Power/Volume difference Tube vs Solid State

[888guitars]

I had a hard time explaining to a customer why a tube sounds louder than a solid state amp of the same power? Anyone have a good way of saying it in simple terms? If you talk ohms law (on paper) they should be the same.

[loudthud]

When amps are tested for power output, a resistive "dummy load" is connected in place of the speaker. Amps react differently when a speaker is connected. A tube amp can deliver more voltage to a speaker than it can a dummy load but a solid state amp delivers nearly the same voltage to a speaker or dummy load.

[teemuk]

First, output power is not the same thing as perceived loudness / volume. It only tells how much power the amp can feed to a certain load with certain % of THD. There's tons of other parameters besides output power rating that must be known as well before any judgments about amp's loudness can be passed.

Second, tube amps being louder than solid-state amps is a generalisation and doesn't hold truth in all cases. People spreading that claim likely just haven't experienced loud solid-state amps like e.g. JC-120, Legends, Sunn Beta Lead or Peavey Special 130.

Some amps are louder than some other amps, even if they happen to have the same output power rating. That applies to SS vs. tubes as well as to SS vs. SS and tubes Vs. tubes.

[Wilder Amplification]

The way the amp is voiced plays a big part in it as the human ear does not hear "flat" (i.e. it is more sensitive to some frequencies more than others) and the response of our hearing changes with volume (Fletcher/Munson curve). Be it tube or solid state, if we had two amps of identical clean power ratings but amp A is voiced in favor of the frequencies that are ears are more sensitive to vs amp B whose voicing is very "flat", amp A will be perceived by the human ear as being louder than amp B even though they are of an identical output power rating.

Another thing to consider...and this is just a theory of mine so take it for what it is...but solid state amps produce harsh sounding harmonics when they clip compared to that of a tube amp. We naturally like the sound of a tube amp when it distorts over that of a solid state. As we know, an amplifier be it tube or SS produces more power than its rated clean power when it clips. However, when a tube amp clips we tend to like that sound which creates the subconcious tendency to either wanna leave it at that volume setting or crank it even further, which puts us in the "clipped/distorted power" region and is greater than that of its max rated "clean" power.

But SS amps don't sound very good when they're driven into clipping which makes us want to turn them down to the point where they're not clipping, which limits us to the max rated clean power or less.

Of course, load impedance varies with frequency so power output is never constant in either scenario.

[Enzo]

When you try to explain it, please keep in mind the difference between comparing a 50 watt tuibe amp and a 50 watt SS amp, and then comparing 50 watts FROM a tube amp and 50 watts FROM a SS amp. Though it gets distorted in the retelling, the claim has never been that watts are louder coming from a tube amp, the claim is that a 50 watt tube amp will generally sound louder than a similarly RATED SS amp.

As you turn up a SS amp, you run into clipping, which is a brick wall and sounds like crap. As you turn up a tube amp, the signal rounds off the tops and compresses rather than simply clipping. There is no brick wall clipping in tube amps.

As with any rule of thumb, I am sure someone can come up with examples to the contrary, but overall, most of the time, same-powered and same-speakered amps will find the tube one able to make louder sounds.

[R.G.]

Good reply Enzo.

Russell O. Hamm's paper on tube preamps explains some of it. His comment is that a tube gain stage distorts in a way that makes the first 12db of clipping sound like it's increasing in volume when it's actually being compressed and slightly distorted.

[teemuk]

As you turn up a SS amp, you run into clipping, which is a brick wall and sounds like crap. As you turn up a tube amp, the signal rounds off the tops and compresses rather than simply clipping. There is no brick wall clipping in tube amps.

Yes there is, and you as a tech should know it out of all. Even a quick session with oscilloscope examining the output of a tube amp will show that they will produce flat-topped waves with rather sharp knee when overdriven to clipping. An odrinary solid-state tube scremer effect clips just about as softly, another thing that an oscilloscope can quickly reveal.

YouTube - ‪tube cube guitar amp demo scope view‬‎

http://www.youtube.com/watch?v=aA9-t3C9m7o

Furthermore, even if there's a slight curvature in the knee from linear operating area to total saturation it's effect is maybe one or two decibels of increased headroom. That doesn't explain the typical claims of 2 - 3 x louder tube amps. Those kinds of differences would require that the tube amp could magically produce about 10 x more power than a solid-state amp.

[Wilder Amplification]

Despite all of the claims here, I'm here to invent electrical theory AND I have "golden ears" so only my posts hold water. I'll even install 1 ohm 100% resistors with every impedance speaker load on every tap just for the sake of supporting my claim.

[J M Fahey]

The answer is complex, mainly because usually apples are compared to oranges.
1) The typical boilerplate assumption that "tubes sound 2-3 times louder than SS", when investigated further compares a 15W SS amp, "beginner type" with a skimpy 8" speaker, with a dime sized magnet and around 92 dB efficiency to a VOX AC15 or a Matchless driving two Vox Blues or a V30+Greenback cabinet with 100 to 102 dB efficiency. Very unfair !!
When plugged into the same speaker things start to even out, although, admittedly, Tube still holds an advantage.
2) The difference is most apparent in the "transition" area, say 5-6 on a Twin to speak of a Classic amp.
The tube one will not *sound* distorted, although a scope will show that it is starting to do so, but output pentodes will start compressing, plus distorting in a "non harsh" way, which combines into perceived liquid sustain, fatness yet clearness, etc. , all good. Many musicians will try to stay there, even calling that the "sweet spot"
Also harder or lighter picking become useful means of sound control.
An SS amp, at the same amount of clipping, will offer no compression, harsher clipping, and when changing pick pressure will get either harsh or "boring clean".
Most musicians will hate that and lower volume to avoid that area, so the amp, yes, in actual use will be providing less volume than it's capable of.
3) If you use the amp *always* clean, a properly designed SS amp *with an excellent compressor/limiter* and good speakers will provide tons of clean volume.
Just listen to that Peavey specialty, those excellent Pedal or Steel Guitar amplifiers they make.
Also, if music does not require approaching the full power output, as in Jazz amps, SS holds its own very well, as shown by those Polytones, JC120 and such.
3) If you always use your amp *very* distorted, favoring buzzsaw sounds, the difference also blurs, and SS amps can also hold their own very well, as in those Randalls or Ampeg/Crate VH140.
***All this driving the same kind of cabs***
4) Because of very different distortion mechanisms, tube amps start sounding real good from 6-7 up, with "10" providing even a perceived higher volume.
On SS amps, usually the maximum perceived volume is 6-7 , and 10 not only not providing an audible increase but even getting lost in the mix, although measurement instruments show an increased (squarewave) power.
My pet theory (which of course can be wrong) is that when clipping tubes still retain a lot of the note harmonics, which give it character and can be recognized ; while SS brutally clips tops and kills most harmonics, providing loud but dull sound.
But the traditional explanation that "SS provides squarewaves, tubes do not" and "SS provides odd harmonics, Tubes even ones" does not resist the easitest test: hooking a scope to the speaker terminals.
The much quoted Russell Hamms paper refers to Mic Preamps, very interesting and useful but unrelated to what power amps do.
2 final notes:
1) diodes (as in a Tube Screamer) distort much rounder than any tube (please hook a scope there) , but do not compress at all.
2) SS amps, when brilliantly engineered, can become "Tube killers" .
Best example: impressive L5, which certainly did everything well: 200W power section, good compression, even harmonic generator and LOUD EV speakers.
It could sure beat a Twin in any side by side comparison, playing live on a BIG stage.
I know I will be stoned by this last comment, but believe me, I've tested them side by side on Stadiums and the difference was impressive, in favor of the L5.
I think it "died" by commercial reasons (limited availability, too expensive), certainly not because of its sound, and also because Twin type amps, in general, became much less desirable than Marshall type ones, at least from a massive market viewpoint.
Just my 8 Peso cents (which amount to about 2 US$ cents )

[888guitars]

I do agree with the "percieved" difference when looking at the fletcher/munson curve. I think the best "simple" answer that I'm getting from you guys is that when you are clipping the output the tube will still continue to put out decent sound, where as the SS will not be good at all. I think that will keep customers happy with the answer. And its true! Not a guitar center answer. Thanks! ...I also was thinking about the difference in construction (log/linear) one amp on 3 might be almost full power and another might actually be on 3.

[d95err]

An SS amp has to be able to provide clean power for the peak of the guitar sound. The tube amp can happily clip and compress much of the peak while sounding good (and more or less clean). Thus, the SS amp delivers much lower volume to the sustaining part of the note than the tube amp. This explains why an SS amp needs to deliver 2-3 times more power to be as loud as a tube amp on clean(ish) sounds.

On heavily distorted sounds, the difference in max loudness should be much smaller.

[888guitars]

That makes good sense. I believe the average human ear can only hear in increments of about 3-4% distortion at 1k per 3db

[Enzo]

If you present a sine wave and then add some distortion, that can be easy enough to detect. But play music through it, and all of a sudden distortion is a lot harder to pick out.

[teemuk]

If you present a sine wave and then add some distortion, that can be easy enough to detect. But play music through it, and all of a sudden distortion is a lot harder to pick out.

Truth. Also, it's a lot easier to detect distortion from entire musical arrangement than from one guitar within that arrangement. Guitar players can tolerate a lot of distortion in the signal because the instrument usually works on a rather narrow band of mid-range frequencies and because distortion is even accustomary within the context. It's less like that with amps for stuff like bass guitars, synthesizers/keyboards, drum machines, PA, etc.

[Steve Conner]

I've been messing around on the "dark side" lately and I tend to agree with the above comments. I don't see any fundamental reason why a transistor or hybrid amp shouldn't sound as loud and as good as an all-tube one.

I'm currently experimenting with a hybrid based on a little 3 watt single-ended tube amp. This can be fed to the speaker directly, or through a 10dB attenuator, or through an "afterburner" transistor output stage that increases the power to about 40 watts. The tube amp also has power scaling by varying the screen voltage of the EL84.

Using the 40 watt setting, with the screen voltage turned right down, I can get some incredibly fat and rich tones that sound nothing like the stereotypical "transistor sound". I wasn't expecting this to happen. Also, with all the knobs turned full up, it makes a hell of a lot of noise.

The Beta 8 is possibly not the best speaker choice, but I wanted to use that cabinet with the 8" speaker hole, I had the speaker kicking around, and I can't think of another 8" that would handle the power. Also, I won't cry too much if I blow a transistor and fry the speaker with DC.

I've tried it through a 12" Alnico Gold, and it sounded considerably better, and considerably louder.

The transistor output stage is my trade secret right now.