Moving Magnet vs Moving Coil – The 3 Things You Need To Know
In this article, we will discuss Moving Magnet vs Moving Coil and cover the major 3 things you need to know about them. The phono cartridge has a decisive influence on the sound of your system when you play records; therefore the time you spend learning about this key component is well invested!
Once you are clear about the pros and cons of each cartridge design, you can better decide which one is best for your setup.
Let’s dive in!
Moving Magnet vs Moving Coil: Introduction
Moving Magnet (MM) and Moving Coil (MC) cartridges function on the same principle: mechanical vibrations are converted into an electrical signal. In both MM and MC designs, the cartridge cantilever holds a diamond stylus to track the record groove on one end, and transfers the vibrations to the other end, where the generator is placed.
The generator, may it be MM or MC design, works according to Faraday’s first law of electromagnetic induction. This law states that whenever a conductor is placed in a varying magnetic field, an electrical voltage is induced in that conductor. In the case of both MM and MC cartridges, the above-mentioned conductor is a coil of wire, and a strong magnet creates the magnetic field.
End of the similarities between MM and MC designs.
Now let’s see their difference:
In a Moving Magnet cartridge, the coil is stationary and the magnet is attached to the vibrating cantilever.
Inversely, in a Moving Coil cartridge, the magnet is stationary and the coil is attached to the vibrating cantilever.
Now that we know that MM and MC designs are 2 distincts approaches to get the same result, does it make a big difference whether you move the magnet and hold the coil or vice versa?
Well yes, and here are the 3 things you need to know to better understand why:
1. High vs Low Moving Mass
The first thing to understand is the notion of moving mass.
In a MM cartridge, the moving mass is the stylus / cantilever / magnet assembly, and in a MC cartridge, the moving mass is the stylus / cantilever / coil assembly.
The coil of a MC cartridge is often significantly lighter than the magnet of its MM counterpart. We therefore say that MM cartridges have a higher moving mass than MC cartridges.
The larger moving mass of MM cartridges implies that their stylus has more inertia than the stylus of MC cartridges while tracking the record groove. In other words, the stylus of a MM cartridge cannot react as quickly over the record, limiting its capacity to track subtle changes in the groove’s surface.
This is therefore where MC cartridges tend to have a first performance advantage. Sonically, this advantage translates into higher micro-detail resolution, and better dynamics.
Other parameters like the cantilever material and its length also affect the moving mass of a phono cartridge. For MC cartridges in particular, the size of the coil is important and we will see that later on.
2. High vs Low Inductance
The second key difference between MM and MC cartridges is that of inductance.
As MC cartridges have a much smaller coil than MM cartridges, we can say that MC cartridges have a far lower inductance than their MM counterparts.
Why is this important?
Because the inductance of the cartridge, the capacitance of the phono cable, and the resistance & capacitance of the phono stage input altogether form a harmonic oscillator circuit, also called RLC circuit.
This kind of circuit has a ringing resonance at a certain frequency, and a steep roll-off of frequencies above the resonant point, also called low-pass filter. The lower the inductance of the coil is, the higher the frequency of the resonance is, and vice versa.
So for MC cartridges, the resonant frequency will be way up in the ultrasonic range, and changes of cable or phono stage capacitance won’t have much of an audible impact. The ultrasonic ringing can also be damped by loading the cartridge with the appropriate resistance at phono stage input level.
With MM cartridges, the higher inductance and capacitance will have an impact on the frequency response of the system in the audible range. For good MM cartridges, the resonant frequency often falls somewhere in the top two octaves of the audible range, with all frequencies above that being rolled-off.
To summarize: MC cartridges have a lower inductance than MM cartridges, so their frequency response is flatter and more extended. In comparison, MM cartridges tend to have an odd frequency response, and a lack of high frequencies.
For stereo cartridges, smaller coils also means less crosstalk between them. As a result, MC cartridges tend to have better channel separation (+10dB or more) than MM cartridges, which translates acoustically into better stereo imaging.
3. High vs Low Output
The third crucial difference between MM and MC cartridges is their output level.
The output level of a phono cartridge is measured in millivolts (mV), and largely depends on the size of the cartridge coils.
We now know that MM cartridges have larger coils than their MC counterparts. As a result, MM cartridges have a higher output level (typically 3 to 7 mV), and can be connected to the standard phono inputs of a stereo amplifier or receiver. Easy and cost effective!
For MC cartridges and their very small coils, it is a different story. Their output level is much lower, typically between 0.2 and 0.6 mV, so they need an extra 20 to 26dB amplification/gain compared to MM cartridges.
This extra gain can be achieved with a MC Step-Up Transformer or a dedicated MC Phono Preamplifier. We recommend MC Phono Preamplifiers rather than MC Step-Up Transformers because the latter are prone to magnetic noise. The low current generated by the MC cartridge often creates an audible magnetic noise (Barkhausen noise) in the MC Step-Up Transformer core. Some very good MC Step-Up Transformers do exist, but they are extremely expensive.
So to summarize: MM cartridges and their high output are much easier to work with in terms of equipment. MC cartridges require a dedicated MC Phono Stage/Preamplifier, or a MC Step-Up Transformer between the turntable and the MM Phono input. The extra equipment can be very costly and need to be taken into account when choosing between a MM or MC cartridge!
Moving Magnet vs Moving Coil: Conclusion
You now understand the 3 main things about MM vs MC cartridge, as well as their implications.
All these information can be summarized as follows:
Moving Magnet vs Moving Coil: Frequently Asked Questions
What about High Output MC cartridges?
High Output MC cartridges are MC cartridges with bigger coils, and their output is generally above 2mV. They generally have an impedance loading of 47kOhm like MM cartridges, and they can be connected to the MM input of a phono stage.
Such cartridges may offer a better moving mass than their MM counterparts, but their inductance will be higher than low output MC cartridges and therefore bring the same issues: high frequency roll-off, and cross talk.
They may be an interesting middle ground between MM and MC cartridges, as they don’t require more gear than a MM cartridge.
What about the removable stylus?
In most MM cartridges, the moving parts (stylus / cantilever / magnets assembly) can be removed and replaced. The stylus / cantilever / coils assembly of an MC cartridge is linked to the cartridge’s connector pins. Hence when the stylus of an MC cartridge becomes worn, the cartridge must be returned to the manufacturer for retipping.
The owner of a MM cartridge can therefore easily replace the stylus / cantilever / magnets assembly by himself, which is quite convenient. However this convenience has a drawback: the mechanical stability of the moving parts of a MM cartridge is in general inferior. This can translate in all kinds of minor sonic artefacts.
Which cartridge has a longer lifespan, MM or MC?
The lifespan of a cartridge depends on a myriad of factors:
- The quality of construction of the cartridge
- The shape of the stylus (e.g. conical styli wear much faster than line contact ones for example)
- The quality of the stylus (e.g. industrial vs natural diamond)
- The vertical tracking force of the cartridge
- The quality of the cartridge alignment on the headshell
- The record cleanliness
- And so on…
It is therefore impossible to predict if a cartridge will have a longer lifespan just because it is MM or MC.
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Gregory de Richemont
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