Burn in Step up transformer with ipod.

I would err on the side of caution and not extrapolate from Kevin Carter's practices with the Lundahl transformer to other transformers, which may have higher step-up ratios and be different designs. Putting a 1 volt signal into a 20 db step-up will result in 10 volts on an output that is intended to handle a few millivolts.

Good comments by JJ. Personally, though, I would not put a stepped up line-level signal into a phono stage whether it is turned on or not, especially if it is solid state. It's easy enough to get a resistor at Radio Shack or elsewhere and not take any chances.

Regards,
-- Al

If I plug the output of the mc transformer to a line input in the preamp( not phono) what load would that supply the mc transformer? Or does only a phono input provide the right load to the step up?

Also by plugging to the line input, that would prevent any damage to the phono stage.

If I plug the output of the mc transformer to a line input in the preamp( not phono) what load would that supply the mc transformer?

That's a good thought, at least potentially. The load impedance will be approximately equal to the specified input impedance of that input. Often 47K, and usually somewhere between around 20K and 100K.

Or does only a phono input provide the right load to the step up?

No. If the line level inputs and the phono input have a similar input impedance, the transformer (and the source) won't know the difference. But there would be much less chance of damaging a line level input than a phono input.

Still, though, I'd be hesitant to send 10 volts or so into a line level input of a solid state preamp for prolonged periods of time, even if it is turned off, without being familiar with the design of the input circuit or obtaining an ok from the manufacturer. I doubt that it would be a problem, though, with tube equipment.

Regards,
-- Al

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.

07-26-13: John_tracy
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.

John, take a look at the schematic shown on the last page of the manual for the Hagerman Bugle2 phono stage. Note that the input signal goes through a low value resistor into an OPA2134 op amp, which uses a FET input stage. Here is the datasheet for the OPA2134. Note in the Absolute Maximum Ratings listed on page 3 ("stresses above these ratings may cause permanent damage" as stated in note 1 below the listings) that the absolute maximum input voltage is specified as being 0.7 volts beyond the power supply "rails" (voltages) that are supplied to the device.

That kind of absolute maximum specification of input voltage, specified relative to the supply rails, is very common in the case of op amps and other analog integrated circuits.

When the phono stage is turned off the supply rails are of course zero. Therefore at the positive and negative peaks of a 10 volt rms sinusoidal input that absolute maximum rating will be EXCEEDED by (10 x 1.414) - 0.7 = 13.4 volts. (The 1.414 factor converts rms to peak, of course).

And even when the device is powered up, its supply rails are approximately +/- 10 volts in this phono stage (as indicated on page 7 of the manual), and so the absolute maximum rating of its input will be violated by 3.4 volts at the positive and negative peaks of the waveform.

Will that damage the device, or degrade its long term reliability, if it were done for a prolonged amount of time during a burn-in process? I don't know. But it certainly strikes me as a significant risk, and as very bad practice.

That was the kind of situation I was envisioning when I offered my previous comment, not an oscillation scenario. And also in the back of my mind was the fact that bipolar transistors, which might be used in other designs, commonly have very low absolute maximum voltages specified for their base-to-emitter junctions in the reverse direction, in the neighborhood of 5 volts or so.

Regards,
-- Al