridge inductance,usually 500mH, cable and preamp input capacitance (100-400pF) and the resistive preamp load which is usually 47k.

MM Capacitance.png


My experience is the lower the capacitance, the better it sounds. This, I think, is because the electrical resonance affects the mechanical properties of the stylus in the groove at the very highest frequencies.

A sort of mistracking.

If you add a couple of 1k metal oxide resistors in the cartridge headshell on the hot output's solder tags the sound is transformed much smoother, at the loss of a bit of HF and additional noise.

People argue about this endlessly, but I did a lot of experiments on this. My conclusion is some low inductance MI types sound much better. Grado make cartridges (say 100mH) like that. But need a heavy toenarm.
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