It appears (correct me if I'm wrong) that you went from a passive preamp to an active model. Passives are, well, "passive" and should have no inherent "hiss," while all actives have some degree of hiss, some more than others, but if it's a modern unit then the hiss should only be heard with your ear close to the speaker. This is normal.
Probably only way to "get rid of the hiss" would be to go back to a passive preamp... If the hiss is loud, meaning you can hear it at your listening seat, or is louder in one channel than the other, then you may have a problem with the preamp that would require servicing.
Probably only way to "get rid of the hiss" would be to go back to a passive preamp... If the hiss is loud, meaning you can hear it at your listening seat, or is louder in one channel than the other, then you may have a problem with the preamp that would require servicing.