is a step up/down electric transformer bad ?

The rule of thumb is that the transformer be rated for double the maximum that you are going to ask of it. If you go above that, the transformer will add distortion to the AC line and the results are both audible and measurable! and not good.

I use isolation or center-tapped (balanced), step-down transformers on almost all my gear, all rated for 115V, including sources and 2 class A monoblocks. The exception being a dedicated, class AB, bass amp. The current swings for the latter 4X400W amp would be tough, but not impossible, to keep up with but since everything else was isolated, it wasn't necessary. Even had a regulated (ferroresonant) iso tranny for the plasma TV for a while but it was too noisy.

The only sonic difference, as compared to wall outlet, should be less noise. If there is a change in the "character" of the sound, something might be wrong either way.

Kashimura TI-19 Transformer is okay.But it is made in China.Nissyo and Sanyo Transformers are made in Japan.Only works 115V to 100v.If you want to change your Luxman L590 to North American 115V.Send me a email.

thanks all for responding. i just got upset because i talked to a luxman dealer and he told me i made a big mistake buying it like this with a transformer. so far i have been really happy with the amp. didn't detect any weird noise but it is always hard to know without comparing. the dealer told me that if i want to modify it to US standard it will cost a huge amount...honestly i may have to move in Europe so i would have to mod it again. if the is a better transformer i can maybe consider it. this one is the one they sell at Audiocube.

Ralph,
When you say "if you go above that, the transformer will ad distortion to the AC line and the results are both audible and measurable! and not good"...

Do you mean if your device draws 120W max vs your 200W transformer? Or if your device draws only 100W vs your 1500W transformer?

I admit to not having followed you through the forest...

If the latter, can you explain why that would be the case?