Thanks everyone for your answers. Your comments are very helpful. Now IŽll wait for the PSR s900 to arrive to the store and IŽll try it, then IŽll negotiate the price of my PSR 1500 and see how much I have to pay. If I buy the s900, next year IŽll buy a Korg for my collection.
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Victor

Korg Pa3x 61 - Mediastation X76 - Yamaha Psr s900 - Korg Tr61 - Roland PK5A - NanoKontrol - Ensoniq SQ1 - Yamaha D85 organ