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In Reply to: Gain for low output cartridges posted by Hujo on September 13, 2006 at 17:31:09:
If you have already a preamp with a phono stage, or a stand alone phono stage, for MM cartridges then you need only a step up transformer.
For the missing 20dB it should have a step-up-ratio of 1:10. If you'd like to damp your cartridge with a load resistor, like Garth or others her in the forum are doing, you need to increase the step-up-ratio for example 1:33.
Follow Ups:
Can someone explain the relationship between the output and the damping/loading/ohms issue?
I've researched the archives and just don't understand it.
Thanks
The cartridge output is distributed proportionally across its internal impedance and its load impedance. For example, if a cartridge produces a voltage of 1-mV and has an internal impedance of 12-ohms with a preamp load impedance of 12-ohms, then it delivers only 0.5-mV to the preamp load. This is somewhat simplistic, but fairly accurate for impedances that are primarily resistive, which is the case for low-output moving coils and phono preamps.If you want to deliver more of your cartridge’s voltage to the preamp load, you want the preamp load to be larger than the cartridge’s internal impedance. In the above example, if you terminate the cartridge with 100-ohms, it will deliver (100/112) x 1-mV = 0.89-mV to the phono preamp.
responding to this and my other post on preamps. I don't have the ability with my current equipment to change the loading, so I guess I need to be careful about what the recommended cart loading is for the ones I'm thinking of purchasing.
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