System phenomenon when playing loud

Mike and George, thank you!  Excellent thoughts.  I don’t think it’s the room, but the room is about 15’ wide (speakers are along that wall) by 25’ deep, 9’ ceiling.  No treatments on the walls (yet), outside of normal pictures and other furniture.  It’s important to note that this high frequency suck-out happens in an instant.  Not gradual at all.  And it happens in both channels simultaneously.  Thanks for asking that question!  This leads me to believe that the problem may lay in the preamp or, as George mentioned, the speakers’ crossovers.  I would have never thought of the possibility of iron core inductors getting saturated.  Thanks George!  
In any case, I’m having a wonderful time testing the outer limits of this phenomenon.  It seems that, at least in this early exploration, that this happens, once, when the system has been running, at a good substantial volume (82 on the Line 1, and I do know this is an arbitrary, subjective number, given all the components) for a longer period (about 2 hours at least this evening), the phenomenon isn’t reoccurring.  
Spoke too soon, just happened again.  It occurs in both channels simultaneously, I think it’s got to be the preamp or the inductors, not the amps, given that they are mono blocks.
dare I start digging into the Triangle’s crossovers?  Not tonight.  Too many tunes to listen too!

thanks Dudes!

Dave

Looks like they are not opposed to using iron core chokes to save some money.
These could saturate when "cranked up loud" as you put it.

http://www.hifishock.org/galleries/speakers/triangle/_cache/altea-esw-2-triangle-280x196.jpg

http://www.hifishock.org/galleries/speakers/triangle/antal-ex-2-triangle.jpg

http://www.hifishock.org/galleries/speakers/triangle/altea-ex-2-triangle.jpg

If they were mine and I experienced the same problem, I would replace them with air core chokes of the same inductance and impedance, if you can find the same, you can get something a bit higher in inductance that’s close to the same impedance and de-wind it down to the right inductance. I did the same with some Yamaha NS-1000X or was it B&W801? long time ago, and the difference was very noticeable for the better when "cranked" up loud

Cheers George

My suggestion is try a different preamp. Or, your attenuator on the SF pre might be corroded a bit, causing the problem. If you can access it easily, you could try cleaning it with some contact cleaner/enhancer.

Hope you get it fixed, regards,
Dan

Much thanks, George!  I’m imagining that the hard part will be determining the value of the inductors.  Unfortunately, in my experience, they don’t often have a handy label on them when factory installed.  
Last night as I played with volume levels, I could find the point where the phenomenon occurred, back off a bit, bring the volume back up, etc.  I discovered that the phenomenon did have a fade in/out, not quite the “flipped switch” I described earlier.  But the fade was very quick, just as I’m imagining the saturation effect might be.  
Much thanks guys!
Dave

A lot of the reasons why music becomes congested and distorted and compressed at moderate or louder levels have to do with things that go bump in the night, as your humble scribe has intimated over on the other loudness and congestion thread currently in play.

A lot of the reason are not (rpt not) related to the system per but to our perception (hearing) of the sound and the effect of the local environment on our sensory perceptions, especially the perception (hearing) of sound. You could say it’s mind-matter interaction. 🧠 It’s not physical or electronic. It occurs in the subconscious.That’s why this phenomenon occurs even when audiophiles are careful to address all of the usual (physical and electronic) suspects - you know, vibration, absorption, diffusion, break-in, fuse direction, cable direction, RF, sufficient power, time of day, etc.

“There is nothing wrong with your television set. Do not attempt to adjust the picture. ... We repeat: there is nothing wrong with your television set. You are about to participate in a great adventure.” (Outer Limits) 🤗