What is the difference between a moving magnet and moving coil cartridge? Does it matter?

Moving Magnet

In a moving magnet cartridge, the stylus (typically a diamond) is attached to a rigid cantilever, which has a small magnet on the other end. Within the cartridge body, near the magnet attached to the cantilever, are a pair of coils. The movement of the magnet, caused by the stylus running through the groove of the record, generates a current in these coils which can then be picked up by the phono stage.

Moving Coil

As the name suggests, in a moving coil cartridge, the magnet and the coils have switched places. So, the cantilever has the stylus at one end and a pair of coils at the other. The cartridge body then contains the magnets. As with a moving magnet cartridge, the stylus running through the record groove cause movement in the cantilever. This time however it is the coil that moves within the magnetic field rather than the magnetic field moving around the coils to generate the signal which passes to the phono stage.

Moving Iron?

I have to admit, that until writing this blog I had always incorrectly assumed that Moving Iron was just another way of saying moving magnet. Magnets are made from iron, right?

It's not far off but there is a subtle difference. In a moving iron cartridge, both the magnet and the coils are in fixed positions within the cartridge body and there is a small hollow temporary magnet or armature attached to the cantilever. This small hollow piece of iron has a magnetic field induced in it by the stationary magnet within the cartridge, the movement of the armature then induces a magnetic flow within the poleshoes which are within the fixed coil. This generates the necessary current to be picked up by the phono stage.

Effectively, this means that with moving iron cartridges, you can get greater detail than a standard moving magnet while retaining the high output.

Moving magnet cartridges tend to have an output of between 2mV and at the extreme 10mV, most typically being between 3mV and 5mV.

Moving Iron carts have a similar output to moving magnet and can therefore be used with a moving magnet phono stage.

Both of these types of cartridge need a phono stage with a 47KOhm input loading and usually around 40-47dB of gain. Any moving magnet phono stage will be capable of running these cartridges and no adjustment need to be made.

Moving coil cartridges have a much lower output voltage, due to the size of the coil that can be attached to the cantilever. They can be as low as 0.15mV and rarely get above 1.6mV. This means that they need a phono stage tailored to deal with these low outputs. Usually these will have adjustments so you can match the input loading, both impedance and capacitance to the cartridge manufacturers specifications. There is normally a gain adjustment too.

Moving coil cartridges can be used with a moving magnet phono stage but to do so requires a pair of transformers, one for each channel to sit between the cartridge and the phono stage.

So then, does it matter?

Yes, it does. It matters both for reasons of compatibility and fidelity.
In terms of compatibility it is simple, buy the wrong cartridge for your phono stage and it simply won't work. Running a moving coil cart into a moving magnet stage won't provide enough gain and your turntable will barely audible. A moving magnet cartridge being put through a moving coil stage will overload the input and produce a distorted sound.

When it comes to fidelity, a moving coil cartridge has the benefit of a small coil on the end of the cantilever allows for greater detail to be retrieved from the record. This because there is a much smaller mass moving, so the response to the contour of the record groove is faster and can be more subtle. As discussed earlier this means that the signal produced is more delicate and needs more gain to be added than a moving magnet does. This means that the phono stage is more important to the end result as well.
That's not to say that you can't get very good results with either moving magnet or moving iron, just that the more you move into the world of high end turntables the less you will see moving magnet/iron, to obtain that detail that we are all chasing, moving coil is usually the best answer.

Thanks for reading, and feel free to contact us if you need more information on this subject.

Mike - Audio T Manchester

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