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Actually, come to think of it, the idea behind THX sounds a lot like servo subs: The amp inside a servo sub sends a correction signal once it detects over-excursion/distortion, THX seems to do the same, just with headphones.
Question is, in survo subs you have built in circuits attached to the woofer cone that sends information about woofer movement but you don't have any of that in a headphone. If you don't even know how the diaphragm's moving how can you send a correction signal?
bingo. "Give the boy a prize"
A current dependent correction signal can be used instead of an amplitude dependent correction signal.
I doubt this is what they actually did. Whatever they said... it just doesn't add up. A feed-forward non-LTI filter to minimize noise was used successfully by Bob Carver, but only in subwoofers using this sort of power supply.
The "suck factor" of this amp would be off the charts if it were just some variant of a subwoofer amp slapped into a headphone amp chassis.
THX AAA uses real-time feed-forward voltage combined with feedback voltage, all in the electronic domain inside the amplifier. It works with all headphone transducers, no matter the impedance or reactance.
THX AAA was invented by THX's R&D division initially for high end pro cinema applications, and has nothing to do with any certified product or subwoofer amp. That's a completely different world.
So the feedback is passive, not active?
Hi @Bobthedespot. If you mean to ask is there electronic circuitry in series with the feedback path, then the answer is no. This is extremely well-behaved feedback (and feed-forward).
Thanks for the clarification Andrew. Quick question: Is there a fuse somewhere inside the machine or is it in the power supply? (damn me and my fuse rolling fetish)
Hi @hohsis . There's a time-lag fuse inside. 1206 size. Designator F1. Bel Fuse 0685T2000-01. It's sized to only blow if something has failed catastrophically inside. The pads are definitely kludge-sized if that's your bag, but of course I have to CYA and officially don't recommend altering the unit. :D