Dropping 20V to 17V AC - Resistor?

[SmokeMonster]

I need to drop 20V (4A) AC to 17-18V, and from what I've read a 1ohm 10 to 15-watt resistor should work. Is this a good idea?

I'm using it for powering a Q-Sound amp. I bought an 18V 4A AC rated power supply but it actually outputs 20V. This is above the amp's max threshold which causes it to not output sound.

 

[SmokeMonster]

Never mind. I used a variac to drop the line voltage, lowering the 20V transformer's output to 17V. Still nothing. It must be dead.