Cartridge Loading for a phono pre amp

@holmz 

Back EMF?? No. Any cartridge is a generator of power. When the load on any generator is reduced in resistance, more current can flow. This energy has to come from somewhere (otherwise a new branch of physics would be created...) and it comes in this case from the motion of the stylus in the groove- the cantilever becomes harder to move.

You can easily demonstrate this principle for yourself. A loudspeaker operates on the same principle of a moving coil in a magnetic field. If you have a woofer with nothing connected to it you'll find it easy to move the cone with your hand. If you then place a short across the terminals of the speaker you'll find that the cone is a lot harder to move.

What the load resistor does is three things: it detunes the resonant peak I mentioned earlier, thus eliminating the RFI and it causes the cantilever to be stiffer, possibly reducing the ability to trace high frequencies and certainly affecting the mechanical resonance of the cartridge and arm combination.

So you solve a problem for a phono section with a design bug, in exchange for introducing possible tracking issues. Not a good set of options IMO.

Thanks @atmasphere .

I was under the impression that the current from the motor was the same with and without the load, so 47k would be a higher voltage across the resistance, and lower resistance would be less voltage.

Looks like I got it backwards.

The options I have are as follows: 47K, 1K, 560R, 470R, 100R, and 47R.

There are three more options worth experiments:

257R (560R+470R)

322R (1K+470R)

362R (1K+560R)

Also ... with an output of 1.1 you might start at 52 db of gain.

Always start with 47K to see if the preamp works with RFI at its input. If yes (the preamp is unperturbed by RFI), this will get you the best sonic performance. If it sounds better with lower resistance loads, then the preamp does not handle RFI well.