How to use 100 volt Japanese audio on 110 US ?

Will Japanese built audio equipment work with no step down transformer on 110 home outlets?
some would say yes, i would say that it's best to use a step-down to ensure proper operating parameters and therefore optimum performance and longevity. i have an original japanese market component (preamp) that became significanly cooler after purchasing a step-down transformer.
it will work, but you don't want to do that. Why? you'll end up frying your equipment sooner or later. it is just a matter of time. I have a lot of equipment that runs in 100V so I ended up buying step down transformers to feed my audio equipment with the proper voltage.
just to illustrate what kind of damage you can do to your equipment if you plug it directly into 110v: I had an amp sitting in my room that runs with 100v and was plugged into 110V. someone left it on (someone must have kicked the power switch by accident or something) for four days while I was out of town. when I came back i noticed my room was hot as a sauna and I noticed the amp had been on for a long time. I turned it off and waited a couple of days. I decided to plug it into the step down transformer to test it. it did power up ok, but whenever I tried turning the volume up using the preamp the amp would go into protection mode. it wouldn't play louder than 2 on the volume knob. i guess some capacitor was fried or something. most pieces have a tolerate plus or minus 8volts give or take. put you have to remember that if you get a spike that raises the electrical power to 140V (I've seen that a lot in california) think what that would do to your 100v equipment.
get the step down transformers. try getting one that doesn't hum too loud when you plug it in. some are known for being very noisy.
Careful! If you're buying "gray market" equipment, [bought in one country to use in another] your warranty is voidable with many manufacturers.