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Power output of tube amps compared to solid states

I'm having a hard time trying to figure out how tube amp power output relates to solid state power output. I've been looking at the classifieds for tube amps and I see lots of tube amps with 50w or 60w output, but nothing close to the 250w output typical of solid state amps.

So I have no idea what type of tube amp is required for my set up, right now I'm using totem forests with a required power rating of 150w-200w at 8ohms. The bass is so powerful on these that I have the sub crossover set to 40hz.

My question is, are tube amps so efficient that 50w from a tube sounds like 150w from a solid state? Or will 50w output from a tube severely limit how loud I can play my speakers? If so, are tubes usually meant to be driving super-high efficiency speakers?

I had previously tried a tube pre-amp with a solid state power amp (both musical fidelity) and didn't like the results because the imaging suffered greatly, even though the music sounded nicer from a distance. Now I want to try a solid state pre-amp (bryston) with a tube power amp (no idea which brand to look at), but I don't know how much power output I need or if it will even be possible with my speakers. Does anyone know what I would require?
acrossley
atmasphere's avatar
atmasphere
11,807 posts
 
I've only seen snipets but its easy to prove if you have some very basic test equipment.

All you need is a sine/square wave generator, a small amp of any type, a VU meter and a speaker.

Set up the sine to drive the amp, which is in turn driving the speaker. Put the VU meter across the speaker terminals. Obviously you don't need a lot of power for this test. Set the sine wave to read 0VU on the meter. Now switch to the square wave and set it **without looking at the meter** to the same apparent sound pressure level.

What you will find is that with the square wave you are setting it somewhere in the neighborhood of -20 to -30 db to get the same sense of volume- less than 1/100th of the original power!

Square waves are composed of only odd-ordered harmonics. This is a very simple test, but it illustrates the issue very clearly.
unsound
7,329 posts
 
I'd be more interested in seeing at what volumes, ratios, and correlations are involved vis a vis the parameters in which the devices would be used in actual practice and what the rates of responses were and what they were compared to and against. Outside of that, the snippets might very well be taken out of context.
atmasphere's avatar
atmasphere
11,807 posts
 
Unsound, seriously, just try the test I outlined above. It will eliminate any doubts you may have. When GE did their tests they found that people would not object to up to 30% THD- if it was all 2nd harmonic. But less than 0.1% of odd orders and they objected quite a lot.
unsound
7,329 posts
 
Atmasphere, I don't have that kind of equipment. It's not that I doubt you personally, it just appears as though it might be out of context.
atmasphere's avatar
atmasphere
11,807 posts
 
Unsound, its not. Almost any service shop would have such gear though, you could easily set up this test at almost any one of them simply because the speaker and the amp really are of no consequence in the test- the results are that profound.

How the human ear detects volume is a fundamental rule of human hearing- the 5th, 7th and 9th harmonics are the cues that tell us how loud a sound is. If these cues are distorted (enhanced) even by slight amounts, we hear it. Bright, hard, sheen, clinical, brittle, etc. are all words that audiophiles use to describe enhancement of these harmonics by very slight amounts; 1/100th of a percent is easily heard.
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