will
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So many variables...efficiency ratings, amp ratings, how different tubes effect the amp output, room size, speaker placement, source voltage, pre used, listening comfort zone, even speaker cables ... acceptable volume assumptions are a labyrinth to me!
I have a Torii MKIV (25 watt), HR-1s (rated 92.5 dB), and a "t" shaped room that is difficult to accurately calculate since there are several shallow alcoves, and also partially open segues into other spaces. So the main listening area is far from a straight up rectangle, but roughly 28x15. One end ±1/3 of the wall is open, a walkthrough and a pass through into the small kitchen. On the right, in effect part of the listening area, is a small bump-out creating about 1/2 of a small dining area, the other half in the listening area proper. And on the left is a bump-out that is an entry way to the house. The kitchen and space extensions combined add up to ±28 x 10. I guess the main listing area is a little over 400 sq ft, and with extended spaces, something like 700 sq ft.
My amp is toned back from max using 40 uF power supply caps rather than 47s, a milder than usual rectifier (4V, 1.1 amp), OB3 rather than OA3 voltage regulators, and ECC189 input tubes. Also a similar rectifier in my CSP3, if I use 5V higher amperage rectifiers, or OA3s, my setup can go louder, but I love the sound of these old mesh plate Euro tubes, and OA3s make my amp too forceful sounding for me. My speakers are in the middle of the long dimension of the listening room area (28' without the "t" extensions) and only about 5.5 feet apart. They are angled back a bit, and toed out just a little. So not maxed focus at the seat, but I prefer it that way, with great balance, space and soundstage, and it sounds great anywhere in the room, anywhere in the house for that matter.
I have a Gustard x20pro DAC, balanced outs @ 6 volts, then a ZBIT, then CSP3. This pre stage combo causes the amp to saturate at a little lower volume than with either pre stage alone. But I really like the sound tuning flexibility from gain balancing with both along with the Torii, so keep it this way.
For movies, with a milder source, and just the CSP3 and Torii in the loop, I generally come close to maxing out the Torii volume, and run the CSP3 not maxed, but on the higher side....giving good volume for my wife and I's movie immersion preferences. Fully maxed, I don't tend to get distortion with the DVD source.
But in my late night music sessions, higher source voltage, and both pre stages, though gains are set lower, my favored volume is louder, putting me close to the edge. In fact, with my test track playlist, I usually set the volume by going into distortion on hot notes on a hot recording, and then back it off a bit before listening.
Quite satisfying, it is room filling and captivating, but not ear shattering. If I could get it without sacrifices to the sound I love, I would prefer having just a little more headroom.
I have tried lower power Decware amps here, some with my MG944s which are 94dB, and, with the SE34 being good on a lot of music, but also quiet enough to feel incomplete on others, and too quiet for my preferences on a percentage of movie mixes. I really liked the sound of the speakers, so did not look into more efficient ones. This was quite a while ago, but figuring I could always use more power, I got one of the first Torii MKIIIs.
With DAC sources that are 2.25 to 6V, I have never noticed being able to get meaningful volume increase before distortion from having a pre before my Decware amps....
I can dial in more density by upping the pre stages, but it seems that if the source can drive the amp fully, the amp will distort at close the same output volume with or without a pre. I have not checked this with a meter, but this is the sense I get...more pre gain, the amps need lower attenuator settings to avoid distortion. So unless the source has low output voltage for the amp, in my experience, I have not been able to understand the concept that pres can make the Decware amps I have tried appreciably louder.
Finally, on the borderline with power for my room and setup, rather than letting "low power optimism" guide my decisions, I would try to calculate speaker efficiency, source, and amp power in relation to room conservatively, trying to be sure there is a little excess rather than potentially having to struggle with the edge.
My system, room and tastes anyway.
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