Originally Posted by Stereojeff
Your system sounded different when driven by Prometheus because it had very different frequency response. The Citadel 1.5's with no global feedback had a very high output impedance. Thus every speaker they drove had an unintended active equalizer in series with the output. Prometheus has extremely low output impedance and minimum frequency interaction with the load.
From my experience it's also true that N-Core amps, at least as designed by Morris/ATI, sound more dynamic than most other amplifiers.
It's also true that you were the first Theta customer to notice the differences.
In all fairness I received the very first two Prometheus out of the factory - and within a day or two realized how outstanding they sounded, somewhat different and I thought better than the Citadel 1.5s, so I quickly ordered three more to replace my three Enterprises at center and surround!
Regarding what you are saying re frequency response, makes total sense! The improvement I heard was hardly just frequency response, but 3D imaging was more real and more like a live concert in an excellent sonic venue!
These days, if I change out any components, aside from using room correction measurements (Dirac with my prior Theta CBIVA SSP, Optimizer with my current Trinnov Altitude 32), I also use my ears with this test disc with frequency test tones from low to the very highest: https://www.highresaudio.com/en/albu...es-system-test
Interesting is that using that test disc, with my prior Theta CBIVA SSP, I could hear 8 kHz clearly, and 10 kHz maybe 50%, nothing above (last March when I reinserted CB for 10 days or so as my new Trinnov SSP was in for a minor repair and addng channels); whereas with the Trinnov SSP I can hear up to 12 kHz clearly but nothing beyond. I wonder does this also have to do with output impedance?