Oh yeah, I figured it would probably sound terrible without a cabinet IR after it (much like any type of signal with any overdrive), or just bland and boring if set to lower levels with no power tube distortion. But since I like experimenting with my own collection of speaker IRs, I think it would be a pretty neat way to model the power amp's effect on frequency response (even if it is just a static snapshot) and would be a pretty unique use for an IR. The only similar use I can think of is some IRs floating around that somebody made with a Tube Screamer set up as a clean boost (to get the mid hump/low cut EQ curve via the impulse response rather than approximating it with an EQ plugin). I think it would be especially neat for adding presence and depth to a preamp signal by making IRs with the presence controls tweaked and the deep switch on. I'd imagine it would sound wonky by itself but good make for an awesome piece of the puzzle if used directly after a preamp signal, and in series right before a cabinet IR.
I'm actually not using a Helix or any other modeler at the moment, just stumbled upon this post when searching for IRs in general. I like to use rack preamps, then power amp simulation plugins, and then cabinet simulation plugins (IR loaders). I just think it would be really cool to replace the power amp simulation plugin with power amp frequency response IRs and see how that works. I know that the response is determined by the impedance curve that results from the interaction between the power amp and the real world speakers, and that a load box may react differently and plus many speaker IRs already have the impedance curve 'baked into' the file by creating them with tube power amps with relatively high output impedance (compared to solid state power amps), so it would be a double-dose of power amp influence when using IRs like that, but I still think it would be a really neat experiment and fun to play around with. :) I know that the RedWirez IRs are created with a solid-state power amp, so it would be a cool alternative to their impedance curve IRs that they provide for blending purposes.
Thanks for the links, I'll definitely download those and give them a shot! If you ever do decide to capture just the power amp, I'd be stoked to download the results!
