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A customer called us today who had some concern that the coil resistance of his moving magnet (MM) phono cartridge did not measure correctly, or so he thought. He pointed out that the recommended terminating resistance for his phono cartridge is 47,000 Ohms (47 kOhm) and expected the phono cartridge coil resistance to measure that same value when disconnected from his preamplifier. He had measured both channels using a digital multimeter to be around 600 Ohms and was wondering if there was a failure in the cartridge.
The answer is that the recommended terminating resistance for a magnetic phono cartridge is not supposed to be equal to its internal coil resistance. In fact, moving magnet phono cartridges should read somewhere between 500 to 1,000 Ohms typically when measured with a multimeter (0.5 to 1.0 kOhms)*. So, the good news for the customer was that his cartridge coil resistance reading was right in the correct window.
I just thought that this would be a good posting as a general reference in case anyone else ever needs to verify the coil resistance of their MM phono cartridge.
ps - MC coil cartriges will exhibit a much lower coil resistance values compared most of the MM types. They are typically in the 30 to 50 Ohm range.
*Note 1: These are approximate values and may vary +/- 5 % between the left and right channels on a given cartridge,
Note 2: Some very low output Voltage MM cartridges may exhibit coil resistance values down in the 40 Ohm range, but these are quite uncommon.
The answer is that the recommended terminating resistance for a magnetic phono cartridge is not supposed to be equal to its internal coil resistance. In fact, moving magnet phono cartridges should read somewhere between 500 to 1,000 Ohms typically when measured with a multimeter (0.5 to 1.0 kOhms)*. So, the good news for the customer was that his cartridge coil resistance reading was right in the correct window.
I just thought that this would be a good posting as a general reference in case anyone else ever needs to verify the coil resistance of their MM phono cartridge.
ps - MC coil cartriges will exhibit a much lower coil resistance values compared most of the MM types. They are typically in the 30 to 50 Ohm range.
*Note 1: These are approximate values and may vary +/- 5 % between the left and right channels on a given cartridge,
Note 2: Some very low output Voltage MM cartridges may exhibit coil resistance values down in the 40 Ohm range, but these are quite uncommon.