In a stereo moving-magnet cartridge (MMC), a miniscule permanent magnet rests on the end of the stylus cantilever suspended between two coils—one for the left and one for the right audio channels. As the name suggests, the magnet moves (vibrates) between the two coils and, in so doing, induces a small current in them. Since the magnet is extremely small it weighs very little, requiring a lower downward (tracking) force to accurately travel the record grooves.
The only marked difference between an MMC and a moving-iron cartridge (MIC) is a tiny piece of iron or other light, ferrous alloy that replaces the magnet on the end of the cantilever. In this case, the iron is lighter than the magnet, further reducing tracking force while boosting tracking accuracy
Moving Coil
A moving-coil cartridge (MCC) uses an inverted moving magnet design. The coils attach to the stylus cantilever, and the permanent magnet resides near the coils. Since space is beyond extremely limited, the coils are tiny, using extremely fine wire. This limitation on coil size results in an extremely low output, i.e., in the microvolt range.
With an output of around 100 µV to 300 µV, MCCs are very susceptible to noise and hum. In addition to an RIAA preamp, these cartridges require an additional amplifier stage or step-up transformer prior to the RIAA frequency-compensating preamp. There are, however, high-output MCCs on the market capable of delivering output levels comparable to MMCs.
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作者: Leo Yeh
