amp via transformer 220 - 110 a good idea?

IF the transformer is big enough to handle twice the current draw of the amp (more wouldn't hurt) and of reasonable quality, you should notice no degradation in its sound. As a side benefit, you might well get extra noise reduction--useful if your AC line carries a lot of crud.

Semi, you had disappointing results but you don't say anything about the transformer setup you were using. What was its power rating ( in VA, which are more or less equivalent to watts ), and its make ? How much power did your amp draw ?

Malickia, Pauly suggests you use a tranny 10 times too big. I wouldn't go quite so far--I would be comfortable with 3 times oversize and I would be willing to try 2 times--but 10 times oversize ( heavy ! ) would certainly do no harm. The idea is to make sure the transformer's iron core will never saturate and limit current.

The best transformers use oversize cores anyway; my two Topaz ultra-isolators weigh twice as much ( for their power rating ) as the others I use in my second system.

For more info about iso transformers, look for posts in the archives by Sean and Lak.