I have always been told your loudspeaker does not need as many tube watts as transistor watts. Why? If the loudspeaker manufacturer says it takes 200 watts for power handling how many tube watts does it take?
Magfan, as you've frequently and correctly pointed out, phase shifts (reflecting the degree to which a speaker's impedance is capacitive or inductive at various frequencies) are a key factor in how difficult a load a speaker presents to the amplifier. Negative phase angles in particular (denoting that the load is capacitive), will increase the amount of current the amp will have to supply (i = C(dv/dt) for a capacitor), while simultaneously reducing efficiency (since capacitors (and inductors) cannot dissipate (consume) any power, apart from whatever amount of resistance may be present).
In the case of George's C1's, though, I suspect it is not too major a factor. As you can see in the Stereophile plots, the phase angle peaks and dips generally occur at points where the impedance magnitude is not particularly low, and the low points on the impedance magnitude curve generally coincide with benign phase angles.
Audioquest4life, thanks for supplying the literature on the Octave amps. I cannot understand the review in "Stereo" magazine, because it is in German, but I did read through the manuals, which I found to be well-written and confidence inspiring. They did not provide information on output impedance or damping factor, though, which is key to my previous post. One clue, though, is the statement on page 35 of the V70SE manual that "the oft-quoted damping factor is not normally a guarantee that an amplifier will exert tight control over the loudspeakers." That would seem to imply that the amp's damping factor is not particularly high, and therefore that its output impedance is not particularly low, which adds a bit of credibility to my previous post.
As far as the "black boxes" are concerned, as you realize their function is to increase the energy storage capacity of the power supply, and also to provide some additional noise filtering. That would seem to be something that can only help and can't hurt (aside from the additional cost), but without either running some careful with/without listening test comparisons, or having an intimate knowledge of the design, I don't think it's possible to say how much of a difference they would make.
Thank you for your technical reponses. You inquired about the Octave amplifiers and you were looking for more information about these amps. I would like to hear your technical response about the methodology employed by Octave for their amplification. I am also a Octave amplifier owner, MRE 130's, and as was stated by another new owner, the bass is incredible. My mono amps sound more powerful compared to SS amps rated higher in wattage. I drive a pair of B&W Nautilus 800's with essentially no problems, and bass loss is only at the very lowest bottom end of the spectrum when compared to a powerful SS amp, but for the majority of music, sometimes I feel as if the bass is comparable to SS Amps with a sub in the system.
These links provide you the information you were asking for regarding the output and THD ratings of both the Octave V70SE and MRE 130's amps. I am wondering on what you think about the use of the Super Black Box to allow more current overhead for the AC delivery.
In one of the German tests, they were using a pair of Nautilus 801's that they claimed never sounded as good until the hooked up the MRE 130's. That is why I have been standing up for the N800's with tubes, the Octave MRE 130's drive these speakers easily and the with the addition of the Super Black Box, adds more capacitance to the power delivery allowing speaker loads down to 2 ohms to be driven easily.
For the masses, I think the explanations on how such a methodology or topology employed succesfully to drive low impedance speakers based on tube technology compares to SS designs.
What role does phase angle play in your analysis, Al? I would ordinarily associate the 'wild impedance swings' mentioned with large phase shifts, as well. Tube stuff, I'm told, doesn't like certain reactive loads.....Capacitive? Inductive?
An excellent (although unnecessarily lengthy) thread on tube watts vs. solid state watts, from last March, can be found here. Several of our most knowledgeable members contributed some good insights, some of which (mainly on a theoretical level) have not yet been stated in this thread.
09-23-10: Xti16 I just traded my Bryston B100 rated at 100w 8ohm and 180w 4ohm for an Octave V70se rated at 70w 4ohms (can't find an 8ohm rating). Anyhow the Octave just crushes the Bryston in power and control. Not bashing Bryston for I had mine for 4 years and thought it couldn't be beat without spending a truck load of money. The demo in my home took about a whole 5 seconds to want the Octave (and that was with cold tubes). I think the caveat here is my speakers. They are Dynaudio C1's which are known to like current not necessarily watts. Rated at 85db 4ohms. Logically it makes no sense unless the power is calculated as E X I instead of I sq X R and Octave uses a lower voltage (E).
I hope Almarg chimes in on this one for he always has good technical answer.
So I'm guessing it has more to do with the speakers where tube watts may seem like more compared to solid state. I don't think that applies to all speakers, but some.
Thanks for the kind words, George.
In referring to "power and control" I assume you are referring particularly to the bass region. I can't offer a definitive explanation for the differences you found between the two amps, but my guess is that the differences are unrelated to tube watts vs. solid state watts, and are unrelated to the maximum power or voltage or current capabilities of the two amps.
What I suspect is that the major reason for your findings is the interaction of the differing output impedances of the two amps with the impedance vs. frequency characteristics of the speakers. As you'll see in Stereophile's measurements, the C1 has some wild up and down impedance swings in the bass region (which are not uncommon, btw), with a sharp rise to 18 ohms at about 60Hz.
I assume that your Bryston amp, like most solid state amps, had a negligibly small output impedance. I couldn't find specs on the Octave amp's output impedance (or damping factor, which equals output impedance divided into 8 ohms). However given that it is a tube amp, and one which, unusually, has only a single output tap on its output transformer, it is probably safe to assume that its output impedance is significant, perhaps 2 or 3 ohms or so.
Since an amp with near zero output impedance acts essentially as a voltage source (within the limits of its current capability), a load impedance rise will not affect the voltage across the load, but will result in decreased current draw, and therefore decreased power into the speaker at the frequency corresponding to that impedance rise.
In the case of an amp having a highish output impedance, the current decrease caused by a load impedance peak will be offset, at least partially, by an increase in the voltage across the load, since (oversimplifying slightly) the voltage the amp is trying to output will divide up between the load impedance and the amp's output impedance in proportion to the two impedances.
So I suspect that the low frequency impedance characteristics of the speaker, particularly the sharp peak at 60Hz, result in the speaker being synergistic with the output impedance of the Octave amp. And of course intrinsic differences in the sonic characters of the two amps could obviously be factors as well.
You know Audiofeil I do appreciate you monitoring this site to make sure nothing bad happens but could you focus a little more attention on the hobby in get off my back.
If you would do that I will close my casket....... No viewing allowed. My kids have been instructed to take the tubes out of my deHavilland Mercury and my GM-70's and place them in my pants.... hopefully that will help me not just to look my best but stay warm in the here after. (dealer disclaimer)
Stanwal, aside from snide disrespectful remarks, did you bother to look at the graph at the Stereophile site that I told you about? I'm sorry that you have to take that tone, it suggests you have other problems. Now do go to that graph, then come back and tell us what precisely you see in that graph that motivates you to show so much contempt.
Tvad, I'm sure you know everything I posted here (ever). You *probably* meant "maximum" instead of "minimum", but that wasn't what I was getting at. It's not just that we humans like one kind of distortion better than another. Whereas for tube amps, the line into "too much distortion" is somewhat arbitrary (1% THD? Why not 5%? 0.1%?), for SS amps, it's much more straightforward: they are either pretty linear, or catastrophic.
When I listen to Mahler's 3rd with the tube amp, I occasionally sigh or smile when the little guy runs out of gas, since it's not so bad and what are you going to do. When I turn on the 275 watt SS beast, I get the symphony in its proper loudness... with a finger right on the remote ready to stop the thing. Living dangerously.
Re-reading the OP again, maybe he was just asking if his speakers would blow up? Man, don't worry, if you can afford a 200 watt tube amp, you can afford new speakers. :)
I was over to my tech friends house this morning, he has over 30 years experience and has had published articles in DIY mags on the design of TUBE equipment. I told him about your statement that a 200 watt amp would give 10% distortion at 210 watts. After a loud burst of laughter he said "he sounds like a real expert". I can't add anything to that.
Stanwal, I went to the Stereophile website and randomly selected a solid-state amp reviewed there (since they have nice graphs in their review). Ok, not so randomly selected--it was at the top of the list and it's probably the most recently reviewed. :)
It's an Electrocompaniet AW400. Looks like a reasonably nice amp, $12,500 (pair of monoblocks). Look at the graph on Atkinson's measurement of power output, Figure 3. The curves do exactly what I said: slow decrease in THD with rising power, until suddenly they hit a barrier and spike drastically upwards.
You might say that SS amps have a dramatic change in the second derivative of their power vs. THD graphs right around their rated output, compared to tube amps. That very different approach to distortion results in the effects that we've been talking about.
So tube amps and SS amps are different beasts when it comes to power ratings, and it is quite valid to make a correction accordingly. A rule of thumb I've seen here and there is that N watts of tube amp is about the same as 3N watts of SS amp, because of this effect.
Now if you can make absolutely, positively certain that your SS amp will never distort as the signal level routinely approaches that boundary, then you can change that rule of thumb accordingly--but that's a toughie.
That is the first time in 7 years that anyone on Audiogon has agreed with me. Having said that I would like to die knowing that on just one occasion Tvad agreed with me. That would make me happy. My casket will be open for viewing.
Sounds_real_audio, I agree with you. I think its more an issue of perceived power than what the speaker will handle. With tubes we tend to be satisfied with fewer watts instead of continuously increasing the volume to bring out something in the music we feel we are missing. Sure, you can get this in solid state electronics, but the price is much higher.
One thing that tube amplifiers/preamplifiers do so well that solid state amplifiers do not is reproduce those wonderful micro dynamics. Those subtle nuances. So when listening to tubes you are not looking so much at the big dynamics like drum beats etc but rather to the subtle musical characteristics and so you don't feel the need to turn up the volume as much, you hear more at lesser volume.
So perhaps not so much about power as about perception.
That is not correct, it depends on the amplifier. My Musical Fidelity NuVista M3 is rated 275 at 8 ohms, my tech friend measured 325 with extremely low distortion. It will pulse over 800 watts at 2 ohms. Any good amp will deliver much more than its rated power for very short bursts, that was the basis of the late , unlamented "peak" power or "music" power ratings. Any amp that behaves as you describe is a bad amp and should be avoided.
There's lots of informative answers here but I'm not sure they have answered the original question.
When an SS amp approaches its power rating, it will go into distortion very, very quickly. Suppose it is rated at 200 watts; then if you try to get 210 watts out of it, you could easily get 10% THD or more. It will sound totally horrible. So in practice, you would not actually want to go anywhere near 200 watts with such an amp, because the power level of a music signal varies greatly and you are just asking for trouble.
On the other hand, the tube amp rated at those same 200 watts (this would be a little beast btw) can go to 210 watts and the THD might not go a whole lot higher than 1%.
So it's not so much that the tube amp is more powerful than its rating, but rather that the SS amp is not as powerful as its rating (by comparison); that's how I think of it.
That, and the realization that 30 watts is a whole lot louder than we think. :)
Even a solid state amp that claims 200 watts of power does not make it a certainty that if impedance drops below 4 ohms and closer to 3 will it do the job without current. High, stable current with lots of reserve at the ready. Without it watts mean little in either camp. IMHO. Cheers
Musicnoise If I half the voltage that would double the current to get the same watts. If a speaker works better with higher current then it would be beneficial. Not all speaker will benefit from high current though. That's what I am trying to say.
TVAD, it is :-). My speakers are spec-ed at: 4 Ohms nominal, 4 Ohms minimum. Many, if not most tube amps have 4 Ohm taps. In such a case, if one was willing to provide double the 8 Ohm tube Watts as a similarly rated 8 Ohm "double down" ss amp, all should be equal. If the speaker impedance load was 16 Ohms, the opposite would be true. Of course, I'm sure you knew that, but, it does clarify things for the OP.
xti16 - as to your reference to power calculations, it makes no difference which form of the equation you use, they are synonomous. To state otherwise ignores ohms law.
Just because a speaker says "200 watts power handling" doesn't mean that it requires 200 watts to function. The 200 is a maximum, not a minimum and only a very loose maximum at that. Ratings in watts tell you very little about how any amp, tube or transistor , will drive any particular speaker load. Many lesser rated amps of either type will drive speakers that amps of higher rating have trouble with. The output transformer of tube amps smooths out difficult loads in many cases. Conversely the early Classe SS amps were rated at about 25 watts but would drive one ohm loads that would blow up many amps of 200 watts or more. The moral, all watts are not created equal, tube or transistor.
This is good question. Until 2 weeks ago I would have said the same as Tvad and Grinnell. But it may be more than that. I just traded my Bryston B100 rated at 100w 8ohm and 180w 4ohm for an Octave V70se rated at 70w 4ohms (can't find an 8ohm rating). Anyhow the Octave just crushes the Bryston in power and control. Not bashing Bryston for I had mine for 4 years and thought it couldn't be beat without spending a truck load of money. The demo in my home took about a whole 5 seconds to want the Octave (and that was with cold tubes). I think the caveat here is my speakers. They are Dynaudio C1's which are known to like current not necessarily watts. Rated at 85db 4ohms. Logically it makes no sense unless the power is calculated as E X I instead of I sq X R and Octave uses a lower voltage (E).
I hope Almarg chimes in on this one for he always has good technical answer.
So I'm guessing it has more to do with the speakers where tube watts may seem like more compared to solid state. I don't think that applies to all speakers, but some.
I agree with Tvad, except some manufactures recommend power needs assuming that the 8 Ohm rated power of the amplifier will "double down" into the lower impedance that their speakers actually work in. That might require more (8 Ohm) tube Watts than ss Watts.
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