MM (Moving Magnet)
The term moving magnet refers to the method used to regenerate the music signal from the record grooves. A tiny, powerful magnet is attached to the diamond tipped cantilever, which actually traces out the music signals from the record grooves.
The movement of the cantilever is transmitted to the magnet, which moves in a coil formed from very fine wires.
This movement of the magnet in the fixed coils generates the tiny electrical signal, which is then input into a special phono circuit to amplify it to a usable level. Typical output of this type of cartridge is 5 mV.
This allows the turntable output to be fed directly to a basic phono input. This type of cartridge is usually quite robust and is thus suitable for use by a beginner.
One of the advantages to using a moving magnet cartridge is a high output delivery. This typically means it is compatible with most any phono input on a stereo component. Many moving magnet cartridges also feature a removable and replaceable stylus, which can be important/convenient in the event of breakage or normal wear.
It generally costs less to replace a stylus than the entire cartridge itself.
One of the disadvantages to using a moving magnet cartridge is that the magnets tend to have higher weight/mass when compared to that of a moving coil cartridge. This greater value generally means that the stylus can't move as quickly over the record, which inhibits its ability to track the subtle changes within the groove's surface. This is where a moving coil cartridge has a performance advantage.
MC (Moving Coil)
An MC cartridge uses a similar motor system as the MM cartridge except that the magnet is fixed and the coils, which are fixed to the cantilever vibrate in response to the movement of the stylus tracking the record grooves.
The coils have fewer numbers of turns than that of the moving magnet, and are thus lighter and have much lower impedance and inductance. These factors allow for a wider bandwidth and better retrieval of low level information.
The MC phono cartridge is thus technically superior to the moving magnet however it does have a number of down sides, which prevents it from being widely use.
The main problem with it is the much higher cost. This is not just the higher cost of the MC phono cartridges themselves but also the cost of extra ancillary equipment. This is due to the low output of the MC phono cartridge, which is typically about 0.2 mV.
This requires the use of an extra amplification stage. Good quality step-ups as these are called do not come cheap. And if you use an outboard MC step-up device, there’s the additional cost of another pair of interconnects.
Thus for a person who is just starting out spinning vinyl, it is best to go with a modest moving magnet set-up. If properly done, it does not give anything away in terms of musical performance and enjoyment.
Compared with a well set-up MC based system, it would lose out in terms of low level resolution. Consider also that a poorly set-up MC based system can sound horrendous, and often worse than a mediocre MM based system. The greater definition of a MC cartridge can often work against it.
Which One to Choose?
Both moving magnet and moving coil cartridges provide great performance and are offered in a range of prices, shapes, sizes, and levels of quality. Both cartridge designs can sound excellent but the MC variant has the ability to go one step further and reach audiophile heights. Generally, the best value, lower cost, cartridges are of a MM design.
Those who are looking to achieve the best overall sound for turntables often choose the moving coil cartridge.
However, it really depends on the make and model of your turntable. Most turntables are compatible with only one or the other cartridge type. Some can use either kind. If you're unsure, a quick peek into the turntable's product manual will let you know which type is needed when it comes time for you to choose the next turntable cartridge (or stylus) replacement.