Steve Deckert
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UPDATE: MORE LISTENING TESTS
I had an interesting evening with the TORII MK IV last night. I played it on my corner horns, which for that amplifier are a worse case scenario when it comes to bass at high volumes. Since the amp likes to put out more current into higher impedances, horns of this design can get a touch boomy.
This very tendency of the amplifier to sound boomy on the corner horns makes the other 12 pair of speakers in our listening room sound better than they actually are… but nevertheless, it is the worse case scenario you have to design for, so on we marched for the next four hours with the MK IV on the corner horns.
The new MK IV bass switch really alleviates this tendency with these speakers, so it was of course on the entire time. And after shifting to more demeaning material, the positive feedback switch was turned off, dropping the dynamics slightly and allowing me to crank the amp a bit harder. Then during the acid test, I used electronic music which has wall cracking low bass at high SPL due to massive compression, I even switched speaker taps with the speaker impedance switch to the softer setting. These three adjustments kept things tight and clean as the evening matured and the material continued to get more and more challenging.
It is interesting to note, that after four hours I gave up on the EL34's and installed the KT66's that I designed the MK IV to favor. The TORII's tendency to get a little over the top on these speakers had now disappeared and the amplifier became as linear as if there were feedback applied. The midrange and top end and bottom end are virtually perfect now, and at any volume. Nothing changes from modest volumes to louder playback levels and there is a very apparent increase in overall headroom and power.
Naturally, this was a real thrill as I was well into hour five and playing my challenging tracks to see how well the amplifier maintains it's usable power. Suddenly this simple tube change made everything twice as good, and I realized I didn't need the speaker impedance switch on the softer setting anymore… so I switched it back and everything got 3dB louder, even fuller, much deeper, and without a trace of strain. It was truly a wow moment…
Things are getting really fun now… so sucked into the recordings with this latest bust of flavor, another hour went by and I realized I didn't need the bass tighten switch on, so I turned it off. Everything was still fine, nice and tight, but now suddenly even deeper. Again not a hint of strain. It was wow moment no. 2, and I have to say that things are getting amazingly loud without sounding bad… quite the opposite in fact. (this is btw the epitome of usable power).
Another half hour went by and I realized I hadn't turned on the positive feedback switches yet. So, without further ado, I just turned them on. This was more like a holy-crap movement where I just stood there in the sweet spot of my horns in disbelief at the presence… not to mention the room shifting dynamics that simply felt real.
Ratcheting the performance and sound up three times like that I'd have to equate the experience to a drag race, where you come out of the gate with a nice wheel stand, wind it out and then hit second gear followed by a nice long pull and then hit third gear. You get a little sideways for a moment with the meat on your face pulling back toward your ears from the aggressive pull until everything is a blur… and you then float into your out of body experience. So, clearly the TORII MK IV is a competent space ship like it's predecessors all were, but this one has gears!
Moral of the story, Tungsol KT66 = MK IV… Just do it.
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