Power converter

If i purchase a unit from asia(230V) and can not be switch to 110V,and use it with a converter in the U.S..would it affect the sound quality in anyway?..thank
As long as it will work on 60Hz instead of 50Hz.. Most things will except turntable motors ;--)
If it is an amp, yes, sound quality will be affected. Other components less so, and digital source probably not at all.
What Nsgarch said. And if it WILL work with 60Hz, the stepdown device has a good chance of improving the sound. A simple transformer is best (with no extra conditioning or regulation). Make sure it has some overcapacity so there is no chance of core saturation. In the case of a power amp, three or four times overcapacity is good, less for a preamp or CDP.

A friend of my teenage son's was over last night. I had just bought another transformer and he wanted to know why, so we did a demo with and without my current device.

It had been a while since I myself had done a comparison. We listened to 7 minutes of the Mork/Brown Haydn cello concerto #1 on Virgin, first without, then with my isolation transformer. For the young man, an audio neophyte, there was an enormous difference in soundstage, timbre, detail. For me too!
I am sure Arni's experience has been as he describes. However for me, using
an isolation transformer on seven different digital sources to date has in
every case transformed the sound, improving it immensely in my view.

Those sources were: Philips 921, Cambridge CD4, NAD 541, JAS Audio Musik
1.2, Shanling CD-T100, TEAC VRDS T1, Esoteric P-10. The transformers were
from Hammond, Triad, Topaz and Deltec.

I hypothesize that the AC power is impure :oP in both areas where I have tried
the experiment (city and country).
Thank you for all the iput..The piece I want to purchase is the pre-amp,and according to the manufacture.It can not be convert to 110V,unless the transformer is change.I guess I have to use a power coverter from 110V to 230V in order to use it in the U.S..I am not sure if this is a good idea or not.
As long as your converter can handle two or three times the preamp's current draw it will work fine. (Preamps don't draw a lot of current anyway.) And not only will it work fine, it will almost certainly sound better than it would with a 230V supply and no transformer.

Check your preamp's back panel (or ask the manufacturer) for its rated power draw, triple that and look for a transformer with around that rating.