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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

Showing 4 responses by viridian

viridian's avatar
viridian
4,184 posts
 
Tom, how is that possible? He has 48db of gain in the phono preamp and 20db in the preamp for a total of 68db before the 18 to 30db of gain that the amp will have. At most he could be 7db short, but I would think that he could make it easy on this. Then again, I have never owned the Shelter.
Marty
viridian's avatar
viridian
4,184 posts
 
Wow! I knew you would set me straight on this one. That seems like a truckload of gain but these things are so cartidge specific, that's why I pointed out that you owned one and I don't. My only experience with super low output cartridges is with the Ortofon MC-2000 which had a little under .2mv output. With solid state amplification, at 200 ohms it would work just fine at around 70-72db of gain. My Denon 103D seems to work fine in the high 60s. Thanks again.
Marty
viridian's avatar
viridian
4,184 posts
 
OK, I tried the gain calculator at Kab Acoustics www.kabusa.com/pregain.htm and for a MC output of .2mv and a desired preamp output of .5 volt the calculator recommends 64db of gain. The problem with the whole game is that gain only tells you if you can drive your amp to clipping, not what the noise structure will be when you get there and not how badly you are compromising dynamics. A lot of this mess is very cartridge and stepup specific.
viridian's avatar
viridian
4,184 posts
 
Tom, my comments were made to point out how important noise structure is to the whole equation, not to call into question the veracity of your statement. You own the cartridge, as I said, I don't. I would always, always, defer to your expertise in this area. It is a fascinating area of discussion though. The calculator is just some mathematical game really and cannot substitiute for the real world experience that you, and other owners, have with a given setup. Now captured bearing versus unipivot, knife edge and oil bearing arms, that's where we can have a hearty and respectfull disagreement.
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