So, are you saying here that you have a tube amp in your future?? :)
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I can't imagine it. ;-) But after reading your website and reading so many of your posts I wish it wasn't such a PITA to listen to what your amps, which have a design I wouldn't normally consider, would sound like compared to my Levinson amps. Unlike properly designed speaker cables, power cords, and the like, I suspect there could be audible differences, though I more strongly suspect that these differences would be coloration, not greater accuracy. Nonetheless, even a curmudgeon like me occasionally succumbs to curiosity. |
Tvad writes:
Well, I'm of the opinion that it matters based on what I've experienced in my system using speakers that had an uneven impedance curve.
Relating back to what Unsound stated in his previous post, the reduced power output into higher loads (lower impedances if I'm reading Unsound correctly) from an amp that does not double down (double power as impedance is halved) resulted in a sound that was always "bright" because less power was being delivered by into the mids and bass frequencies than the treble frequencies. Therefore, there was a higher decibel level in the highs than in the mids and bass. The difference was not large, and it probably wasn't noticeably measurable on a Radio Shack decibel meter, but the results were clearly audible on my speakers that had an uneven impedance curve.
Once I drove them with an amp that doubled down, the sound was evened out and the speakers no longer sounded "bright".
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Sorry, but this is pretty basic misunderstanding of how amplifiers work. An amp with a low output impedance does not have a frequency response that varies with a speaker's impedance. The key parameter that varies is potential current delivery by frequency before clipping occurs. So for a good voltage-source amp with 100w into 8ohms, if the speaker has a peak impedance of 16 ohms into 4KHz the amp will clip at 50w, and if the lowest impedance occurs at 40Hz with 4ohms the amp will clip at 200w, but the frequency response at 50W will still be flat (within the amp's spec) across the entire spectrum up to 50w.
Trick question - what happens if the speaker is reproducing 4KHz and 40Hz *at the same time*? |
Yes- audio equipment does not care what kind of music you play on it.
An amp with a low output impedance does not have a frequency response that varies with a speaker's impedance.
That depends on how the speaker is designed. Take a look at
http://www.atma-sphere.com/papers/paradigm_paper2.html
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Yeah, we've had this discussion before. Same old same old. Lots of assertions, but no supporting data. Negative feedback is bad because it causes time-domain distortion, distortions we can measure aren't important, and high output impedance doesn't really affect frequency response linearity. Frankly Atmasphere, your assertions remind me of Audioquest's argument that skin-effect really does matter at audio frequencies, even though all of the measurements say it's inconsequential.
I think it has been well-said previously in this thread that we don't see more high-current amps because they're very expensive to build, and because most people don't need anywhere near as much power as they think they do at low impedance levels, so very high current amps are mostly for people that have more money than sense (like me).
Tube amps are for people even more skewed towards money than sense. ;-) |
Isn't clipping an even worse consequence than unbalanced frequency response alone?
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Yes, absolutely. But unless you listen at *very* high levels (like averaging higher than 95db) most audiophile amps (100w+ per channel) with most speakers (89db sensitivity at 2.83v) probably won't clip. If you are clipping there are lots of 200w+ amps into 8ohms that will likely do you or your speakers harm before they clip.
Actually, my experience is that most audiophile speakers sound like crap at very loud levels. There are notable exceptions like Legacys, big Wilsons, and the top-of-the-line Revels, to list a few, but most don't, so I'm wondering what people think they need so much power for? I know people think they need 600w/channel into 4 ohms, and if they're willing to pay for it I say: go for it, but the math looks like you'd be producing 120db+ peaks, and I can't believe people are listening at those levels. Or am I naive? :-) |
Well, Tvad, since I assume I'm the root of your urge to leave, I think you're over-reacting. For one thing, in the interest of full disclosure, I was multitasking when I typed in that response, and while (I think) everything I said was correct I actually *misread* your post in my haste! Yes, IMO, you still have a misunderstanding about ss amps work, but I'm actually feeling pretty stupid at the moment for explaining some behavior related to what you were talking about, not the specific effect you were actually describing! Sigh.
I also admit to enjoying banter like this entirely too much, and it was never intention to chase you (or anyone else) away. So how about you stay, and I'll try to cool my responses a bit, and I'll also try to improve my focus before I type! |
Oh yeah, and a correction of my multitasking math, assuming a speaker with 89db sensitivity at 2.83v, and assuming a 4 ohm impedance, 600w/ch does not give you clip-free 120db+ peaks, you'd get about only 114db peaks or so.
Boy I'm stupid today. |
Why would I want less power? I think the better question is why would I accept less. My reasons:
1. Even 110db peaks are really, really loud. I'd like to hear for a lifetime.
2. Most audiophile speakers will have significant distortion at these volume levels. Why listen to so much distortion?
3. Most stereo solid state amps will need well over 20amps at 120v from the wall power outlet to produce 600w/ch. What are you plugging the amp into? ;-) |
Foster-9, if you're looking for used amps there's a lot of selection:
Any Krell amp. There are several Evolution 302s available, as the 302e just came out. The older FBPs are great too. Any higher power than a 300-series amp just seems like overkill to me.
Any Levinson 33x or 43x-series amp, or any later models. My one caveat with Levinson is that service can be complex and expensive. My 334s have been bullet-proof, but in current dollars remember that even the low-end 334s would likely be $10K each.
The Parasound JC-2. These have always tempted me, and they are occasionally available used. They were $3K each when they were introduced in 2003, but now they retail for $4500 each.
Bryston, Ayre, Pass Labs, Classe, Coda, Boulder... mostly North American stuff, since high current amps seem to be a largely western hemisphere thing. Of course, these are all very expensive amplifiers. For used equipment there's a good economic argument for Krell & Levinson, simply because there's an active market and these amps retain high resale values. Any of them will be costly to service.
New high-current amps that claim to double power with halved impedance seem to start in the $5K range and go up. Way up. Krell and Levinson seem to think $20K amps are mid-range nowadays. Mostly I think what we're paying for is fancy aluminum casing work and Swiss-watch-class build-quality in a North American factory. (Most of the components will be imported.)
IMHO, the most important spec for a properly design solid state amp these days (well, at least the one I look at first) is signal-to-noise ratio. Almost everyone has low distortion and high power, but noise is a different story. Most amps are rated at something like -100db below full power, and since they usually have 25-30db of gain we're talking in the range of -70db of noise, sometimes worse, below 1 watt of output, which can be audible with some speakers, especially if the frequency distribution of the noise amplitudes include a good bit of output below 20KHz. Maybe it's just me, but I find a dead-quiet background attractive. The latest Krells are very low noise, for example, the older Levinsons less so. |
Unsound, I did miss the $2K limit. That makes it difficult... and my previous post useless. ;-) |
Atmasphere threw me off with that Ayre recommendation. :-) |
Unsound says: Well Weseixas, I think we part ways on your appraisal of Class A. More often than not (but not always), I've found the more Class A the better the sound. The only problem is many so called pure Class A amps either don't have enough power for the the speakers I prefer, or the cost is beyond my budget. ...And of course, the issues of size heat, efficiency, etc..
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Is predictive bias-level adjustment a la Krell and Levinson enough, or must it be pure, brute-force Class A operation only? |
