Moving Magnet vs. Moving Iron

The internet is full of discussions comparing Moving Magnet and Moving Coil phonograph cartridges, but nobody seems to talk about the differences between Moving Magnet and Moving Iron cartridges. So between those two, which is better? And in what ways do they differ in terms of sound?

Let me see if I understood this correctly: in a Moving Magnet type of cartridge, the coils are fixed and the magnets move, but in a Moving Iron cartridge, both the coils and the magnets are fixed, with the cantilever making a piece of iron move which then causes the magnets to induce a signal in the coils. Is this correct? Or did I misunderstand something?




Edited by Analog Kid - 23 Mar 2008 at 2:08pm

I'm working round to a reply...

coming up....

OK, reply as promised...

I don't have the historical dates but possibly around the 1940's phono cartridges were moving coil - yes moving coil. The development of small powerful magnets had not happened at that time so the coil being lighter, moved in sympathy with the stylus. However, the coils of these early MCs were quite big to get the number of ampere turns required to output the 10 milli-volts (mV, that's 0.01Volts) or so suitable for a "low-noise" valve phono input stage.

At that time people were into directly connecting cartridges to amplifiers because matching-transformers were expensive and hi-fi meant high fidelity instead of "look at me I'm rich"...

When magnet technology gave us the small powerful magnets required, the moving magnet cartridge happened and rapidly took over due to its lighter stylus load meaning it had a better frequency range.

Then somebody decided to make the low output moving coil.

I have heard it rumoured it was Joe Grado.

Great idea in every single way apart from whoever it was didn't understand electronics - especially noise matching - all that well...

So it needed a matching transformer - and hi-fi became a passtime of the rich - or "the ever so slightly overstretched"...

I have never liked low output MC for that reason alone (the noise matching): I have heard so much boasting of -90dB input noise but would love it if they could show me them measuring it!

The only way to make a MC stage without a transformer is to go all out for low noise and stifle the phase-response (you can't have your cake and eat it!) which makes MC sound "plodding".

In fact some reviewers are so addicted that when they hear an MC stage that sounds exciting and refreshing they hate it...

But hated as I am I keep trying.