I just modified a Casio Rapman. It is used in a vigorous live setting (not for Rap-mastering per se) and the owner was having problems with the output jack. The Casio Rapman is a fragile and cheap thing, not really meant to be used for more than occasional, gentle, pitch-shifted raps over Japanese preset backing tracks with chorused carhorn solos. I replaced the 1/8 jack with a 1/4 female connector on the end of 10 inches of patch cable and replaced the dual pole switching of the jack with a switch on the front panel. It can now be used with an amp without an 1/8 to 1/4 converter hanging out the back cracking the jack from the board (which happened %100 of the time otherwise - the customer had run through 8 Rapmans in this fashion).
an unmodified Rap-Master
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| modified Rapman |