Can I convert stereo to mono for a phono input


My preamp doesn't have a switch to convert stereo to mono.  I would like to switch a stereo signal to mono to set my cartridge azimuth (when using two channels out of phase, this method allows accurate balancing of the channels).  Is there a way to build a simple converter: two RCA female plugs taking a stereo signal and mixing it to mono, output as two RCA male plugs (mono signal)?


I have a test LP that provides a stereo track (test signal) with the two sides out of phase.  All I would need to do is feed that through the mono converter to set my azimuth. 

Thanks for any advice.  Peter

peter_s
Lew.  The fact that the meters register differently when I switch the leads to the phone a preamp shows that it is not the meters. As for the signal, it is a test tone on a analog test record, I would think it is good, and I noticed this with multiple  recordings sources  during the process of recording.  I am away from home, but I need to look more closely at the meters to see what degree of resolution they have.
Peter, Sorry for being so pedantic and possibly condescending.  I am sure you know what's up much better than I do, since you've got the stuff in front of you.  I speak as someone who endured for several years an evident channel imbalance (L>R) in my main listening room.  I never was able to figure it out.  Then one day I closed both halves of a large double door that connects the listening room (our living room) to the adjacent dining room.  Lo and behold, the perceived (by everyone) L channel bias went away.  Sometimes it's the room.  But in your case, you say you DON'T hear a problem; you're worried about what the meters tell you.  A certain old Borscht Belt comedian would say, "don't look at the meters".

It remains a little odd to me that Phonograph cartridges which are inherently balanced devices, don't have XLR outputs.
Some do (well, some **arms** do anyway). Most tone arms have a balanced connection somewhere (even a lowly BSR or Garrard); its just not got the XLR connector.
Just play a mono LP with your stereo cartridge. For a long time, I used a stereo cartridge for everything. One time I was playing a mono Prestige repress of a Miles Davis album. I was sitting in the sweet spot, and the soundstage was emerging from the left wall, 90 deg. left of the speakers. 

My headshell has azimuth alignment, so I got out a bubble level and set it. Sure enough, the mono image returned to the phantom center channel where it belonged.

I also used a mono version of Sgt Pepper's "A Little Help from my Friends" to adjust the phase and crossover settings on my dual subwoofers. Paul's melodic bass line on that song dances back and forth above and below my 50 Hz crossover point, and having the same signal go to each subwoofer (one at a time) dialed in a seamless response that also eliminated a 100-200 Hz "hump".

Mono albums played w/stereo carts can be great tools for dialing in stereo image and phase issues.