Thank you @badpuppy. Well, the converter to 6v didn't produce any sound whatsoever.
I used this
https://www.amazon.com/gp/aw/d/B00CG...b_b_asin_title
But I see now that it is only 3 amp output max :-) so I guess I need to find another one that can output at least 6 amps, correct?