Voltage drop on a rheobus?

Just bought a Sunbeam rheobus and hooked my Delta 80x38 SHE screamer to it. I noticed a considerable RPM drop, even at max position:

~4600 RPM on a rheo
~5050 RMP without it.

Does it mean that Sunbeam is a POS? Or something is to be done? I'd really like to regulate my "jet", but i want him to reach its max when needed...

how can u deal with that noise man?

the only thing i can think of is that the rheobus is only allowing you to turn it up to 4500 rpm...and it thinks thats the limit of all fans...(obviously not)....so it only permits to to go that high...try sending that bus back and getting the nexus or one with a bigger name brand..i don't htink ive ever even heard of sunbeam myself.

Hmmm... Sunbeam is not the last brand of rheobuses, and the only one having 20W per channel - I do need a serious power to handle my Delta...