120v to 240v Adapter to power Amp in USA

What you need is a voltage step up/down transformer/converter
https://www.amazon.com/dp/B06VVXN2SR/ref=psdc_10967761_t1_B00FHIF8KC

A cheap adapter is never going to provide enough current for an amplifier. The way is to use the natural 240 in your home or apartment. Plenty of 240 appliances. Particularly air conditioners. In my apartment are two 240 appliances. The stove and the air conditioner. I even have a pair of 20 amp breakers which could easily be converted to 240V no problem, hardly any hassle.I suggest you get an electrician to install a 240 receptacle, plus new breaker into a spot where you now have 120v (you could even do both if there is a two duplex receptacle pair. one 240, one 120.The plugs are very different, so no chance of plugging a 120v into the 240v.)

That's another option, sure, but if $165 for a transformer is too much then paying electrician may be no less or more. Besides, what if he doesn't like the amp and sell it in a month ? Transformer might somewhat degrade the sound... 
What about the frequency of those 240 V circuits ? Does it matter for that particular amp ?

Yeah I think a whole circuit is a bit much. I would probably just do a transformer but I’m not sure if it presents a fire hazard to leave it on all of the time. 

Im starting to think maybe I should just stick with a 120v amp and call France again tomorrow and ask why I haven’t seen the Paypal refund hit yet. 

Find out what the amp actually requires, both voltage and frequency. We use 60hz here in the U.S., many European countries are 50hz, I believe. Then consult an electrician. Many of the responses here are guesses, and wrong ones at that.