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Watts are watts - so what's up?


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Watts and relative loudness... your thoughts?

X% louder = 2^log10(P2/P1) * 100%

40 watts is 94% as loud as 50 watts.

30 watts is 86% as loud as 50 watts.

25 watts is 81% as loud as 50 watts.

22 watts is 78% as loud as 50 watts.

20 watts is 76% as loud as 50 watts.

18 watts is 74% as loud as 50 watts.

15 watts is 70% as loud as 50 watts.

12 watts is 65% as loud as 50 watts.

10 watts is 62% as loud as 50 watts.

9 watts is 60% as loud as 50 watts.

8 watts is 56% as loud as 50 watts.

7 watts is 55% as loud as 50 watts.

6 watts is 53% as loud as 50 watts.

5 watts is 50% as loud as 50 watts.

4 watts is 47% as loud as 50 watts.

3 watts is 43% as loud as 50 watts.

2 watts is 38% as loud as 50 watts.

1 watt is 31% as loud as 50 watts.

3/4 watt is 28% as loud as 50 watts.

1/2 watt is 25% as loud as 50 watts.

1/4 watt is 20% as loud as 50 watts.

1/10 watt is 15% as loud as 50 watts.

50mW is 13% as loud as 50 watts

20mW is 10% as loud as 50 watts.

10mW is 8% as loud as 50 watts.

5mW is 6% as loud as 50 watts.

1mW is 4% as loud as 50 watts.

0.5mW is 3% as loud as 50 watts.

0.1mW is 2% as loud as 50 watts.

50uW is 1.6% as loud as 50 watts.

10uW is 1% as loud as 50 watts.

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I am confused by what PAULN is trying to communicate with that table of values.

Watts are physical measure of power. Loudness is perceptual atrribute that is certainly a function of power. But the relation that is listed is not a good description of the function that relates loudness to power.

I must have missed what you were thinking on this.

-Tom

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Probably the first thing I ever learned about amps was "to double the apparent volume requires 10 times the watts." That is reflected in this table, along with the intermediate relationships all of which are interesting.

I enjoyed reviewing it.

Dave

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On 6/28/2005 11:34:36 AM PrestonTom wrote:

I am confused by what PAULN is trying to communicate with that table of values.

Watts are physical measure of power. Loudness is perceptual atrribute that is certainly a function of power. But the relation that is listed is not a good description of the function that relates loudness to power.

I must have missed what you were thinking on this.

-Tom

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I think PAULN is pointing out that we hear amplitude in a logarithmic not liner manner. He gave the equation for calculating how much "louder" one signal will sound (P2) compared to another (P1), then gave examples using 50 watts for the reference (P1) value.

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Greetings,

I had an interesting conversation with Dusty Vawter of Channel Island Audio this afternoon. I've been going back and forth between my single-ended tube amp and my SI tripath amp and decided to try the SI with a more substantial phono preamp than the one I've been using to see how it would fare overall against the tube amp. So I ordered one from Channel Islands.

After I completed the business end of my order, I inquired about how CIA's monoblock amps (one a version of the "gaincard" chip technology, the other a non-Tripath twist on class-D switching technology) would compare to the SI. Among other things, Dusty mentioned that some folks might be hearing some soft distortion in the SI since the amp develops only about 5wpc.

I find this interesting because everyone I know who's heard the SI has exclaimed, "Man, that sounds like tubes!" (Ok, maybe not an exact quote... 2.gif) On the face of it, such a statement doesn't seem reasonable since tube and switching technologies seem light-years apart. But if part of what folks are hearing is, indeed, some very soft, even-order harmonic distortion from the SI, then the "sounds like tubes" statement makes some sense.

At any rate, just another item for discussion...

Take care,

Scott

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I suspect what people respond to with the switching amps is the overall low distortion at low power. Many (possibly most) ss amps have increasing distortion as power drops below a Watt. switching amps can maintain very low distortion (even and odd harmonics) well below a Watt.

Distortion in tube amps also tends to drop at lower powers. Depending on feedback implementation, or no feedback, distortion may eventually begin to rise at very low power (but the same is eventually true of the switchers at very low power).

Leo

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On 6/29/2005 6:21:32 AM leok wrote:

I suspect what people respond to with the switching amps is the overall low distortion at low power. Many (possibly most) ss amps have increasing distortion as power drops below a Watt. switching amps can maintain very low distortion (even and odd harmonics) well below a Watt.

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Leo,

Are you talking about distortion according to test equipment or distortion according to whether a person notices it with his hearing? What is the threshold of audible distortion? Can anyone tell the difference between .001% distortion and .01%, which is ten times the amount? What about the audibility or lack thereof depending on different source material?

I'd also be interested in your comments to page 5 of this relevant thread:

http://forums.klipsch.com/idealbb/view.asp?mode=viewtopic&topicID=51538

Especially Shawn's comments, which, to my reading, indicate that some people prefer amplifiers with *more* distortion and they are just assuming that the reason they like their choices is because they think their amps have *less* distortion.

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Paul,

In all cases I am refering to amplification at a level in which the amp is not clipping, or even close to clipping. That's just for clarification.

I suspect a person's threshold of distortion depends on the type of distortion.

Crossover distortion is a strong characteristic at low powers in many pp ss amps. A subset of crossover distortion is nonlinearities that result when feedback can no longer compensate for transistor nonlinearities as they turn on/off in the crossover region. This type of distortion is very annoying and is constant amplitude. Because it is constant amplitude it becomes a greater part of the output as power drops.

On the other hand, the output of a tube triode in single ended configuration becomes increasingly linear as power drops. What distortion there is is not as objectionable as that of the ss variety at equal %.

The output of the Tripath technology tends to maintain a constant distortion level as power drops (that distortion being something more like noise). At something like 90dB (this varies / technology) down from full power, there is a noise floor. Again, what distortion there is is not as objectionable as that of the ss variety at equal %.

SS in single ended configuration is somewhere between the triode tube and Tripath.

In order to sound acceptable to someone, at a few Watts, the distortion level of each of these amps would be different. The tube amp, it seems, could have the highest level of distortion and still "sound" good. However, As power drops, the pp ss amp is at a disadvantage because its distortion is easily detected and it tends to rise sharply as a % of the signal.

As a reference, The Tripath chip used in my P6D is specified at .03% distortion from about 6 Watts to about 0.5W. I suspect below that, noise, becomes a greater % of the signal and so the "distortion and noise" figure would rise.

I'm sure my SET never comes close to .03% distortion.

As to my preference? I think the SET is wonderful with low amplitude, not very dynamic selections such as classical chamber, violin & harpsichord, some orchestral selections, esp massed strings. The SET's sensitivity to speaker impedance is a problem that I wish wasn't there, but for now, it's the best I have. I prefer the Tripath (through the Chorus-II) for more dynamic selections: Quintets w/ piano, trios w/ piano, piano. All of my amps have limited power, and I wish they had more, but I don't know how to increase power without loosing the low end I've worked so hard to get right. I am thinking of building a SS class A amp that I hope will have the low end capability of the SET and dynamics of the Tripath and a little more power than both.

I meant to directly address your question, but I find the different technologies are so dis-similar that direct comparison is difficult.

Leo

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On 6/30/2005 12:30:01 PM leok wrote:

I'm sure my SET never comes close to .03% distortion.

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How do you know this?

Thanks for your replies. I have not seen distortion specs for solid state amps at low power output. Do you have a ballpark distortion figure for a "typical" SS amp at 1W, say?

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Tube triode distortion is whatever one wants: just pick a power. So I guess at low enough power the distortion is .03%. Take a look at the last page of the attached KT66 specs I have attached. I doubt the general shape of distortion specs for any tube triode vary much from the KT66 example. The point is distortion drops with power. Notice the shapes of some of the other configs. From the curve it looks like the KT66 config in my pp amp is about 2% distortion at 5W (class A, no feedback, pp). I suspect over 5 Watts or so the amp goes to Class B, and my amp doesn't operate there.. A SET would have a similar curve, just lower power.

Almost all pp SS amp distortion vs power look the same. They are minimum at just under full power and continually rise as power drops. Recently I've see pp ss amps with 0.1% distortion at 0.1W (these are some pretty expensive amps in Stereophile). A few years ago There were plenty of pp ss amps that his closer to 1% at 0.5W and .01% or lower at just under full power. Of course, those amps were rated at, say 100W, .01% distortion. At any other power, the distortion was higher.

Leo

KT661.pdf

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On 6/30/2005 12:30:01 PM leok wrote:

... Crossover distortion is a strong characteristic at low powers in many pp ss amps ...

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Greetings,

I found your info on crossover distortion to be very interesting. Most guitarists (myself included) like distortion coming from our guitar amps. And for many years manufacturers have been making "stomp boxes" that enhance the amp's own natural distortion. Most of these devices -- whether they be called "fuzz", "overdrive" or "distortion" boxes -- generate some manner of even-order harmonics.

However, a small company called Z-Vex has developed a unit specifically designed to generate crossover distortion. The unit, called The Machine, has a sound which is so *pervasive* it can even cut through the even-order distortion from a fuzz-box and stand out. (You can hear sound samples of this unit compared to their other stomp boxes at http://www.zvex.com/effects.html 2.gif)

If this quality applies to the crossover distortion coming from a home audio amp, it's easy to appreciate how many listeners might have less tolerance for crossover distortion than even-order harmonic distortion.

Of course, another type of distortion I've heard about is intermodulation distortion (although I don't know whether this is different from crossover distortion...).

Take care,

Scott

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scotbuck,

Isn't that something. Any "defect" can be a feature. I'll bet the crossover distortion cuts through. I hadn't been aware of the fuzz boxes that will produce mostly even harmonics .. not easy to do. So, I guess you keep the ss amp out of trouble and let the fuzz-box "clip" first and get a tube-like overdrive sound. Is that correct?

Leo

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Paul,

I just realized you might have thought I was saying my SET is always below .03% distortion. No, the inverse. Possibly low level harmonics and hall reverb. approach that, and that is important for what I want out of some recordings.

Leo

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On 6/30/2005 7:15:58 PM leok wrote:

scotbuck,

Isn't that something. Any "defect" can be a feature. I'll bet the crossover distortion cuts through. I hadn't been aware of the fuzz boxes that will produce mostly even harmonics .. not easy to do. So, I guess you keep the ss amp out of trouble and let the fuzz-box "clip" first and get a tube-like overdrive sound. Is that correct?

Leo

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Greetings,

Actually, a fuzz works best when the amp is relatively clean. Early models using germanium transistors can be heard in the mid-to-late sixties on songs such as "Satisfaction" (Maestro fuzz), all of Jimi Hendirix's early material (Fuzz Face) and Led Zeppelin I (Sola Sound Tone Bender Mk II Pro). By contrast, others would use a germanium "treble booster" which gave a (relatively) clean boost to the mid-to-upper frequencies to overdrive your tube amp (think early Tony Iommi and Brian May). Each used the same transistors to a very different -- but equally tasty -- effect.

Later, partly due to the instability of the germanium transistors, manufacturers switched to silicone-based fuzz boxes and overdrives. These overdrives had even-order harmonics, but in a limited manner. Early examples were the Ibanez Tube Screamer model TS-808 (think Stevie Ray Vaughn) and the Boss OD-1 overdrive; I find that these sound best when the amp is already working hard and you use these to "go to 11". Also, distortion pedals -- which kinda fit between an overdrive and a fuzz -- appeared. One very popular model was the MXR Distortion + (think Randy Rhodes) and later the Boss DS-1 distortion (think Steve Vai); I find my amp can be a little distorted on its own to use these.

I read in a book detailing The Beatles' studio work that George Martin was somewhat taken aback when they were experimenting with early fuzz boxes. I don't think the band used any such device until Paul McCartney used one on his bass for the song "Think for Yourself" off of the Rubber Soul LP. Like you said, it's interesting that something which was considered a flaw could be so well used (even the "dukes of distortion" at Marshall amps used to advertise "100 watts of clean, undistorted power" ... NOT!!!) A lot of rock fans are glad they were sooooooo wrong! 2.gif2.gif2.gif

Take care,

Scott

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You bring up an excellent point Paul.

When HK measured their THD on their old, 70s, X30 units, they provided a figure that was indicative of the highest THD from 250 MILLAwatts up to full-rated power and from 20hz to 20khz. Although they didn't specifically say what the THD was at 1 watt, the given range was ample enough to let you know that the power down low (as low as 250 millawatts) was no higher then the THD figure quoted.

This, to me, was a nice gesture when you consider many makers of SS equipment quoted (and still do) THD figures at full-rated output, and at a single frequency (usually 1khz).

SS equipment seems to have gotten a bad reputation due to its inability at levels of 1 watt or less to deliver the THD that's posted by their makers at full-rated power and at 1khz. And when you consider that most heritage speakers are often run at 1 continuous watt or less (not including transients, or peaks obviously) it's no longer a head-scratcher to me why most SS amps don't sound as "clean"-at "normal" listening levels-as a lot of tube amps do.

-H2G

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