Flat speaker sound/preamp the culprit?/external EQ needed?


Hi, I have a Rogue Audio tube amp, which I love, a U-Turn turntable and an NAD phono preamp. Here's my issue: on many recordings the bass can really drown out the rest of the record. In general things sound muddy. When I plug my iPhone directly into the amp, I dont have this problem. So I think the premp is the culprit. (It has no EQ controls.) Can someone recommend a reasonably priced solution to this? An external EQ? Something else? (Someone recommended a Schiit Loki.) Many thanks in advance!
ineedhelpwithcables
Is your NAD phono pre plugged into the AUX inputs or the PHONO inputs?

Ouch. That could be it. Line level into a phono stage would overload a lot and be truly awful. But I would hope he would not go out and buy a phono stage if he already has one... and then connect them together??!
"...But I would hope he would not go out and buy a phono stage if he already has one... and then connect them together??! ..."

It would not be the first time it was done.
I laugh at your comments @millercarbon but I'm not proud of it.  You are a sarcastic devil. LOL
Check your tracking weight. My guess is that the UTurn is picking up acoustic and situational feedback as others have stated. Try putting it on a paving slab. You could also add $30 Nobsound springs under the paving slab.
thanks for the comments all. i plugged the preamp into the aux input instead of phono and that has not made a difference. in response to one question, the only volume control is on the amp, not the preamp. 
if the problem is the low-cost preamp, does anyone have recommendations for a diff one? 
as for speaker placement, if that was the issue, wouldnt i hear it when i play the iphone too?