120v to 240v Adapter to power Amp in USA

DON’T DO IT !
What you want is a step-up transformer. I would try this - https://acupwr.com/
No personal experience but I read good things about them. I would get more power than required by your amp’s full power. Some say - double the power, though this particular company claims that it is not necessary with their transformers.

 Just change your wiring so it's 240 V. Very easy to do, depends how far you are from your panel.   American stoves and dryer's are at 2:40. I would guess that it might actually sound better at the higher voltage is well. 

Isn't it a step down transformer that you need?
In any case, I think inna is correct. 
B

No it's made for 240 and American is120. If you use a step up it may be starved for current. That's not the best way to do it. 

You could do it and it will work buts it's not th best way

240v just scares the crap out of me. So that’s an interesting point. I could get a double pole breaker for the panel but then I assume I will still need a plug adapter.

As far as the step up or step down, wouldn’t it be a step up since I need to go from 120v to 240v? Plus the website describes the step up as using a coffee maker from Europe in the USA.

The transformer is $165 for the 500 watt. I should either change my plan and buy something else or wait for a better deal used than is available right now. 

Can you ask the manufacturer to wire it for USA voltage when ordering?

You can't just put a double pole 20 amp breaker in the panel box and get a plug adapter. You will have to make sure the wire running to your receptacle is at least 12AWG as well as all receptacles and switches on that curcuit per code. 

Not only that everything on that circuit would then be 240 and everything on that circuit would need to be upgraded and possibly switched to a different circuit for instance if there are any light fixtures. Easiest thing if possible would be to run a seperate 240. 

Right on the running a new independent circuit with 12-2 for a 240. That’s what I would do. 

Also, Stereo5 I co reacted Atoll and they said they can be made to order with the 120v, but once they figured out I was from the USA trying to order an amp from France that costs $1000 and have it be made with 120v they wouldn’t do it. They said to go through the only distributor in the US because they don’t want to circumvent him. However, he charges $1900.

I had already paid and everything and they made the dealer from France refund my money. All amps are made to order and they wouldn’t do it even though I said I would pay extra for the 120v option. Still waiting for the refund to go through. 

The distributor in the US is super nice and knowledgeable but I don’t think overcharging because you have a monopoly is very cool. These things go for €839 all day long all over Europe. 

I do believe that you can get an outlet in your home for 240 volt.  My dryer and other large appliances were plugged into them.  I don't know if that is the same outlet needed for your amp.

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

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.

Transformer design for 50Hz has no problem work at 60Hz.

Unless you plan on keeping this amplifier forever, I'd seek a simpler solution, such as finding an amp that works with your domestic 120VAC

I agree that the best AC power would come from a directly wired 240-volt outlet. Not hard to do and there is no reason to be apprehensive of it.
With that said I totally agree with cleeds, find a good amp that works with your domestic 120 duplex outlet. There are many great amps available.
I must ask, whats so special about the Atoll amp?