Phono stage overload margin ??

Under what circumstances a phono stage would become "overloaded".
What exactly is "overload margin".

In the December issue of Stereophile, Mike Fremer describes the Esoteric E-03 phono preamp as: "The MM gain is specced at 44db and the MC gain at 66db with ultralow noise specs of -137db/v (MM) and -140db/v (MC) with very comfortable overload margins of 180mv (MM) and 9mv (MC) presumably both at 1kHZ. The E-03 should proce compatible with all cartridges other than MC's with output below 0.25mv which is close to the output of the Ortofon A90".

For sake of discussion (although i am talking in general terms here), my system consist of ARC Ref Phono2 with gain of 45-51-68-74db. Cartridge is an A90 along with ARC Ref3 LE with 11.6db gain.
Based on the specs shown here at the Esoteric site, Mikey should have referred to those numbers as the "overload point," or the "rated maximum input level," rather than the "overload margin" (which would refer to the difference between rated maximum input and rated cartridge output). Although in this case the quantitative difference between these terms is pretty much insignificant.

The numbers simply mean that the phono stage will not overload until an input exceeding 180mv is applied at the MM input, or an input exceeding 9mv is applied at the LOMC input, at 1kHz. Those are indeed very comfortable numbers, as is the 250mv maximum input spec of your Ref Phono2 (although it is not quite clear if that refers to just the low gain setting, or to both gain settings).

Some phono stage overload specs are defined relative to output levels, rather than input levels, so care has to be used when comparing these numbers with those of other components.

As you probably realize, under standard test conditions MM cartridges typically have output amplitudes in the rough vicinity of 5mv, and LOMC's are a fraction of a mv. I don't know how much those output numbers might be exceeded by under worst case conditions, but I doubt that even the initial high frequency crack of the cannon shots on the infamous Telarc 1812 Overture, as boosted by RIAA pre-emphasis, would come remotely close to those overload numbers.

-- Al
The simple explanation is a cartridge might output 10 times its rated output on loud passages. So the A90 @ 0.25mv would output 2.5mv which is less than the 9mv of the Esoteric.

I disagree with Fremer about it not being able to handle carts with less than 0.25mv. In a well put together system and especially with those noise specs it should be able to use almost any cart.
Smoffatt, I have a 2002 model ARC Phono Ref (69db MC gain) and the Manual suggests not using MCs of more than 0.30mV, and from using various carts over the years I now know that it tends to sound better with carts of around 0.25mV that with those at 0.30mV and more. I am not that technical but I believe that some designs will have a sweet spot input voltage and resistance/capacitance. Maybe thats why some designs have a switch for multiple gain settings? If a manufacturer doesn't even mention overload margin in the specs/manual then I would stick to .25mV-.32mV on a valve stage with 66db gain, and .22mV-.32mV on a solid state one.
In my earlier post I mentioned that the description of the Ref Phono 2 at the ARC website does not indicate which gain setting the 250mv maximum input spec corresponds to. As might be expected, looking at the gain numbers and the specs for maximum output makes it clear that it only applies to the low gain setting. The maximum input for the high gain setting can be calculated based on the gain and maximum output numbers, and works out to be 15.9mv.

Good comments by the others above. I should clarify that my earlier post was just intended to address the question that was asked, about phono stage overload margins. Selection of gains which are optimal for a particular cartridge and system obviously calls other factors into play, including preventing overload of the front end circuits in the line stage, avoiding having to operate the volume control near the bottom of its range, avoiding the increase in distortion which may occur as the overload point is approached, and optimizing noise levels.

-- Al
KAB USA has a phono overload calculator along with an "ideal gain range" calculator on their website. I've used it in the past and it helped. I believe it is at the bottom of their phono stage page.