Can I convert stereo to mono for a phono input

Erik, keep in mind, though, that with the meter connected as you described it would read the difference between the two channels, not the sum. Your suggestion would work, when playing an out of phase track, if the connections to the two cartridge pins for one channel were interchanged. Although if that were done I would wonder if the proper connections could subsequently be restored without physically affecting the adjustment to some degree.

Regarding mb1audio's question, yes of course that would provide a mono signal, but I would wonder if the corresponding lateral movement of the stylus would allow as precise an adjustment of azimuth as the vertical movement that occurs while playing an out of phase track would allow. Maybe it would and maybe it wouldn't; I'm just not sure.

If the preamp or phono stage has a relatively high output impedance I suppose it would be reasonable to simply sum its L and R outputs together with a y-adapter. But I would be hesitant to do that if it has particularly low output impedance, especially for a significant length of time, at least without getting an ok from the designer.  The resulting current flow between the output stages could conceivably be more than they were designed to handle safely.

I suppose the best approach might be to purchase an inexpensive pro-oriented mixer, and connect it to the outputs of the preamp or phono stage. B&H Photo/Video (bhphotovideo.com) sells many such devices.

Regards,
-- Al
 

A combination of these y adapters will accomplish what you want to do.
http://www.audioadvisor.com/ssearch.asp?txtsearch=y+adapter

Azimuth adjustment on a test record like Analogue Productions, provides a test tone for each channel individually. No need to build or buy anything other than the right record.

Ops! You are right. You need the maximum AC voltage!! :) Same connection. My bad.

Best,

Erik

It remains a little odd to me that Phonograph cartridges which are inherently balanced devices, don't have XLR outputs.