Warning, Never Use A Meter!

[walpurgis]

Never use a meter to test continuity of cartridge coil windings.

This applies to MM and MC types and low output MCs and Deccas in particular. The little current that is delivered by a meter can still be enough to fuse the very fine coil windings, although it's usually the lead outs that melt, as they are least able to dissipate heat. I have come across cartridges that have been destroyed in this fashion. An Entre and two Deccas to be precise, not done by me I might add.

[steveledzep]

Good tip....thank you !

[NRG]

Er why would you?

[Barry]

I suspect those cartridges you found with o/c connections had been continuity tested using an old analogue ohm-meter, such as an AVO. AVOs used a meter with an fsd of 50uA.

Modern digital ohm-meters pass very little current. I have checked the continuity of a couple of low-output MCs without causing any damage.

Take the example of the Ortofon SPU. This will produce 200uV into say 100 Ohm. The current is therefore 2uA. If the ohm-meter is current limited to 2uA, then the voltage across the 6 Ohm coil will be 12uV. The motor action of the cartridge acting 'in reverse' will deflect the stylus only a little, and the heat dissipation will be within the manufacturer's design figure.

I imagine MC manufacturers do something similar to check the connections of their cartridges.

[walpurgis]

Er why would you?

Many people do. Look on eBay, sellers stating that they have tested the coils.

[walpurgis]

I suspect those cartridges you found with o/c connections had been continuity tested using an old analogue ohm-meter, such as an AVO. AVOs used a meter with an fsd of 50uA.

Modern digital ohm-meters pass very little current. I have checked the continuity of a couple of low-output MCs without causing any damage.

Take the example of the Ortofon SPU. This will produce 200uV into say 100 Ohm. The current is therefore 2uA. If the ohm-meter is current limited to 2uA, then the voltage across the 6 Ohm coil will be 12uV. The motor action of the cartridge acting 'in reverse' will deflect the stylus only a little, and the heat dissipation will be within the manufacturer's design figure.

I imagine MC manufacturers do something similar to check the connections of their cartridges.


No doubt manufacturers do have a continuity and measurement test and employ suitable equipment.

But the true output of the average multimeter is likely to be an unknown quantity and will probably vary from unit to unit to a degree, so what's safe?

As I say, I've come across dead cartridges where the fine wire has definitely been fused, i.e. melted ends visible under magnification.

Best to exercise caution I'd say.

[Barry]

No doubt manufacturers do have a continuity and measurement test and employ suitable equipment.

But the true output of the average multimeter is likely to be an unknown quantity and will probably vary from unit to unit to a degree, so what's safe?

As I say, I've come across dead cartridges where the fine wire has definitely been fused, i.e. melted ends visible under magnification.

Best to exercise caution I'd say.

Sound advice Geoff.

The current passed will depend not only on the make of ohm-meter but on the resistance range. This information will be stated in the manufacturer's data, or it can be measured.

If the sensing current is too high, it can be limited by fitting a current limiting resistor.

Like a lot of things, if you know what you are doing it's OK; if you don't - leave well alone.

[OneyedK]

Never use a meter to test continuity of cartridge coil windings.

This applies to MM and MC types and low output MCs and Deccas in particular. The little current that is delivered by a meter can still be enough to fuse the very fine coil windings, although it's usually the lead outs that melt, as they are least able to dissipate heat. I have come across cartridges that have been destroyed in this fashion. An Entre and two Deccas to be precise, not done by me I might add.
Are you sure it was a meter that killed those carts and not a Tube préamp?