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phono pre loading and gain question

I have a Motif mp-11 phono pre. Inside, through switches, the gain can be set between 40, 45, and 48 db. On the front is a knob selector for loading with positions: 70 ohm, 100, 150, 250, 470, 1k, 2k, 5k, 10k, 20k, and 47k. I have read most of the threads and am still confused about how low of an output mc I can use. This feeds into a Sonic Frontiers preamp with 20db gain. I don't want to get a step-up transformer if I don't need one...but I would like to try a Shelter cartridge out. Also, why would my phono pre have so many loading choices but so little maximum gain. One more thing...are step ups very prone to noise or hum. thanks
skeyebox
twl
3,251 posts
 
You'll be about 15-20db short on gain for a Shelter, with that setup. The loading choices are an entirely different matter than the gain amounts. The loadings are to properly provide the cartridge with the correct characteristics that it is meant to drive. The gain settings are to increase the output of the cartridge to a useable level for the preamp to accept. Both are important to get the best from the cartridge.

Step up devices are not inherently noisy, but some cheaper head amps might be. Transformers may have some rolloffs or bass problems if you don't get a good one. The key is to buy a quality one of whatever type you choose.
skeyebox OP
27 posts
 
Thanks for the response...but if I use a step-up then I just leave the loading on my phono pre on 47k?
twl
3,251 posts
 
With a step up transformer, the phono section would be loaded at the 47k ohm setting, and the load for the cartridge would be set at the input of the transformer, at an amount about 1/2 what is suggested as the normal load for going direct in to the phono stage, unless there is some specific directions by the manufacturer of the cartridge that it should be loaded at "X" for direct input, and "Y" for transformer. Some cartridge spec sheets will specify the loadings for both direct input and transformer.

I use a Shelter 501 with a step up transformer, and find that it works very well at a transformer loading of 40 ohms.
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