ya I was told it was the fan or something like that the signal is mint on all but the ZPA0.5 it distorts.
Links and specs here
http://www.phoenixgold.com/2004/titaniumamps.html
and here
http://www.phoenixgold.com/webfaq/ZPA.htm
EDIT: I forgot to say if you don`t know the amps they are way...