That upper rolloff in the OPT comes from a number of distributed capacitances and leakage inductances in the transformer - it will not be a simple filter. Lots of transformers have weird resonances up at the top of their range. In fact, some makers rely on a resonance to push up the bandwidth. Otherwise, I vaguely recall that a well behaved transformer has a second order rolloff up top.
Ie it's a very complex low pass filter with less predictable phsae shift. That's one guess for why the channels are not summing as you'd expect.
I would think that relying on the OPT rolloff would be detrimental to sound. The load presented to the tube up there is going to be extremely reactive and screwy. |
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