Comparing Phono Pre-Amps

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.