Comparing Phono Pre-Amps

     You could use something like this, probably:

https://www.amazon.com/Switch-Passive-selector-switcher-Splitter/dp/B0894TGBT8

   Maybe two (they're cheap).   One (connected backwards) for selecting which phono preamp the TT’s signal feeds and the second to choose which phono pre feeds your line stage.

This might work — hook the input pair to your turntable and the other two output pairs to your two phono preamps.  Hook each phono pre to a different input on your stereo preamp and just switch inputs to compare the two phono pres.  You obviously need two pairs of stereo interconnects to hook up both phono preamps to your stereo preamp, but you might have those on hand and if not they’re obviously easy to find.  Best of luck. 
https://www.amazon.com/Wv-rcato2-rcakite-05-Stereo-Output-Splitter/dp/B013JO0CGU/ref=sr_1_3?gclid=EAIaIQobChMI6ae80oXQ_QIVZjizAB3QnAeKEAAYASAAEgIKCPD_BwE&hvadid=282779888790&hvdev=c&hvlocphy=9004289&hvnetw=g&hvqmt=e&hvrand=9117936897464617218&hvtargid=kwd-483056781576&hydadcr=18920_9699079&keywords=rca+splitter+2+male+to+4+male&qid=1678406024&sr=8-3

I wouldn’t recommend splitters. They may introduce more uncertainty into the equation. 

I want to reinforce the idea of long comparisons. A few quick swaps will tell you if there are any huge tonal differences or detail differences. But long… I recommend at least a week listening to music (not the system)… two is better auditions… then switch. This will allow you to understand the sound much more deeply and make the comparison. Typically, taking a lessor component out is where the real moment of understanding comes.

Thanks for the suggestions.

I think I might try the cable route.

For the ground, can I simply send the ground to each phono-preamp or just to 1 one of them?

This really is just for comparison reasons not a permanent solution.

Thnx

+1 @ghdprentice but I also understand the OP’s desire to do quick A/B comparisons.  IME they can both be beneficial.  As a reviewer I used to start with quicker A/B comparisons just to point me to areas of difference I should pay attention to and then listen for those things during longer listening sessions over multiple genres of music to validate and nail my impressions down.  I found this to be an efficient, valid, and effective way to compare components, and as a reviewer you have limited time so anything that helps.  But that’s me, and everyone works and hears differently so find what works for you and just do it is what I’d say.  I know the inexpensive splitter I recommended is likely not optimal, but for 27 bucks it’s sure an easy and low-risk avenue to try, and if it happens to provide the OP with insightful info it could still be very valuable, especially if the quick comparison impressions coincide with longer-term listening impressions.  Just my $0.02 FWIW. 

+2 @ghdprentice 

I basically no longer do A/B tests.  I prefer to listen for long enough to something that I have a good sense of its sound.  Then listen to the other thing.  If changes are not obvious with that type of listening, I am no longer convinced they are all that important.

Regarding the use of any type of switching device, I would not want to assume that it has no effect on the cartridge loading.  I think you want to go straight from tonearm to phono stage.

Splitters may not be the ideal connection, but they are good enough to hear differences.

Like/prefer it? keep it? return it? 

friend brought his new tube phono to compare to my tube McIntosh mx110z's phono.

TT to splitter

splitter a. to his new tube phono, then to integrated amp 'AUX'.

splitter b. to my SUT, sut output to mx110z mm phono in/preamp out to integrated amp 'CD'.

switch integrated inputs 'CD' to 'AUX', instant comparison.

NOTE: volume differences might have to be dealt with. In my case, I was able to adjust the mx110z's volume to match the volume of his into AUX. Sometimes it is just a temporary pencil mark.

In my case, 3 arms into/trru SUT with 3 inputs and PASS for MM, we were able to compare MC; MM and MONO MM. I needed to adjust volume for their differences.

Yes, any of those switches, typically old video switches, 1 in, 3 out can be used backwards, 3 in/1 out. 

You still need to solve volume differences.

Thanks for the suggestions.

I like the idea of doing quick comparisons and then taking that information to do more long term listening and narrow down what I really like.

There is a company that makes high quality signal routers - Mapletree Audio. You can have them configure one however you want it or you can go with the standard 3 in & 3 out.

This is the best solution IMO if you want to compare phono preamps. You can have both hooked up and you can switch at will. I personally prefer short term switching because I know from experience that my system can sound better or worse on different days without changing anything (I think the difference lies within myself as opposed to external forces). I will usually pick a single track, play the track all the way through, and then play it again through the other component. I also like to play a short section, maybe 10 seconds, of a track that represents a particular sonic characteristic. Being able to rapidly switch facilitates a good comparison. I will do this over a couple weeks at different times because I know that my hearing acuity is not always the same. I'm distrustful of changing out a piece of gear and listening for a few weeks because researchers have demonstrated that audio memory is very poor after a short period. It's a golden opportunity for expectation bias and confirmation bias to set in.

Long listening sessions are a good method.  However, if A/B switching is desired too, then use two turntables to do quick switch A/B listening.  Many of us have more than one turntable.

Of course the tables will not sound the same, but differences can be noted from the A/B listening, then swap the turntables into the phono preamps and listen to what differences switch or persist.  This would help extract differences attributable to the turntables vs the phono preamps.

Cartridge loading has to be considered! By loading alone, the same cartridge can sound different with different phono sections, owing to things like input capacitance and high frequency overload margins.

So an AB comparison using a switch at the input will not produce accurate results, unless the correct cartridge loading is introduced as well.

High output MM cartridges need loading because their inductance is so high that when put in parallel with the capacitance of the cable, a resonance can occur at the upper end of the audio band or just beyond it. This can cause overload problems which can result in brightness as well as ticks and pops as the front end of the phono section overloads. It can also cause brightness because the resonance acts as a tone control.

LOMC cartridges have far less inductance, so the resulting resonance so high that it acts as Radio Frequency Interference (RFI) being injected into the input of the phono section. This is why some phono sections for LOMC cartridges have loading switches, not for the cartridge so much as it detunes the resonance, preventing the RFI and the brightness it can cause. However, some phono sections are designed by people that know this phenomena occurs and so don't need any cartridge loading at all. So the LOMC cartridge might sound bright on one phono section and not on the other, although when loaded the bright phono section might sound just fine.

Well I ordered the Schitt Sys.

I will see how that works out.