Need to use my 220v preamp in 240v.

You will need to use a transformer. Two choices, you can use a cheaper autotransformer or an isolation transformer.

Step down the voltage at the existing wall outlet from the nominal 240V to 220V.

If you are thinking about using the existing 240V circuit to feed the 220V preamp you need to check the unloaded as well as loaded voltage at the 240, nominal voltage, mains at the electrical panel.

In the USA the voltage can range anywhere from 220V to as high as 250V RMS.
Don't know about Malaysia. How stable is your electrical power?

Your 220V preamp X 10% RMS over voltage = 242V RMS....
You could check with the manufacture for the max RMS voltage that the preamp will accept without causing damage to the unit. The preamp may even have primary winding taps for the higher voltage.
.

How DIY do you feel? For sizing, double the current draw of the preamp.

http://www.signaltransformer.com/sites/all/pdf/DU-SU.pdf

Don't know of any encapsulated transformers for this application.

Will their be an issue w/ 50hz vs 60hz?
Malaysia is 50hz.....

10-30-11: Magfan
Will their be an issue w/ 50hz vs 60hz?
Malaysia is 50hz.....

Yes,this has to be taken into concideration.

The preamp is fine at 50 Hz or 60 Hz. A transformer has to be rated for that.

Another detail ...
http://www.hammondmfg.com/dwg14d.htm

And if you want to get creative and be the first on the block ...
http://www.geocities.ws/jonrisch/catch2.htm