Shrill high frequencies

Tell us about the rest of your system.

Did you allow enough ‘break-in’ hours? Also, experiment with PC feeding the IsoTek. 

+1 lalitk

Amp is Luxman MQ-88UC, preamp Audible Illusions Modulus 3b factory upgraded, sources Modwright modified Sony HAP Z1ES,.Magnum Dynalab MB 108 tuner. All IC cables are Cardas Clear , Speaker cables Nordost Frey 2. Speakers are KEF LS 50 or Goldenear Triton 1, subs REL Stentors. 

Magnum Dynalab MD 108 tuner, Modwright modified Sony HAP Z1ES, Audible Illusions Modulus 3A with all factory upgrades, either an Atma-Sphere S-30 mk 3.3 or Luxman MQ-88UC amp KEF LS 50 speakers 2 REL Stentor subs. ICs are all Cardas Clear, speaker cables Nordost Frey 2, power cords Shunyata. 

At your suggestion I changed the power cord from that provided to Shunyata Delta. No joy. Maybe break-in time will help. 

Maybe the Isotek needs more break-in time. 

BTW - I use a MD 108T + KEF LS50 and those 2 are definitely not bright. My Accuphase T-101 tuner is much brighter than the MD 108T

I have the Isotek sigmas unit.  I did a power cable shoot out with my amp, and found that Shunyata cables did not like being plugged into the Isotek.  Especially the NR versions.  Although I did not have issues with high frequencies, in my case it was a tonality issue.  I plugged the amp directly into the wall.  Even with other PCs, I recommend trying plugging the amp into the wall.  

Try MIT or Transparent cables and IC's instead of the Cardas/Nordost Frey. That should do it.

Matt

Did you try the Isotek PC that came with the unit?  I too have a Sigmas and have noticed no brightness at all.  I use a Synchro with it, but a regular PC would be fine.

The solution was to plug the Isotek into an Audioquest Power line 2 with a Nordost QRT inserted.

Thanks to all for sharing your mighty brains and happy listening!