My New Magnepan 1.7i's sound dull and lifeless on the top end...why?


First time Magnepan owner - 5  days old 100+ burn-in hours on them
Associated Equipment:
-Denafrips Terminator Plus
-Holo Audio May KTE version
-Pass Labs X22 Pre-amp
-PrimaLuna EVO 400 Pre-amp
-Pass Labs XA100.8 Monos
-PrimaLuna EVO 400 Monos
-AntiCables interconnects and speaker cables
-Stock tweeter attenuator jumper replaced with AntiCables level 5 spade jumpers on the 1.7i's

My spectrum analyzer indicates both speakers highs are falling off beginning at 1.25K and are 9db down from 2.5K on
Been playing around with speaker placement and room treatments for 2 days now without any remediation. What am I missing? Suggestions appreciated.
128x128nayls02
kingbarbuda289 posts07-28-2021 8:45pmI have a pair of 1.7is. I recommend until you are very familiar with the Maggies and sort this issue out, that you run them only on solid state equipment. I have not looked up the specs on those Pass Labs monoblocks. But I would use those and the Pass Labs solid state preamp. I would put back in the stock steel plate jumper for now. Also check the fuses to make sure they aren’t blown. Make sure all your cable connections are good ones. Play music that is well recorded. Examples would be Steely Dan Aja and Goucho. If there still is a problem call Magnepan. Normally the highs aren’t as big an issue as the lack of bass impact. When yiu get this sorted there are other modifications that would make a difference.

Yes, the Pass gear sounds better than the PrimaLuna for sure. I'm not lacking any bass. In fact the base is what i'm most impressed with. I called Magnepan this morning. Still awaiting a response. Thx.
You’ve had these Magnepans for 5 days.  (I’ve been listening to Magnepans, almost exclusively for 40 years.). What speakers were you listening to before the Manepans?  Could it be that you (your ears/brain) had become used to unnaturally bright tweeters and the more natural tonal balance of the Maggie sounds dull?  ( Of course, this argument doesn’t account for your measurements. When it comes to  the pleasure of listening to recorded music, I place more importance on my own subjective aural experience than I do on measurements.)
Maggies are very sensitive to positioning.  You might try them with the tweeters on the inside and tilted towards you.  Just put CD cases behind the back legs.  Make sure they are several feet from the rear wall and try various angles.  But in general, you shouldn't be seeing that kind of rolloff on the top end so it is possible something is defective with the tweeters.
Have you checked the working of your spectrum analyser with different speakers?
Agreed with a few others,try the stock jumper. 
I use stock Maggie 1.7i, PrimaLuna tube preamp, SS Bel Canto monoblocks, and highs sound great. (Have not, however, done a freq analysis)