Magnetic cartridge facts for kids
A magnetic cartridge is a small, important part of a record player (also called a turntable). It's like a tiny electric generator that turns the bumps and wiggles in a record's groove into an electrical signal. This signal then gets sent to an amplifier and finally to speakers so you can hear the music.
The cartridge has a tiny "needle" called a stylus. This stylus is usually made of a hard gemstone like diamond. It sits on a small arm called a cantilever. As the stylus moves along the record's groove, it vibrates. These vibrations make a tiny magnet move near some coils of wire (or coils move near a magnet). This movement creates a small electrical current, which is the sound signal.
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How Record Players Changed Over Time
The first successful electric record player parts came out in 1925. They used big magnets and steel needles that wore out quickly. These early parts were very heavy. They pressed down on records with a lot of force, measured in ounces, not grams!
By the late 1930s, lighter parts called "piezoelectric crystal pickups" became popular. They still used disposable metal needles. After World War II, people started using longer-lasting needles made of sapphire or osmium. But most records were still made of a rough material that wore down needles fast.
In the late 1940s, new types of records came out: the 33⅓ rpm vinyl LP and the 45 rpm vinyl "single". These records needed smaller, more precise needles. Sapphire and diamond became the standard materials for these new needles.
At first, these new needles were found in crystal or ceramic cartridges. These were common in simple, portable record players because they were tough and cheap. Even today, many "retro" record players use ceramic cartridges.
However, in the 1950s, new, lighter magnetic cartridges appeared. Music fans loved them because they made music sound much better. They also put less pressure on records, which helped records last longer. Today, magnetic cartridges are the most common type used in good quality sound systems.
Parts of a Magnetic Cartridge
A magnetic cartridge has several key parts:
- Stylus: This is the "needle" that touches the record. It's usually a tiny, polished diamond.
- Cantilever: This is a small arm that holds the stylus. It vibrates when the stylus moves in the groove. It's often made of strong, light materials like boron or aluminum.
- Magnets and Coils: These are the parts that create the electrical signal. Either a magnet moves near coils, or coils move near a magnet.
- Body: This is the main part of the cartridge that holds everything together. It connects to the record player's arm, making sure the stylus tracks the groove accurately.
Some magnetic cartridges have styluses that you can replace easily. This means you don't have to buy a whole new cartridge when the needle wears out.
Different Kinds of Magnetic Cartridges
In high-quality sound systems, magnetic cartridges have replaced older crystal and ceramic types. Magnetic cartridges usually give better sound and cause less wear on your records because they use lighter pressure. They also produce a smaller electrical signal, so they need more amplification.
Moving Magnet (MM) Cartridges
In a moving magnet cartridge, the stylus cantilever has a tiny magnet on it. This magnet moves between two sets of fixed coils of wire. As the magnet vibrates, it creates a small electric current in the coils.
Because the magnet is small and light, the stylus can follow the record groove very accurately. This means it needs less downward pressure to play the record.
Some cartridges, called "moving iron" or "induced magnet" types, are similar. Instead of a magnet on the cantilever, they have a small piece of iron that moves. A larger, fixed magnet provides the magnetic field.
Moving Coil (MC) Cartridges
Moving coil cartridges work in the opposite way. Here, the coils of wire are attached to the cantilever, and they move within the magnetic field of a fixed magnet. The coils are very tiny and made of fine wire.
Because these coils are so small, they produce a very tiny electrical signal. This signal is easily affected by noise. So, moving coil cartridges often need special preamplifiers or "step-up transformers" to boost their signal.
Some "high output" moving coil cartridges exist that produce a stronger signal, similar to moving magnet cartridges. Moving coil cartridges are often more expensive because they are very precise. Many serious music listeners prefer them for their sound quality.
Moving Micro Cross (MMC) Cartridges
The MMC design was invented by a company called Bang & Olufsen. It's a special kind of "moving iron" design. In an MMC cartridge, the magnets and coils stay still. A tiny "micro cross" moves with the stylus. This cross changes the distance between its arms and the magnets. This design is said to offer better sound separation between the left and right audio channels.
Moving Magnet vs. Moving Coil: Which is Better?
Moving magnet (MM) cartridges are usually more common and often found in less expensive sound systems. Moving coil (MC) cartridges tend to be in higher-end systems. People often debate which type sounds better, and it can be a matter of personal preference.
Here are some points to consider:
- Cable Effects: MC cartridges are less affected by the type of cable connecting them to the amplifier. MM cartridges can be more sensitive to cable quality.
- Moving Mass: It's often thought that MC cartridges have lighter moving parts, which helps them track records better. However, some high-quality MM cartridges can have very low moving mass too.
- Other Factors: The shape of the stylus tip, the material of the cantilever, and how the stylus is mounted can also greatly affect the sound quality. These factors can sometimes be more important than whether the cartridge is MM or MC.
MM cartridges usually produce a signal of 3-6 millivolts (mV). This works well with standard "MM inputs" on preamplifiers. MC cartridges come in two main types:
- Low Output: These produce less than 1.0 mV, sometimes even as low as 0.3 mV. They need special, very sensitive "MC inputs" on preamplifiers, or an extra amplification stage.
- High Output: These produce more than 1.5 mV, making them more compatible with standard MM inputs.
