[thesteve]

I definitely wants to spin this off of the "Metal Amp" thread in the Amps forum

Here's the pertinent posts so far:

Originally Posted by RubberChipmunk

Wattage does not equal volume. The two aren't even related at all, although the amp's max wattage will have a tiny bit to do with the maximum volume you can get. Wattage is actually a measure of electrical power. Your everyday 100w amp isn't even outputting 100 watts unless you dime the thing, and even then, its probably more an estimate than an exact value. To put in perspective just how little wattage has to do with volume, a 10w tube amp is only half as loud as a 100w amp. So a 5w amp is going to be about half as loud as a 50w amp. The HT-5 is plenty loud enough to be used for any application you could throw at it.

Originally Posted by What5647

Actually, that is not entirely true. For a SS or digital amp, the above statement is correct. However, tube amps are different. Wattage = clean headroom/energy output. When you exceed that headroom, you're putting out more watts, but the sound is now distorted. I forget the exact number, but a dimed 100W tube amp in heavy power amp distortion is putting out far more than 100 watts. This is very important if you're playing with different speaker cabinets with difference wattage ratings.

Granted, a 100W amp dimed like that will be mind-bogglingly loud, (been there, done that, not doing it again...well, maybe...) but the principle applies for any tube amp.

Oh, one more thing: Wattage and volume aren't directly related, but they are related. Thing is 100W isn't that much louder than 50, and 5 is still more than loud enough.

Originally Posted by RubberChipmunk

No, that is quite true. Wattage is a measure of electrical power, nothing else. This means that a 100w amp is capable of pushing 100 watts of power through speakers. The more wattage = more volume myth is definitely not true, even though it does have an effect. Although 100 watts can be twice as loud as 10 watts, 10w through 4x12 will be louder than 100w through 1x12. Now, while higher wattage tends to mean more clean headroom, once you hit the saturation point for the power tubes, that doesn't mean you're at 100w. You can't make it louder and suddenly its 120w. That's not how it works.

Its recommended that you get speakers that add up to more than your amp's highest wattage for two reasons. The first is because electronics is NOT an exact science. You can get close, but you cannot get exact. Your iPod is slightly different than your neighbor's iPod because components can have error ratios of up to +/- 10% for standard components or as low as +/- 1% for precision components (which are pretty expensive). This means that a 200K ohm resistor could in actuality be anywhere from 180K to 220K ohms of resistance, regardless of what it actually says. Same thing with capacitors, and many other components. In the poweramp, this can affect the output wattage very slightly. Even the tubes can affect the wattage, because they are by nature imperfect. So your amplifier wattage rating, whether solid state or tube, is an approximation anyway. Then there's the other reason, which is that electrical power needs to go somewhere. Generally, it gets converted into something. One common thing to convert power into is heat. This is why lightbulbs work. This is why you see giant heat sinks on things. The component they are protecting cannot handle the power being sent into it, so the heat sink helps keep it cool. For speakers, they convert electrical power to sound waves. But try running something at its maximum specs for a long period of time and you start drastically reducing its life span. This is why we bias tubes to an optimum level below their maximum specs. If you were to run exactly 100w into a speaker that will convert up to 100w of electrical power into sound energy for a long period of time, even considering perfectly precise components, you're going to shorten its lifespan. If you dime it, and the component variance puts your 100w amp OVER 100w, and your speakers can only handle 100w, then you are damaging your speakers.

So, I stand by everything I said.

Originally Posted by thesteve

Eric,

Can you provide sources for this? My understanding is similar to his, that tube amps are rated for wattage output within the spectrum of their clean headroom and that tube amps can be pushed beyond these clean levels as it clips the signal.

Originally Posted by What5647

<--- EE student, and electronics technician by profession. So, no need to lecture me on the fundamentals of electronics.

Wattage is the work being done, and the work here is converting an electrical signal to an audible signal. Granted, there are things that impact this, but under the same conditions, a 100W amp will have more clean volume than the 10W. It's kinda pointless to say that a system using more energy is not going to be louder. (Barring gross inefficiency.) That's like saying a 100 HP car will be faster than a 1000 HP car. Sure, it is possible that there is enough drivetrain loss that you lose over 900 HP between the motor and the wheels, but that just doesn't really happen.

Now, if the 100W amp is SS and can at max, dimed setting output 100W, while the 10W amp is tube and can output 110W before total tube saturation, (yes, that's a very unlikely figure) it will be louder than the 100W, assuming the same speakers are used.

Also, my understanding is that most 100W modern tube amps will output around 150W when dimed.

And still, a 10W amp will be more than loud enough.

Originally Posted by BillSPrestonEsq

Thats what I have heard and read as well.

Originally Posted by RubberChipmunk

I haven't heard or read that understanding of wattage before. I'd be glad to discuss this in another thread if someone would like to start it. I don't want to hijack this one.

I wanted to continue the discussion in saying that the "tubes go above their spec'd wattage" is one common argument that is made in the discussion of why tube amps seem to be louder than similarly spec'd SS amps. That is to say (as What5647 noted above), an SS amp will hit it's clean threshold and basically be at maximum watts. It will clip quickly beyond this point. On the other hand, a tube amp will clip more gradually and as such will have more functional wattage beyond it's clean headroom rating. I believe this logic is roughly based on the idea that amp power ratings are often made at a given impedance and % total harmonic distortion (THD) and that if the measurement were taken at a different %THD, then the wattage rating of the amp would change accordingly.

In the case of SS vs. Tube, this would effectively mean that both amps might be rated at 100W at 5% THD. The SS amp (hypothetical) would reach 100% THD faster (and according to the "SS amps don't break up well" crowd, in a less pleasurable manner) than a tube amp would. As such, a SS amp might incur harsh, unusable clipping when the circuit is pushed to 105W, whereas the tube amp circuit may handle upwards of 130W+ simply because it is clipping the signal in a manner that is more pleasing to the ear.

[RubberChipmunk]

Oh wow, this ended up in Electronics. This is EXACTLY what this forum is for. This makes me very happy.



Like I mentioned, I have never heard that understanding of wattage in relation to guitar amps and clean headroom before. I also have an electronics background. I spend my days designing circuits for, among other things, guitar amplifiers, and I spend a lot of time studying electronics theory, tube theory, etc. So, I'm no slouch when it comes to things like this. I'm no expert, but I'm not a complete newbie. I have been informally studying electronics for at least five to six years, moreso recently, and I learned the basics in high school.

My current view is this:
Lets take, for example, a Quad of JJ 6L6GCs. According to JJ's data sheets, their 6L6GC has an upper limit of 30W, reachable under the maximum operating specs. Running a single 6L6GC over 30W will damage the tube. This means a maximum power handling of 120W. Typical operation for the 6L6GC shows about 17.5W per tube, or 70W for the quad, in Class A Push-Pull under those typical characteristics. One of those characteristics is, I believe, the signal applied to the grid. Using the power derivative of Ohm's Law, you can assume that the 17.5 W per tube will not be static and will fluctuate depending on the amplitude of the signal at any given time, among other factors.

Because of electronics not being an exact science, it would make sense to me for that 70W amp to be outputting anywhere from 65-75W at maximum volume. An amplifier's stated wattage, to my understanding, is based on what you can expect at maximum volume given the operating conditions of the output stage, whether it be vacuum tube, transistor, or OPAMP.

If this understanding is not correct, why?

[thesteve]

I think the differences in our understanding isn't coming from the theoretical side, but coming from the measurement. When I see a rating of "100W @ 4ohms w/ 5% THD" what that says to me is that the wattage could theoretically increase given a higher threshold THD (say 10% vs. 5%). I've even read stories of manufacturers using higher THD tolerances in order to make their amps seem bigger than they really are.

I agree that running a tube above the theoretical limit (say 30W) will damage the tube. I don't think anyone will try to argue that running an amp into tube saturation territory is bad for the tube, only that it's possible to push a tube beyond the specs given by the manufacturer and that when this is done the tube will saturate (increase in THD) and as such the total wattage (output) will be higher than the spec'd point.

[RubberChipmunk]

Originally Posted by thesteve

I think the differences in our understanding isn't coming from the theoretical side, but coming from the measurement. When I see a rating of "100W @ 4ohms w/ 5% THD" what that says to me is that the wattage could theoretically increase given a higher threshold THD (say 10% vs. 5%). I've even read stories of manufacturers using higher THD tolerances in order to make their amps seem bigger than they really are.

Can you clarify this any? It seems like you're saying that its not an issue of theory, but you still mention that wattage could theoretically increase given a higher THD, which to me sounds like theory. I'd like to understand how this actually works, because I've never heard anything about this before.

I agree that running a tube above the theoretical limit (say 30W) will damage the tube. I don't think anyone will try to argue that running an amp into tube saturation territory is bad for the tube, only that it's possible to push a tube beyond the specs given by the manufacturer and that when this is done the tube will saturate (increase in THD) and as such the total wattage (output) will be higher than the spec'd point.

But those specs given by the manufacturer are given as limits. We can push tubes beyond the specs given for "typical operation," but even then, we don't even set them close to maximum limits because that would kill the tube.

[thesteve]

Originally Posted by RubberChipmunk

Can you clarify this any? It seems like you're saying that its not an issue of theory, but you still mention that wattage could theoretically increase given a higher THD, which to me sounds like theory. I'd like to understand how this actually works, because I've never heard anything about this before.

"Theoretically increase" was a poor choice of words. My point overall was that when an amp manufacturer says their amp is a 30W amp what they often mean is that their amp puts out 30W output given 4 ohms at a limit of 5% THD (or some other level THD). My understanding is that this value represent "clean headroom" and that the amp will go beyond that %THD with increased wattage. The amp manufacturer simply did not measure the wattage at those increased THD levels.

But those specs given by the manufacturer are given as limits. We can push tubes beyond the specs given for "typical operation," but even then, we don't even set them close to maximum limits because that would kill the tube.

Right, but my understanding has always been that the given limit is still playing it safe. As such, the 30W rating given to a 6L6GC tube is the recommended limit, but the tube itself will go beyond that point without instantly dying.

[RubberChipmunk]

Originally Posted by thesteve

"Theoretically increase" was a poor choice of words. My point overall was that when an amp manufacturer says their amp is a 30W amp what they often mean is that their amp puts out 30W output given 4 ohms at a limit of 5% THD (or some other level THD). My understanding is that this value represent "clean headroom" and that the amp will go beyond that %THD with increased wattage. The amp manufacturer simply did not measure the wattage at those increased THD levels.

I see. I have never once heard that before. Interesting. I've been under the impression that a 30W amp is not putting out 30W unless you're turning the volume up. I don't see how simply having a higher %THD can push a tube beyond its theoretical limits, to be completely honest. The audio signal is just clipping because its higher than the tube is capable of reproducing cleanly, an effect of the fact that you have free electrons flying through a vacuum as a result of being kicked off a metal electrode by a lot of heat. Whatever values the Cathode, Plate, Screen Grid, and Suppressor Grid (in Pentodes) have been set to remain more of less static. The negative bias voltage to the Grid can be changed (in Class AB1 operation), but more or less once set it stays completely the same. The only thing that could change rapidly is the amplitude of the audio signal, and I just don't see how a relatively weak audio signal applied to Grid could push a tube beyond its limits or truly affect anything significantly just because its "louder," unless we were already set at or above these limits for the rest of the electrodes. I can understand 0-30 based on how the 30w amp is setup, but is it really going to go that much above 30 because of an audio signal?

I suppose the best way to really find out is to take a few amps, open them up, and test them. I might have time to do that with my Blackstar this weekend, once i can figure out a good, safe way to do it.

Right, but my understanding has always been that the given limit is still playing it safe. As such, the 30W rating given to a 6L6GC tube is the recommended limit, but the tube itself will go beyond that point without instantly dying.

But we don't even set the tubes close to the given limit. I cannot think of one amplifier that even comes close to that limit. For this to make sense to me, I need to believe that the "volume" of the audio signal can really be strong enough to push a tube above its limits when everything else about it has been set below its limits.

[RubberChipmunk]

Some information that I just found points to wattage on tube data sheets being strictly plate dissipation, and the audio output being seperate and also measured in watts. I could be mistaken, but that would lend a lot of water to what you are saying being true. Its difficult for me to be certain, as I've spent a very long time (couple of years I think, its not just a recent thing because I'm finally getting around to starting the amp company...) researching this stuff to build amps, and this is the very first I've heard of this. I have to work some theory out. Anyone have any math on this already done?

[thesteve]

Originally Posted by RubberChipmunk

Some information that I just found points to wattage on tube data sheets being strictly plate dissipation, and the audio output being seperate and also measured in watts. I could be mistaken, but that would lend a lot of water to what you are saying being true.

Hmm...I suspect when amps (at least audio) are measured as "X watts" it's the latter, but I didn't even this about there being a difference here. Interesting...

[RubberChipmunk]

Originally Posted by thesteve

Hmm...I suspect when amps (at least audio) are measured as "X watts" it's the latter, but I didn't even this about there being a difference here. Interesting...

They are apparently typically measured as "X Watts RMS." With this distinction in place, everything both of us have said in this thread theory-wise is correct, except for what we were applying that theory to. It can also be measured in Peak Power to give a higher advertised output wattage, or in Peak Music Power Output, which is generally what 1000+W car audio systems are measured in. This now makes a lot of sense.

Here is the page I have been referencing for this: GM Arts - Guitar Amplifiers.

[thesteve]

Originally Posted by RubberChipmunk

They are apparently typically measured as "X Watts RMS." With this distinction in place, everything both of us have said in this thread theory-wise is correct, except for what we were applying that theory to. It can also be measured in Peak Power to give a higher advertised output wattage, or in Peak Music Power Output, which is generally what 1000+W car audio systems are measured in. This now makes a lot of sense.

Here is the page I have been referencing for this: GM Arts - Guitar Amplifiers.

That makes sense, I hadn't brought in my understanding of "RMS" because I wasn't entirely confident in how it was applied in guitar amplification. I know some power amp companies have advertised Peak Output while their competitors advertise RMS output in order to gain an "edge" in the watts department. Often when you take a good look at the literature, the latter company has both a higher RMS and Peak than the company that only advertises Peak.

[RubberChipmunk]

Originally Posted by thesteve

That makes sense, I hadn't brought in my understanding of "RMS" because I wasn't entirely confident in how it was applied in guitar amplification. I know some power amp companies have advertised Peak Output while their competitors advertise RMS output in order to gain an "edge" in the watts department. Often when you take a good look at the literature, the latter company has both a higher RMS and Peak than the company that only advertises Peak.

Well, now we know, and knowing is half the battle.


On a semi-related note, In the process or researching for this thread, I have learned some soft and hard clipping distortion circuits and I might be building a pedal soon. I freaking love electronics.

[RubberChipmunk]

Just noticed this.

If you take a look at the tube sheet I posted earlier for the JJ 6L6GC, you'll notice that under Typical Characteristic: Class A1, the variable N is used to show watts, but under Limiting values, Wa also shows a wattage rating. Wa is the maximum plate dissipation (wattage on the anode, or plate) which cannot be exceeded, which would lead me to assume that N is output watts. This would seem to show that N could fluctuate quite a bit.

This would also mean that, if RMS output WERE generally tested at 5% THD, then more distortion could have an effect on the output RMS power, though I'm still not completely convinced its going to swing enough to actually need to use a speaker load with more power handling. Aren't instrument speakers are designed to handle this? Isn't a 30W instrument speaker able to handle 30W linearly, 45W (150%) non-linearly, and above that will damage the speaker or destroy the coil? I'm going to need to see more data on tube operation under varying levels of THD, and I still need to see something that shows that RMS is, in fact, generally calculated at a certain percent THD.

[thesteve]

I've always been under the impression that a speaker's wattage rating is a conservative value and that a speaker spec'd at 30W will handle more than 30W under at least temporary conditions.

I'm not sure if there's any technical data sheets on it, but I have the user manuals for both the Fender Hot Rod Deluxe and Blues Deluxe, and both of those amps are rated at 40W into 8 or 4 ohm at 5% THD. No indication if that rating is peak or RMS, though I have always just assumed it was RMS.

I did just find the manual for the Crate V33 212 online. That amp is rated at 28W RMS @ 10% THD, 8 ohm load.