Why Would a Turntable Need More than 1 Arm ?

Is the use of a Mono/Stereo switch on a preamp/phono stage as effective an alternative to an arm (be it the first or a second arm) mounted with a mono cart/stylus. Is there any trade-off to doing it this way? Is the result the same? Thanks, bird

One arm to play the record and a second arm to flip it over.

Many of my customers have more than 1 cartridge.

A single table with dual arms saves space and offers a degree of flexibility not found in a single arm configuration for the hobbyist who wants to experiment with different tonearm/cartridge combinations.

Dealer disclaimer.

or why a phono stage has more than one input or why a preamp needs so many inputs? "Elementary" Watson said.

Birdliver: a mono cartridge will give better results than summing the 2 channels of a stereo one but the switch is worth using if you have one. The mono is doing the job it was intended to do while the stereo cartridge will have movement in a plane that does not exist on mono records, it will work but not as well. Also added complexity is always best avoided, i.e. single channel to stereo signal back to mono.