I can't believe the amount misinformation and bad advice that is being spread on the web by these forums. Against my better judgement let's address some of the issues raised on this tread:
1 - an AC signal of .2-.3Vrms will not saturate the core of a MC transformer. It will in fact be more effective at demagnetizing the core than the typical .3-.4mV signal from a MC cartridge. BWT, it is a myth that prolonged core saturation will damage a MC transformer. Now if your source of a burn in signal has a DC offset at its output it will magnetize the core. In that case inserting a capacitor in series with the output will block any DC.
2 - you won't "burn out" the windings of a MC transformer by feeding it a line level signal. To see why consider this thought experiment. Take a large power transformer. Measure the DC resistance of its primary winding. Typically this is in the range of 0.3 ohms or so. Take a 0.3 ohm resistor and plug it into a wall socket. It will probably explode with a big puff of smoke. Now plug in the primary winding of the power transformer with an unloaded secondary. Same DC resistance but no fireworks. Why? Because the transformer's winding is an INDUCTOR! Inductors appose the flow of current. That's what they do. Now MC transformers do have fewer turns on their primary than line level input transformers (to better match the low impedance of a MC cart.) , they still have enough inductance that any line level signal will not "burn out" the windings. As a note, most manufactures of MC transformer use heavier guage wire on the primary of a MC transformer than they use on a line level input transformer to limit I*2R losses.
3 - as to using an inverse RIAA network this will certainly do no harm, I just don't see the point. These things are very useful for measuring a phono preamps frequency response. But if you have ever used one to do that with a MC transformer input you may be left wondering why your unit has no bass response. The reason for this is the MC transformer needs the low source impedance of a MC cart. The inverse RIAA network presents the transformer with a very high source impedance. The result of this interaction is a rolled off bass response. It actually might take longer to burn in your transformer with this lack of excitation from low frequency signals.
4 - as to the possibility of damaging a solid state phono pre by inputing a 10Vrms signal into a unit that is turned off, get real. If someone can come up with a real example of this, show me the circuit and I will eat my words. A well designed unit should not be damaged even turned on. If that signal some how shocked the input stage into some type of destructive oscillation then the unit was probably crap to begin with.
