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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
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shadorne
7,477 posts
 
Another way to think of damping is that a high damping amp "shorts" the speaker woofer voice coil when the signal is "zero" - this means that the voice coil current is maximized (sees least resistance) in response to the movement of the coil through the magnetic field which creates the strongest possible back emf which opposes the coil movement and acts as a "damper" for as long as it takes the coil to come to rest. The more powerful the magnetic field (magnet size/weight) and the bigger the diameter of the voice coil and lighter the cone weight then the better an amplifier is able to tightly control a woofer. (This is why large 4 inch voice coils that are very short (light weight) and sit in a long powerful magnet gap are so desirable. These are extremely expensive as well with a quality 12 inch woofer costing around $1000 and weighing about 25 lbs or more.

Of course at resonance, the impedance of the voice coil rises and electrical damping is not as powerful and that is where the "acoustic suspension" design becomes critical to how the speaker will sound.
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shadorne
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These are extremely expensive as well with a quality 12 inch woofer costing around $1000 and weighing about 25 lbs or more.

I would add that outside of pro applications these kind of woofers are few and far between - buyers will pay for veneer or cabinet work but not for honking great big magnet and voice coil that they cannot even see - of course manufacturers respond accordingly to the customer demand (customer is king).

Without a good expensive woofer the best damping factor in the world is not going to put lipstick on the proverbial pig...
audiokinesis
2,737 posts
 
My understanding is that a woofer's electrical damping is described by the electrical Q (Qes) and the mechanical damping is described by the mechanical Q (Qms). The Qes value given in a spec sheet assumes a true voltage source amplifier, and in practice is raised by the amplifier's output impedance. I think the equation is Qes' = Qes x (Re+Rampout)/Re, where Re = the voice coil's DC resistance and Rampout = the amplifier's output impedance.

Much as I like prosound woofers, most of them have too much electrical damping (too low Qes) to give good bass extension with a low output impedance (high damping factor) amplifier. In other words, most prosound woofers are overdamped for home audio usage when used with solid state amps.

Duke
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shadorne
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[/quote] In other words, most prosound woofers are overdamped for home audio usage when used with solid state amps. [/quote]

Good point - prosound woofers are often in a vice-like grip of the amplifier and excursions are tightly controlled and the bass is often tight and thin compared to the warmer and more extended sound of consumer designs. Partly this design approach helps protect the woofer from damaging over excursions.
pubul57
3,712 posts
 
What are the virtues of a DC-Coupled amplifier like the Atma-sphere?
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