Posted on Fri, 16 Feb, 2024
Posted by Geoffrey Whittaker

How phono cartridges work

Moving magnet or moving coil phono cartridges, which is the best?

Today phono cartridges come in two main types, moving magnet and moving coil. This is normally shortened to MM or MC. Notably, there are also ceramic types that are used in inexpensive record players. A phono cartridge is an electro-mechanical device. In other words, the mechanical part refers to the unit that moves, normally the stylus and the arm that it is mounted to, known as the cantilever. The electro part refers to the electrical signal generating unit mounted inside the cartridge body.

The signal is generated in a similar way to a microphone or speaker drive unit. The main parts of a cartridge are the body, the cantilever , the suspension, and the magnet or coils. The cantilever holds the stylus at one end and the magnet or coils at the other end. The suspension allows the cantilever to pivot.

Moving magnet or moving coil?

The main difference between the two types of cartridge are the location of the magnet and coils. The moving magnet type has the magnet mounted on the end of the cantilever. This moves inside a fixed coil, on the other hand with moving coil designs this is reversed with the coils mounted on the cantilever. The main advantage of mounting the coils on the cantilever is lower mass and improved tracking. Particularly at higher frequencies.

Low or high output?

One striking difference between moving magnet and moving coil cartridges is the output signal level. Moving magnet cartridges have an output of around 5mV and an impedance of 47K. While moving coil cartridges may have an output of around 0.5mV. However moving coil units tend to have more variability with the output level and impedance. The lower output is often due to using smaller coils with thinner wire. This reduces the mass of the assembly allowing the stylus to track more accurately. Consequently, the music has more detail

Ortofon 2M blue

Ortofon cartridges are often fitted to mid-priced turntables and the Ortofon 2M blue is a good example of a high-performing budget cartridge. The frequency response is good at 20Hz to 20 KHZ and the output is a typical 5.5mV. It is also fitted with and elliptical stylus that is thought to improve high frequency tracking. They can be had for around £200

Quintet Blue

On the other hand the Ortofon Quintet Blue is a MC design with an output of  0.5mV. It is also reasonably priced at around £500. The sound is detailed with good dynamics and resolution. The perfomance is high end without the high cost.

Pre-amp requirements

Another issue with moving magnet or moving coil phono cartridges is the need for a high qaulity preamp. The lower output needs a preamp with more gain and this tends to increase noise and distortion. The turntable also needs to have better bearings and tracking ability to take advantage of a moving coil cartridge.  Moreover, the more intricate design also costs more to manufacture. Next, we look at a budget MM phono stage as well as a high end unit intended for MC cartridges.

Budget phono preamps

The ProJect Phono Box MM  is a good quailty basic phono stage. The unit uses an external power supply. Notably, this reduces the chance of any hum and noise being introduced. It is a good choice if you main amplifier does not have a phono input. It is also inexpensive at less that £100.

A high end phono preamp with MC cartridge matching

On the other hand the best performance with MC cartridges can be obtained from the Pro-Ject Tube Box DS2 Valve Phono Stage. This unit has a number of settings that can be used to “fine tune” the input characteristics. As a result it can be matched to any type of MC cartridge.

The input loading or impedance can be varied as can the gain. There is also a low rumble filter and outputs for two turntables. The design is dual mono and uses two ECC 83 dual triode valves. Valves are loved by audiophiles for their warm sound.

What is impedance?

You will often see impedance mentioned in the specifications for phono cartridges and this is one of the main differences between moving magnet or moving coil phono cartridges. So what is impedance? This is a complicated subject but basically impedance is a combination of resistance, capacitance and reactance. All these things have an effect an an AC signal such as an audio signal. The effect is also frequency dependant, to a degree. In effect it can be though of as the resistance of the audio source and needs to be matched to the input impedance of the preamp that follows it. For example the impedance of a MM cartridge is around 47K while MC cartridges vary more widely and are usually around 10 Ohms. The preamp input should be around ten times the source impedance, in this case 100 ohms.

Performance – moving magnet or moving coil phono cartridges, which is best?

The choice of MM or MC cartridges is mainly down to the price of the turntable and personal preference. MM carriages can have a more robust sound due to the higher output. Whereas MC cartridges are more refined and clear. Notably, for sub £1000 turntables moving magnet is probably the best choice. however, For high end turntables MC units will extract the most information from the groove.

Price

The price range for MM cartridges varies from less than £50 to close to a £1000. On the other hand MC carriages start at around £150 and can extend up to close to £8000 .The My Sonic Lab Signature Gold MC Phono Cartridge is a top of the line MC cartridge with a fast transient response and low distortion. The use of exotic materials and hand manufacture are the main drivers of price.

Conclusion – Moving magnet or moving coil phono cartridges, which is best?

The choice of which cartridge type to use is a combination of budget, the cost of the turntable itself ,and personal preference. Sub £1000 turntables are probably best with an MM cartridge. While high end units can best take advantage of the finesse and better high frequency perfomance of an MC design.

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