Does a little tube distortion really matter?

[tube fanatic]

I jotted down some random thoughts about points raised by FJD in some of the threads we have going.  Although Jean Hiraga is well known for his promotion of SETs, the interest in that mode was present all along but promoted on more of a local level.  I knew guys back in the 60s who were big proponents of the mode (myself included), especially with the numerous high efficiency speakers available (Klipsch being the most popular).  Commercial availability, of course, was another matter.

As far as higher order harmonics go, with any triode (not just the 45 or 2A3), those are such a tiny percentage of the tube's output that I don't personally even think about them.  Even the usual standard of 5% 2nd harmonic distortion at full output represents a very small part of the signal voltage.  Remember also that triodes have the advantage of decreasing distortion as the load impedance increases.  So when you look at a speaker's impedance curves, and see that it may go as high as 30 or 40 ohms at some frequencies, remember that distortion will be way down at those same frequencies (along with decreased power output as well).  Also, the 2nd harmonic distortion is responsible for a small rise in plate current at maximum (vs. quiescent) signal output.  That, too, decreases distortion slightly.  The last point is that a SET can be designed for a very low overall distortion profile (and this applies to actual triodes, whether directly or indirectly heated, or pentodes/beam power tubes which are triode strapped).  If we consider, for example, that the minimum impedance the amp will "see" is 4 ohms, we can design for a maximum of 5% second harmonic distortion at that load impedance.  In so doing we know that the distortion will be lower across the rest of the audio band in which the impedance will be higher.  This is good!

One comment about SEPs, which often have a total harmonic distortion of 10-12% at full output.  Using negative feedback (a necessity with single pentodes and beam power tubes) can bring distortion down to very low levels which allows them to rival triodes when presented with the varying speaker load impedance.  I've been on the fence "forever" about this as each tube type has some definite advantages.  At this point, I would not want to give up either, and switch between them depending on my mood!  I've also done a number of switchable amps which allow either mode to be selected depending on listener taste.

Tubes need to be experienced in order to formulate a conclusion.  I encounter few non-audiophiles who tell me that they like the sound of solid state better than the tube amps I demonstrate.  I'll relate such an experience with a 25 year old musician in a future thread.

Maynard

[Ski Bum]

I would posit that for many of us, a little tube distortion is the whole point.  This will invariably irritate some, using a tube amp as a processor/tone control.  Que sera sera.  Seriously, think of the expense involved in tube amps that perform well per prevailing engineering orthodoxy.  It would inevitably be a large, pp type, employing many parts, many tubes, and with enough complexity to meet the design goals.  It would be expensive, even on the DIY side, just due to parts count, not to mention the degree of expertise/time/education required as a prerequisite for all that.  And you end up with something akin to, say, an Audio Research amp, that is audibly indistinguishable from any old mainstream solid state amp.  That seems like a lot of effort just to end up where you started.

 

Regarding the higher harmonics, keep in mind that as the tube amps clip the third through about the seventh harmonic play a role in the tonal coloration/compression effects that these devices exhibit.  A monotonic harmonic pattern (characteristic of SE types) slips by the ear as it's perceived as added loudness and edge.  Of course gross clipping that excites higher harmonics than that sounds awful.

Edited August 10, 2015 by Ski Bum

[Guest thesloth]

I jotted down some random thoughts about points raised by FJD in some of the threads we have going.  Although Jean Hiraga is well known for his promotion of SETs, the interest in that mode was present all along but promoted on more of a local level.  I knew guys back in the 60s who were big proponents of the mode (myself included), especially with the numerous high efficiency speakers available (Klipsch being the most popular).  Commercial availability, of course, was another matter.

As far as higher order harmonics go, with any triode (not just the 45 or 2A3), those are such a tiny percentage of the tube's output that I don't personally even think about them.  Even the usual standard of 5% 2nd harmonic distortion at full output represents a very small part of the signal voltage.  Remember also that triodes have the advantage of decreasing distortion as the load impedance increases.  So when you look at a speaker's impedance curves, and see that it may go as high as 30 or 40 ohms at some frequencies, remember that distortion will be way down at those same frequencies (along with decreased power output as well).  Also, the 2nd harmonic distortion is responsible for a small rise in plate current at maximum (vs. quiescent) signal output.  That, too, decreases distortion slightly.  The last point is that a SET can be designed for a very low overall distortion profile (and this applies to actual triodes, whether directly or indirectly heated, or pentodes/beam power tubes which are triode strapped).  If we consider, for example, that the minimum impedance the amp will "see" is 4 ohms, we can design for a maximum of 5% second harmonic distortion at that load impedance.  In so doing we know that the distortion will be lower across the rest of the audio band in which the impedance will be higher.  This is good!

One comment about SEPs, which often have a total harmonic distortion of 10-12% at full output.  Using negative feedback (a necessity with single pentodes and beam power tubes) can bring distortion down to very low levels which allows them to rival triodes when presented with the varying speaker load impedance.  I've been on the fence "forever" about this as each tube type has some definite advantages.  At this point, I would not want to give up either, and switch between them depending on my mood!  I've also done a number of switchable amps which allow either mode to be selected depending on listener taste.

Tubes need to be experienced in order to formulate a conclusion.  I encounter few non-audiophiles who tell me that they like the sound of solid state better than the tube amps I demonstrate.  I'll relate such an experience with a 25 year old musician in a future thread.

Maynard

 

 

Hello Maynard,  I would like to go over the numbers for your analysis on SET behaviour. You have been at this a lot longer than I have so it would be nice if you could shed some light on the subject for me as well as others. Lets use the 2A3 for example with a 2k5:8 output transformer. Going with the datasheet to make life easier we have Vp=250, Ip=60mA, gm=5.25mA/V, mu=4.2, Rp=800. We know the impedance ratio of the output transformer is 2k5:8 or 2500/8=312.5  We also know the plate resistance of the 2A3 is 800, so the output impedance is roughly 800/312.5=2.56 ohms plus the DC resistance of the secondary so lets just say 3 ohms output impedance. The thevenin equivalent of the output would then be a perfect voltage source with 3 ohms in series with the load, now we have a potential divider created by the output impedance and the load impedance. We will use your speaker example of minimum impedance of 4 ohms and a maximum of 30 ohms as we know speaker impedance is all over the place dependant on frequency. For the perfect voltage source we will use 10 volts to make the math easy to follow, we will calculate how much voltage will be across the driver and hence the amount of distortion. So say @ 100Hz the speaker is at 4 ohms we can calculate how much voltage is across the speaker: (4/(4+3))*10=5.7V  so with 5% second order distortion we will have .05*5.7=.285V @ 200Hz. So the fundamental frequency is 100Hz voltage is 5.7V, second order distortion is 200Hz and there will be .285V across the driver. Now lets look at the higher frequencies. Say at 10kHz the speaker impedance is now 30 ohms, voltage across the speaker is now (30/(30+3))*10=9V That's almost double the voltage across the driver than @ 100Hz. So the fundamental frequency of 10kHz has 9V across the driver and the second harmonic distortion @ 20kHz is .45V.

 

Do I have this wrong? Because to me it looks like quite the opposite.

Edited August 10, 2015 by thesloth

[Paducah Home Theater]

I would posit that for many of us, a little tube distortion is the whole point.

I thought that was the whole point, period.

[Guest thesloth]

 

I jotted down some random thoughts about points raised by FJD in some of the threads we have going.  Although Jean Hiraga is well known for his promotion of SETs, the interest in that mode was present all along but promoted on more of a local level.  I knew guys back in the 60s who were big proponents of the mode (myself included), especially with the numerous high efficiency speakers available (Klipsch being the most popular).  Commercial availability, of course, was another matter.

As far as higher order harmonics go, with any triode (not just the 45 or 2A3), those are such a tiny percentage of the tube's output that I don't personally even think about them.  Even the usual standard of 5% 2nd harmonic distortion at full output represents a very small part of the signal voltage.  Remember also that triodes have the advantage of decreasing distortion as the load impedance increases.  So when you look at a speaker's impedance curves, and see that it may go as high as 30 or 40 ohms at some frequencies, remember that distortion will be way down at those same frequencies (along with decreased power output as well).  Also, the 2nd harmonic distortion is responsible for a small rise in plate current at maximum (vs. quiescent) signal output.  That, too, decreases distortion slightly.  The last point is that a SET can be designed for a very low overall distortion profile (and this applies to actual triodes, whether directly or indirectly heated, or pentodes/beam power tubes which are triode strapped).  If we consider, for example, that the minimum impedance the amp will "see" is 4 ohms, we can design for a maximum of 5% second harmonic distortion at that load impedance.  In so doing we know that the distortion will be lower across the rest of the audio band in which the impedance will be higher.  This is good!

One comment about SEPs, which often have a total harmonic distortion of 10-12% at full output.  Using negative feedback (a necessity with single pentodes and beam power tubes) can bring distortion down to very low levels which allows them to rival triodes when presented with the varying speaker load impedance.  I've been on the fence "forever" about this as each tube type has some definite advantages.  At this point, I would not want to give up either, and switch between them depending on my mood!  I've also done a number of switchable amps which allow either mode to be selected depending on listener taste.

Tubes need to be experienced in order to formulate a conclusion.  I encounter few non-audiophiles who tell me that they like the sound of solid state better than the tube amps I demonstrate.  I'll relate such an experience with a 25 year old musician in a future thread.

Maynard

 

 

Hello Maynard,  I would like to go over the numbers for your analysis on SET behaviour. You have been at this a lot longer than I have so it would be nice if you could shed some light on the subject for me as well as others. Lets use the 2A3 for example with a 2k5:8 output transformer. Going with the datasheet to make life easier we have Vp=250, Ip=60mA, gm=5.25mA/V, mu=4.2, Rp=800. We know the impedance ratio of the output transformer is 2k5:8 or 2500/8=312.5  We also know the plate resistance of the 2A3 is 800, so the output impedance is roughly 800/312.5=2.56 ohms plus the DC resistance of the secondary so lets just say 3 ohms output impedance. The thevenin equivalent of the output would then be a perfect voltage source with 3 ohms in series with the load, now we have a potential divider created by the output impedance and the load impedance. We will use your speaker example of minimum impedance of 4 ohms and a maximum of 30 ohms as we know speaker impedance is all over the place dependant on frequency. For the perfect voltage source we will use 10 volts to make the math easy to follow, we will calculate how much voltage will be across the driver and hence the amount of distortion. So say @ 100Hz the speaker is at 4 ohms we can calculate how much voltage is across the speaker: (4/(4+3))*10=5.7V  so with 5% second order distortion we will have .05*5.7=.285V @ 200Hz. So the fundamental frequency is 100Hz voltage is 5.7V, second order distortion is 200Hz and there will be .285V across the driver. Now lets look at the higher frequencies. Say at 10kHz the speaker impedance is now 30 ohms, voltage across the speaker is now (30/(30+3))*10=9V That's almost double the voltage across the driver than @ 100Hz. So the fundamental frequency of 10kHz has 9V across the driver and the second harmonic distortion @ 20kHz is .45V.

 

Do I have this wrong? Because to me it looks like quite the opposite.

 

 

 

Hello Maynard, rough morning over here. I figured it out. I wasn't calculating power, I was just looking at the voltage.

 

(5.7^2)/4=8.12 watts

 

(9^2)/30=2.7 watts

[Guest thesloth]

BTW sorry I kind of got off topic a little and didn't answer the question.

 

I think for recording and mixing (studio use) it is very important for the output of an amplifier to be as close to the input as possible, so yes as little distortion as possible. I don't think it is hard at all to design a tube amp with very low distortion, feedback is a very useful tool. Remember triodes have "internal feedback" so the argument of feedback is bad is moot. Triodes (most) are very linear devices and can have low enough distortion to not have to use feedback. I think anything <1% is inaudible.

 

So for playback in most cases there is nothing wrong with distortion as long as it's  kept low, I hold my limit to 5%. Remember with all these .0005% distortion SS amps with huge power driving speakers, the more power through the speakers the more SPEAKER distortion you get, and trust me it's a lot more then the 5% the SET amp puts out. High powered listening with solid state will actually yeild more distortion to your ears IMHO.

 

Give me tubes all day long

[juniper]

Maynard, from people I trust who heard Jean Hiraga's speakers at the high end show in  Munich in 2009, he is a wizard of some form..... Search for his secrets, I am sure you know most of them, some have said at this show in 2009, his set up was the best.   Against very expensive systems, he took some Altec 604 8g's and made them shine.  Crazy thing is, he was going against speakers in the hundreds of thousands dollar range.... Jean is a master...

Edited August 10, 2015 by juniper

[tube fanatic]

Maynard, from people I trust who heard Jean Hiraga's speakers at the high end show in  Munich in 2009, he is a wizard of some form..... Search for his secrets, I am sure you know most of them, some have said at this show in 2009, his set up was the best.   Against very expensive systems, he took some Altec 604 8g's and made them shine.  Crazy thing is, he was going against speakers in the hundreds of thousands dollar range.... Jean is a master...

Pat, I'm not in his league!!!  But, I keep trying .  If I live long enough perhaps I'll get there.......

 

Maynard

[juniper]

 

Maynard, from people I trust who heard Jean Hiraga's speakers at the high end show in  Munich in 2009, he is a wizard of some form..... Search for his secrets, I am sure you know most of them, some have said at this show in 2009, his set up was the best.   Against very expensive systems, he took some Altec 604 8g's and made them shine.  Crazy thing is, he was going against speakers in the hundreds of thousands dollar range.... Jean is a master...

Pat, I'm not in his league!!!  But, I keep trying .  If I live long enough perhaps I'll get there.......

 

Maynard

 

Don't know about that, I think of you as DR. of some form, your prescription for my amps..... worked out perfectly...

[Luv_sum_Horns]

Distortion? Not hearing it.

[moray james]

the amount of distortion is not the issue it's the order and the kind, that's why small simple tube amps can sound sound so so good. They (tubes)are about ten time more linear than a SS device so you don't have to mess with the circuit to fix them up like you do a SS circuit.

[Luv_sum_Horns]

Steve Deckert explains his take on why SETs sound so good on the Decware website. Basically that all instruments produce even order harmonics, except a couple of percussive instruments (like a xylophone) which produce very complex harmonics. Even order harmonics tend to reinforce the fundamental note, and odd order harmonics are detrimental to the fundamental note. SET amps also produce even order harmonics. You loose some of that with a PP, and solid state produces odd order harmonics!

 

I have no electronics training, and no musical talent and I have to rely on my ears. What I am hearing for the first time, is instruments that sound absolutely real and the notes and ensuing harmonics of each instrument sound true from attack to decay.

 

Here is the big difference between SS and tubes that I have noted: When I sat down for some critical listening with my SS hardware, I would find myself doing other things (very uninvolving). When my tubes are lit, I can't even get chores done as I find myself sitting down and enjoying music for hours on end.

[WMcD]

Gee, I wish I had saved things from the early days of the Internet and not misplaced an important book by John Pierce. 

 

Perhaps the good fellows here can confirm things or add thoughts.

 

FWIW:

 

I believe one fellow had written a master's thesis showing that our ears like second harmonic distortion (which is an octave above the fundamental) making at least some music sound warm.  He found correlation between tube amps and second harmonics and perceived favorable sound.

 

The following is some thing I can't retrace.  It is that Harry Olson or some big name had found that our ears, internally, produce second harmonics which increase with level.  But our brains filter them out so some extent while also using them to better perceive the fundamental.  It might have been the publication of John Pierce, who worked on Telstar..

 

This is somewhat related to the fact that if you sound a bass note, and it has even order harmonics, these line up with a major chord two octaves above.  So if we want to create the illusion of a bass note, we inject a major chord two octaves above.  Our brain thinks, there is a bass note down there someplace.

 

I know this is getting weird. 

 

My thought was that many speakers are like musical instruments and produce second harmonics, and others.  But  the K-Horn are free from these and so can sound harsh when fed by amps which are actually very accurate and free from distortion products.

 

This is somewhat related to my quip about claims that "all amps sound the same."  The subject of some ridicule. My thought is that all perfect amps must sound the same, even if we don't like them.

 

So . . . my thought is that K-Horns can sound harsh with perfect amps.  But if we can use amps with only second harmonics, our ear likes things better. 

 

Going further.  There could be a particular case when at high SPLs, our ear creates greater harmonics and "senses" bass or even mid freq sounds. 

 

But at low SPLs our ears produce lower harmonics and can't tell quite as well what is going on.  In this latter instance, we might benefit if the amp introduces harmonics, or the right harmonics.  Then the K-Horns seem more accurate.

 

WMcD

[derrickdj1]

All systems have non-linearity and intermodulation distortion and stored or build up of bass frequencies can be more bothersome than harmonic distortion. Maynard, can you give a perspective on this compared to harmonic distortion?

[Ski Bum]

Derrick, some excerpts from an old but valid paper about the harmonic distortion as it relates to tube amp coloration:

 

The second and third harmonics are the most important from the viewpoint of the electronic distortion graphs in the previous section. Musically the second is an octave above the fundamental and is almost inaudible; yet it adds body to the sound, making it fuller. The third is termed quint or musical twelfth. It produces a sound many musicians refer to as "blanketed." Instead of making the tone fuller, a strong third actually gives the sound a metallic quality that gets annoying in character as its amplitude increases. A strong second with a strong third tends to open the "covered" effect. Adding the fourth and fifth to this changes the sound to an "open horn" like character.

The higher harmonics, above the seventh, give the tone "edge" or "bite." Provided the edge is balanced to the basic musical tone, it tends to reinforce the fundamental, giving the sound a sharp attack quality. Many of the edge harmonics are musically unrelated pitches such as the seventh, ninth, and eleventh. Therefore, too much edge can produce a raspy dissonant quality. Since the ear seems very sensitive to the edge harmonics, controlling their amplitude is of paramount importance. The previously mentioned study of the trumpet tone [6] shows that the edge effect is directly related to the loudness of the tone. Playing the same trumpet note loud or soft makes little difference in the amplitude of the fundamental and the lower harmonics. However, harmonics above the sixth increase and decrease in amplitude in almost direct proportion to the loudness. This edge balance is a critically important loudness signal for the human ear.

RELATIONSHIP OF FACTORS AND FINDINGS

The basic cause of the difference in tube and transistor sound is the weighting of harmonic distortion components in the amplifier's overload region. Transistor amplifiers exhibit a strong component of third harmonic distortion when driven into overload. This harmonic produces a "covered" sound, giving a recording a restricted quality. Alternatively a tube amplifier when overloaded generates a whole spectrum of harmonics. Particularly strong are the second, third, fourth, and fifth overtones, which give a full-bodies "brassy" quality to the sound. The further any amplifier is driven into saturation, the greater the amplitude of the higher harmonics like the seventh, eighth, ninth, etc. These add edge to the sound which the ear translates to loudness information. Overloading an operational amplifier produces such steeply rising edge harmonics that they become objectionable within a 5-dB range. Transistors extend this overload range to about 10 dB and tubes widen it to 20 dB or more. Using this basic analysis, the psychoacoustic characteristics stated in the beginning of this paper can be related to the electrical harmonic properties of each type of amplifier.

Vacuum-tube amplifiers differ from transistor and operational amplifiers because they can be operated in the overload region without adding objectionable distortion. The combination of the slow rising edge and the open harmonic structure of the overload characteristics form an almost ideal sound- recording compressor. Within the 15-20 dB "safe" overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective head room that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass response is directly related to the strong second and third harmonic components which reinforce the "natural" bass with "synthetic" bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube preamplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.

[derrickdj1]

Thanks Ski Bum.  Learning a lot about tubes!

[tube fanatic]

Ski Bum, thanks for posting that very interesting article!  I have always questioned whether the higher order harmonics really matter.  Consider the case of 5% second harmonic distortion.  That represents only 1/400 of the output power of the fundamental frequency, and the higher order harmonics are even more miniscule.  Consider the case of an amp which is putting out, say, 2 volts into 4 ohms at its fundamental.  5% second harmonic distortion would then be 1/10 volt.  If we convert those numbers to power, we wind up with 1 watt out at the fundamental, and only .0025 watt out at the second harmonic.  If we consider the distortion created by the speakers, the amps seem benign in comparison.  I'm anxious to hear other views on this subject!

Maynard

[Fjd]

The entire article is from the Journal of The Audio Engineering Society, May 1973 and titled "Tubes Versus Transistors - Is There an Audible Difference" and was written by Russell O. Hamm of Sear Sound Studios in NY.

 

 

https://archive.org/details/TubesVersusTransistors-IsThereAnAudibleDifference

 

 

If anyone has trouble with the download options in the link above, Butler Audio, Inc. has also posted the article to its website at the link below.

 

 

http://www.butleraudio.com/tubesvstrans1.html

 

 

 

 

Derrick, some excerpts from an old but valid paper about the harmonic distortion as it relates to tube amp coloration:

 

The second and third harmonics are the most important from the viewpoint of the electronic distortion graphs in the previous section. Musically the second is an octave above the fundamental and is almost inaudible; yet it adds body to the sound, making it fuller. The third is termed quint or musical twelfth. It produces a sound many musicians refer to as "blanketed." Instead of making the tone fuller, a strong third actually gives the sound a metallic quality that gets annoying in character as its amplitude increases. A strong second with a strong third tends to open the "covered" effect. Adding the fourth and fifth to this changes the sound to an "open horn" like character.

The higher harmonics, above the seventh, give the tone "edge" or "bite." Provided the edge is balanced to the basic musical tone, it tends to reinforce the fundamental, giving the sound a sharp attack quality. Many of the edge harmonics are musically unrelated pitches such as the seventh, ninth, and eleventh. Therefore, too much edge can produce a raspy dissonant quality. Since the ear seems very sensitive to the edge harmonics, controlling their amplitude is of paramount importance. The previously mentioned study of the trumpet tone [6] shows that the edge effect is directly related to the loudness of the tone. Playing the same trumpet note loud or soft makes little difference in the amplitude of the fundamental and the lower harmonics. However, harmonics above the sixth increase and decrease in amplitude in almost direct proportion to the loudness. This edge balance is a critically important loudness signal for the human ear.

RELATIONSHIP OF FACTORS AND FINDINGS

The basic cause of the difference in tube and transistor sound is the weighting of harmonic distortion components in the amplifier's overload region. Transistor amplifiers exhibit a strong component of third harmonic distortion when driven into overload. This harmonic produces a "covered" sound, giving a recording a restricted quality. Alternatively a tube amplifier when overloaded generates a whole spectrum of harmonics. Particularly strong are the second, third, fourth, and fifth overtones, which give a full-bodies "brassy" quality to the sound. The further any amplifier is driven into saturation, the greater the amplitude of the higher harmonics like the seventh, eighth, ninth, etc. These add edge to the sound which the ear translates to loudness information. Overloading an operational amplifier produces such steeply rising edge harmonics that they become objectionable within a 5-dB range. Transistors extend this overload range to about 10 dB and tubes widen it to 20 dB or more. Using this basic analysis, the psychoacoustic characteristics stated in the beginning of this paper can be related to the electrical harmonic properties of each type of amplifier.

Vacuum-tube amplifiers differ from transistor and operational amplifiers because they can be operated in the overload region without adding objectionable distortion. The combination of the slow rising edge and the open harmonic structure of the overload characteristics form an almost ideal sound- recording compressor. Within the 15-20 dB "safe" overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective head room that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass response is directly related to the strong second and third harmonic components which reinforce the "natural" bass with "synthetic" bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube preamplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.

Edited August 13, 2015 by Fjd

[Ski Bum]

Ski Bum, thanks for posting that very interesting article!  I have always questioned whether the higher order harmonics really matter.  Consider the case of 5% second harmonic distortion.  That represents only 1/400 of the output power of the fundamental frequency, and the higher order harmonics are even more miniscule.  Consider the case of an amp which is putting out, say, 2 volts into 4 ohms at its fundamental.  5% second harmonic distortion would then be 1/10 volt.  If we convert those numbers to power, we wind up with 1 watt out at the fundamental, and only .0025 watt out at the second harmonic.  If we consider the distortion created by the speakers, the amps seem benign in comparison.  I'm anxious to hear other views on this subject!

Maynard

I think it matters in proportion to how far down the watt scale you go.  I doubt I clipped my old Scott too much, it was a 20 watt amp.  Drop down to a 300b at 7 watts or so, and the chance of clipping goes up, and even more when you drop into the 2a3 and even smaller sweep tubes.  45s?  I think I would clip a one watt amp pretty easily.

 

I wouldn't be at all surprised if a Khorn playing below 95db contributes less distortion than many of these single ended amps.  

[muel]

as interesting as it was my eyes really hurt after reading that white on black text!  I still see the black lines wherever I look.