Talk:Valve sound

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Contents 1 Characteristics? 2 Soft clipping or compression? 3 Major Omissions 4 Harmonic series 5 Copyright material 6 Gain compression due to LS voice coil heating 7 From Valve amplifier page 7.1 'Audiophile amplifiers' 8 Output transformers 9 Audible differences 10 Accuracy in recording studios 11 Supposed reasons for valve sound 12 Canadian English 13 Topologies and distortion 14 Transfer characteristics of active devices 15 Plan to replace Supposed reasons for valve sound section 16 Are odd harmonics 'musical'? 17 Facinating reference 18 Links to milbert.com 19 Audible Differences 20 Most Guitarists cant tell tube amps from SS 21 Psychoacoustics 22 Class A push-pull amplifier

[edit] Characteristics?

I don't believe this has anything to do with triode characteristics. Valve amplifiers differ from transistor ones in a number of fundamental ways. The most obvious is the need for a final output transformer in valve systems which is not present in transistor designs. More subtle influences are the behaviour of valve circuits when handling signals outside the designed peformance where a transistor has a charactristic clipping effect whilst the valve is just non-linear.

An output transformer is not required in e.g. circlotron designs with multiple paralelled 6C33C valves; a single pair has 20 ohm output impedance without feedback, and 500mA DC current capability (about 2A peak, IIRC). Similarly, transformer coupled MOSFET and power JFET designs have been implemented. While the use of a transformer certainly contributes to the characteristics of typical valve amplifiers, it is not necessarily defining to the positive aspects of the sound.

As someone once stated, I like valve amplifiers despite their distortion, not because of it. This article should reflect that the valve enthusiasts are divided between those who like the "valve sound" as they call it, and those for whom valves are simply a better means to an end in some cases. You should have a look at the transfer curves at some point. Valves typically have a more euphonic harmonic overtone spectrum than BJT and MOSFET devices before feedback is applied.

Zuiram 05:28, 3 November 2006 (UTC)

In any event, triodes were not the dominant part of the amplifier as to handle the necessary power to drive the transformer it was necessary to use a pentode or pentode pair. Triodes do make up a good part of a pre-amplifier but audio buffs seem to prefer transistorised preamplifiers in conjunction with valved power amplifiers! Rjstott

Claiming that it is necessary to use pentodes to achieve sufficient output power makes no sense. The 6C33C glass triode can deliver about 10-15W single-ended or 60W push-pull class A, while the 3CX300A1 ceramic triode can deliver a few hundred watts push-pull class A. GM70 also springs to mind.

It is easier to make good solid state preamplifiers than to make good solid state power amplifiers, amongst other things because of higher availability of parts (2SK389/2SJ109 dual monolithic JFETs come to mind), and the ability to run things with a very high bias without needing a lot of heat sinking. That said, I've not noticed that particular trend. I have, however, noticed that many valve enthusiasts like passive, stepped-transformer based volume controls as "preamps".

Zuiram 05:28, 3 November 2006 (UTC)

I agree. Device transfer characterstic is not as important as circuit topology. Pentodes are very similar to FETs, so some audiophiles mistakenly assumed you could produce "tube sound" with FETs. There was a great article in the early 1990s in Electronic Design or EDN or something about this. The author had designed amplifers for Carver (Carvin?). He had successfuly reproduced tube sound with bipolar junction transistors. I remember calling him directly to talk about it. It was really interesting. I've been looking for that article ever since. Anyone know what I'm talking about?? Madhu 21:16, 8 November 2005 (UTC)

There is no doubt that the topology is important. But the device transfer characteristics should not be ignored either. Pentodes are indeed somewhat similar to MOSFETs, which is what I imagine you meant. Triodes, however, pretty much define the valve enthusiasts who want neutral sound, and until recently there were no reasonably priced solid-state equivalents of the triode.

At a higher price, you can have Sony VFETs (200V 5A 160W JFETs) that have even better linearity than triodes with the same general transfer characteristic. If you can live with a single polarity, such as when using balanced circuits, SRPP, followers or transformer coupling, then Lovoltech has a series of power JFETs designed for laptop power supplies (24V 100A 30W). The importance of the device transfer characteristic is easily demonstrated by using a simple circuit, such as the Son of Zen by Nelson Pass, and building it with different devices.

In short, the result is the sum of the parts, and device transfer characteristics, topology and power supply design are generally considered equally important by many notables, such as John Curl (Parasound, etc.) and Nelson Pass (Pass Labs, etc.).

Geeze, I'm sticking in tube sound and tube amplifier lest Americans not know what you're talking about. Ortolan88

[edit] Soft clipping or compression?

"A tube radio or tube amplifier will increase in volume to a point, and then as the volume is further increased beyond the linear range, it gently reduces in gain."

I'm pretty sure this isn't true. I think it just has soft limiting clipping, not audio level compression. - Omegatron 15:47, Feb 6, 2005 (UTC)

If it is true, it probably has more to do with a weak, unregulated power supply than anything else. Madhu 21:16, 8 November 2005 (UTC)

I think it is true. Its called gain compression in RF amps and such. Anyway whats the difference between soft limiting and gain compression?--Light current 15:08, 31 January 2006 (UTC)

"Gain compression" in RF amps is just non-linear distortion, or soft clipping. Here's a decent description: [1]

I would imagine tube audio amps don't do anything different. The only way I can think of that they could is if there were some element of the tube that was heated by higher signal levels and the resistance change from the heat also changed the gain?

I don't know enough about tubes or the circuits they live in. I thought only the filament got appreciably warm, though, and that isn't affected by the signal and doesn't affect the gain, as far as I know...

Oh, and the difference between clipping and audio level compression is that

• in clipping, the signal is distorted to keep it under a certain level, creating extra harmonics. Soft clipping just means there isn't a sharp "knee point" in the transfer characteristic, as the above gain compression article explains. A sine wave going through soft clipping would become more like a "smooth" square wave and have lots of extra harmonics.
• in compression, the gain of the circuit is actually changed in response to the level of the input over time, so the transfer function is linear as long as you're only looking at a short period of time. A sine wave in will look like a sine wave out, but the overall gain varies depending on the level of that sine wave. (Above a certain level, the output sine wave will always be the same amplitude.)
• "limiting" can mean either, apparently, so I crossed that out in my comment above and replaced it with clipping, which is the definition I meant. — Omegatron 15:35, 31 January 2006 (UTC)

Yes well i think we're in broad agreement on this. Its largely a matter of terminology. But to my knowledge, its the actual non linear characteristics of the device when run at high levels that causes the compression of gain. It happens in transistor RF amps too. I dont think its to do with heat altho' I could be wrong on that.--Light current 15:42, 31 January 2006 (UTC)

Simple enough.. At low currents, the slope is not very steep, at medium currents, the slope is linear and steep. At high currents, however, something interesting happens, which is not due to the valve itself. The output transformer has a significant AC impedance, and at high currents, the voltage drop over the output transformer becomes very significant, which lowers the plate voltage. At lower plate voltages, less current conducts.

Hence, it is the interaction between the transformer and the valve that give rise to this "soft" distortion characteristic.

I have an electrostatic headphone / valve driver combo, which does not use an output transformer (since the voltages involved are highish (+/- 350V IIRC) and the current is low (<10mA)). It does not have a soft clipping characteristic, since there is no output transformer.

Zuiram 05:28, 3 November 2006 (UTC)

Go read the article. It explains that "gain compression" is just non-linear distortion . — Omegatron 15:44, 31 January 2006 (UTC)

Yes its effect must be one of distortion, due to the nonlinearity of the transfer function which also, of course causes a loss of gain. So you get out less than you think you would if you took the small signal gain of the amp. Thers no problem here -is there?--Light current 04:09, 2 February 2006 (UTC)

Ahhh. Yes, it causes loss of signal level, but that's not "loss of gain". The gain of the circuit is still the same; it's just reached the max it can output for a given input. — Omegatron 16:06, 2 February 2006 (UTC)

I meant loss of 'slope' or 'differential' gain. ie we have gain compression. I use the term 'slope' as you would use it in 'slope resistance' for a diode etc.--Light current 17:10, 3 February 2006 (UTC)

Your argument is correct, however, many data sheets for RF amplifiers list gain compression rather than non-linear distortion simply because it's easier to measure. Further, in narrowband systems, the effect "looks" more like gain compression simply because the harmonics are filtered out. In wideband and low frequency systems, the non-linear effects are readily visible, e.g. the output is clipped. To see the same thing at 1 GHz, you would need an oscilloscope with a bandwidth of at least 10+ GHz. Yes, you could see it with a spectrum analyzer, but what you see is the fundamental compressed and the harmonics picking up. It's not as intuitive as time domain clipping. Madhu 18:33, 2 February 2006 (UTC)

Yeah, RF tube amps are from a very different world from audio tube amps. Is "gain compression" only relevant to AM? — Omegatron 19:18, 2 February 2006 (UTC)

I would say not. As you turn up the wick, with whatever sort of signal you have, you will get gain compression. Now maybe its the time for me to mention the fact that a transistor's operating point may move with temperature, so higher power o/p may lead to compression due to collector dissipation. Im not sure about a tubes operating point with output voltage. I would think it woudnt move much at all( theyre running damn hot as it is!!)--Light current 17:10, 3 February 2006 (UTC)

But it's not a change in gain; it's non-linear distortion. The output level stays relatively the same as the input level goes higher. Gain is a linear operation. — Omegatron 17:19, 3 February 2006 (UTC)

Reagardless of what its called, the output will look the same on an oscilloscope. Once you reach the non linear portion of the transfer characteristic of amy amplifier, any increase in input will not be matched by a proprtional increase in output. Thus we have compression of gain. Gain compression. Also, at this time becuase the transfer function is no longer linear, harmonic distortion will result. (Im not sure of your use of the term non-linear distortion-- do you have a reference? or link). I think this sums it all up dont you?--Light current 18:03, 3 February 2006 (UTC)

Yes, the term "non-linear distortion" is a little redundant, since all distortion is non-linear and all non-linearities cause distortion.

I agree with everything you said here, but I don't know why it's called "gain compression". It's just a matter of semantics, I'm sure. — Omegatron 19:39, 3 February 2006 (UTC)

Tube or transistor, gain compression means the same thing and is caused by clipping, soft or hard. Here's an article about it. It's relevant in any system with a wide dynamic range, audio or RF. Front end RF amps are as susceptible as any. Years ago, we added a low noise RF amp and directional antenna to a consumer 900 MHz receiver. We hoped to improve the transmission range. It worked, but it also picked up a couple of UHF stations around 700 MHz. Turns out, channel 54 was blasting 6 MW (yes Megawatts) of AM, FM, and PM our way. Our poor little RF amp, expecting -80 dBm, was way out of it's league and splattered mixing products all over the place. Needless to say, there was considerable gain compression going on. Madhu 00:50, 3 February 2006 (UTC)

I've been meaning to illustrate the clipping and compression articles with some waveforms, as I tried to do on the compression talk page. I think I know how to illustrate them now. Maybe I'll do that tonight. — Omegatron 15:48, 31 January 2006 (UTC)

So I was thinking I could illustrate the different concepts by showing a simple waveform in both a "wide view" to show the change in gain over time, and a "zoomed in view" to show how the waveform is either distorted or not distorted. Here's the example wave I am thinking of, but maybe someone has a better idea:

It's a mixture of 100 and 110 Hz sine waves, to get the beating effect (so that it has some structure visible from this "macroscopic" view but still looks like a sine wave up close), then I increased it linearly from left to right, so you can see as the clipping/compression kicks in. I'm sure there's a better way to show this, though, so I'm holding off on making all of the images/sound files for a bit until I get some other opinions. — Omegatron 02:34, 2 February 2006 (UTC)

A compressor is a bit like an AGC circuit. As long as you have the right time constants, you wont cause much distortion on the output signal if the input signal amplitude is not changing too fast.--Light current 04:14, 2 February 2006 (UTC)

Yes, that's exactly how it works. — Omegatron 16:06, 2 February 2006 (UTC)

Im glad we agree on something!--Light current 18:55, 2 February 2006 (UTC)

Hooray! — Omegatron 19:18, 2 February 2006 (UTC)

[edit] Major Omissions

This acticle does not mention production and playback equipment in recording studios and that many producers with 'Golden ears' still prefer to do all the production (with real analog valve sound), including mixing down, prior to digitsation.

That is becoming rather rare, unfortunately. There are some places that still do it, though, like that recording studio which used to be a church and now does direct-to-disc vinyl recordings with valve equipment. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Harmonic series

I've heard these claims that even-numbered harmonics are "more musical" than odd-numbered, but I haven't seen a clear explanation. If the notes of the harmonic series are transposed down to stay within the octave, don't they all map to named notes? — Omegatron 02:40, 24 January 2006 (UTC)

The odd harmonics starting at the 5th are more offensive than the even ordered ones and the 3rd.

Someone (BBC?) did some experiments at one point in time and determined a weighting formula for the harmonic spectrum that correlated with subjective listening experiences in double blind trials. You could look that up.

2nd and 3rd order harmonics are generally not offensive, and at the levels present in linear circuits (even when operated open-loop, just about any simple audio circuit not using op-amps or other super-high-gain elements will generate <1% THD) are not audible in general.

Double blind experiments indicate no audible differences in a digital-sourced reference system when 2nd harmonic distortion is added until somewhat above 1%. For comparison, the threshold for the 7th harmonic is on the order of parts per million in the same experiment. This is part of the reason why there is a trend toward lower global negative feedback, as open-loop linear circuits generate a monotonically falling spectrum of harmonic overtones that is consistently porportional to the signal level, which closely mimics the distortion in our ear.

Zuiram 05:28, 3 November 2006 (UTC)

Not necessarily. Harmonics 2, 4, 8, 16 etc. are by definition named notes. If one assumes the frequency of each half step is given by:

where N is the step number (e.g. A is 0, A# is 2, B is 3, C is 4 etc) and Ao is the root note (440 Hz for A above middle C, I think). Every power of 2 is exactly an integer step, which is a named note. If you do the math, the 3rd harmonic is 19.02 half steps up. This one octave and 7.02 half steps. For example, the 3rd harmonic of C is between G and G#. The 5th harmonic is 27.863 half steps, or two octaves and 3.863 half steps. That's equivalent to C and something between D and D#. The 6th harmonic isn't great either, it's 31.02 half steps. 4th and 8th harmonics are precisely the same note one and two octaves up. Madhu 03:16, 26 January 2006 (UTC)

Hmm... I guess I was wrong.

Harmonic	Frequency	440 ≤ x < 880	Note name	Relationship
1	440	440	A4	unison
2	880	440	A4	unison
3	1320	660	E5	3:2 = perfect fifth
4	1760	440	A4	unison
5	2200	550	C#5	5:4 = major third
6	2640	660	E5	3:2 = perfect fifth
7	3080	770		7:4 = nothing?
8	3520	440	A4	unison
9	3960	495	B4	9:8 = major second
10	4400	550	C#5	5:4 = major third
11	4840	605		11:8 = nothing?
12	5280	660	E5	3:2 = perfect fifth
13	5720	715		13:8 = nothing?

I guess I never thought it through above the 6th.

In equal temperament, as you described, they're all going to be off, but the article said Just intonation. Still, though, in JI, the named notes are derived from the harmonic series, so I don't understand how any of the harmonics could be "unmusical". And, it seems, the offenders are really prime harmonics, so they're necessarily going to be odd. — Omegatron 05:22, 26 January 2006 (UTC)

2nd and 3rd are prime, and not generally offensive. A single-ended non-feedback valve amp, for example, will generate "exclusively" 2nd (from the valve) and 3rd (from the transformer) distortion. All dynamic loudspeakers generate significant (up to 30%) 2nd and 3rd harmonic distortion at normal listening levels. Push-pull type electrostatics generate only 3rd order (<1%).

Zuiram 05:28, 3 November 2006 (UTC)

This JI page considers 7/4 to be a minor seventh. And here's another:

The 7:4 ratio is the naturally occurring minor seventh that exists in the overtone series (approximately 31% of a semi-tone flat from the equal tempered minor seventh). [2] — Omegatron 19:40, 31 January 2006 (UTC)

Here's the root of the problem (pun intended): equal temperment results in irrational multpliers for notes. So by definition, it is not possible for any two notes (other than octaves) to be exact harmonics. We all know that irrational numbers cannot be written as the ratio of two integers, but in many cases, it's close enough (as your table shows). I think the problem with odd harmonics (and some even harmonics) is that they are too far from any "good" note. Based on this argument, I tend to think tuning a guitar using frets might be more accurate than tuning using harmonics. This assumes the frets are placed precisely. In reality it probably doesn't matter all that much. I heard many "goldean ears" suggest that electronic tuners are not accurate -- I think the opposite is true. They are too accurate! If you tune an instrument based on good quality sound, it probably is not in precise equal temperment. Just my $0.02 Madhu 16:36, 26 January 2006 (UTC)

Well, yes, that's Just intonation (pure harmonic relationships) vs equal temperament (equally spaced intervals), but regardless of which you pick, it seems the prime number harmonics above 7 don't map to any of the 12 standard musical notes (exactly or approximately).

Is this important to the sound of distortion? I don't know. — Omegatron 16:58, 26 January 2006 (UTC)

That's the real question. My guess is that many harmonics are not pleasing, but the even/odd harmonic issue is probably as much rumor as reality. I think it's safe to say that there are so many differences between tubes and transistor amps that it's not exactly clearcut. Madhu 03:14, 27 January 2006 (UTC)

The even/odd issue started out as a rule of thumb, and unfortunately stuck.

The difference in harmonic spectra is relevant, but many people who use the terms "valve sound" and "transistor sound" are basing their comparisons on stuff from both camps that is far from state of the art. They feature differences that primarily result from design philosophy differences and the constraints associated with each device. The actual intrinsic differences only become clear once you compare state of the art (by which I do not mean "most expensive") equipment from each camp.

Zuiram 05:28, 3 November 2006 (UTC)

I think you are correct 'O' about the 7th, 11th and 13th harmonics not mapping to any of the 12 standard musical tones. Hence the problem of tuning painos. On a stretched string, the seventh harmonic (more strictly 'partial') is, for some reason, out of tune with the others. I think its slightly flat and therefore the notes have to be tweaked up slightly. Its all a compromise tho'. Do we really need to consider what happens above the seventh harmonic in valve sound?--Light current 23:52, 28 January 2006 (UTC)

In single ended triode, you can disregard the seventh, as it simply doesn't occur at any relevant levels. In push-pull pentode, at the other end of the spectrum, you'll see a fair bit of the seventh. Zuiram 05:28, 3 November 2006 (UTC)

Even your tender ears wont hear the 7th harmonic of 3kHz!--Light current 23:53, 28 January 2006 (UTC)

The 7th harmonic of 3kHz is 21kHz, which is outside the hearing range of the general population due to incremental hearing loss with age. It is, however, not inaudible to fairly young listeners that have taken good care of their ears.

More relevantly, you'll definitely hear the 7th harmonic of 30Hz, which is 210Hz, at which point your ears are about 20dB more sensitive, meaning that even 0.1% 7th harmonic will sound like 10%. And, considering that about 50% of the audio power is in the band below 315Hz, it is easy to see how higher order distortion can "stick out" higher up.

Our ears are mainly phase sensitive below 1250Hz, meaning the low order distortion does not generally impact the sense of realism as much in that range. They are, however, mainly level sensitive above 1250Hz, meaning that the high order overtones of the high-power range end up in the most level-sensitive part of our hearing. Most valve designs avoid this.

Zuiram 05:28, 3 November 2006 (UTC)

No, the harmonics are perfect by definition. They are always in tune with each other because they're a perfect mathematical relationship. That's what I don't understand about them being "unmusical". I don't think it's possible for perfect harmonics to be "unmusical", since musical intervals are based on the harmonic series.

Consonance depends on the smallest period that is common between two waveforms. The sum of a 200 Hz waveform and a 300 Hz waveform added together repeat every 100 Hz, which is pretty consonant (a perfect fifth). A 200 Hz and 205 Hz waveform will have an audible beat frequency at 5 Hz, and are quite dissonant. A 100 Hz and its 7th harmonic, 700 Hz, would cycle at 100 Hz. I don't know how you can be more consonant than a harmonic.

As for pianos, the strings are not ideal (they are stiff, three dimensional, elastic, and so on), so the harmonics generated are not perfect. All of the harmonics on a real stringed instrument are slightly sharp from the ideal mathematical harmonics. (They become "inharmonic partials", though they are usually just considered harmonics since they're "close enough".) There's no analogous mechanism for harmonic distortion, so all the harmonics are exact multiples of their fundamental.

Yes, we do need to consider what happens to the harmonics in valve sound, simply because valve enthusiasts use it in their arguments. Besides, you can hear the 7th harmonics of every sound below ~3 kHz. — Omegatron 02:21, 29 January 2006 (UTC)

Most Perfect harmonics wont be unmusical, but in the equal tempered tuning system, most of the notes are inaccurate anyway so their harmonics sound bad against other notes in the eqaual tempered scale.See table below. Also, as said above I think some instruments dont produce perfect harmonics when you go higher up.

If the first 15 harmonics are transposed into the span of one octave, they approximate some of the notes in what the West has adopted as the chromatic scale based on the fundamental tone. The Western chromatic scale has been modified into twelve equal semitones, and in relation to that scale, many of the harmonics are slightly out of tune, and the 7th, 11th, and 13th harmonics are significantly so. In the late 1930s, composer Paul Hindemith ranked musical intervals according to their relative dissonance based on these and similar harmonic relationships.

Below is a comparison between the first 20 harmonics and their equivalent frequencies in the 12-tone equal-tempered scale. Orange-tinted fields highlight differences greater than 5 cents, which is the "just noticeable difference" for the human ear. (Because physical characteristics of musical instruments cause significant variations from these theoretical values, they should not be used for tuning without adjusting for those variations.)

---

Harmonic Note Variance 1st C1 0 cents 2nd C2 0 cents 3rd G2 +2 cents 4th C3 0 cents 5th E3 −14 cents 6th G3 +2 cents 7th Bb3 −31 cents

Harmonic Note Variance 8th C4 0 cents 9th D4 +4 cents 10th E4 −14 cents 11th F4 −49 cents 12th G4 +2 cents 13th A4 +41 cents 14th Bb4 −31 cents

Harmonic Note Variance 15th B4 −12 cents 16th C5 0 cents 17th C#5 +5 cents 18th D5 +4 cents 19th D#5 −2 cents 20th E5 −14 cents

--Light current 02:45, 29 January 2006 (UTC)

What does equal temperament have to do with anything? The article is talking about Just intonation and harmonic distortion. — Omegatron 03:01, 31 January 2006 (UTC)

So you wanna talk JI eh? OK. Quote from article:

It is interesting to note that in the harmonic series even harmonics always tend to correspond to a named note (in Just Intonation) relative to the fundamental, whereas (SOME) odd harmonics do not (take for example the 7th, 11th and 13th harmonics).

So by your own table above, the 7th, 11th, and 13th harmonics are not musical 'cos they dont correspond to any of the other notes in the scale (major, minor,pentatonic or whatever). So the sentence should be modifed as above to be correct. Understand?--Light current 04:10, 31 January 2006 (UTC)

It is interesting to note that the 7th harmonic (7/4 ratio or 14/8) is nearly (but not quite) equivalent to a major 7th (15/8). It will of course sound flat. So it would appear I was right before -- strange but true! --Light current 04:36, 31 January 2006 (UTC)

Just found this on the web:

For a note C, an octave below middle C, the first 10 harmonics in the chord of nature would be: (image of stave with some notes appeared here) The accidental on the note B is a contemporary '3/4 flat' sign. This is included because the 7th harmonic is rather flat, making the chord of the first 8 harmonics a dominant seventh with an 'out of tune' seventh. When sound comes from a source that is not perfectly periodic, the chord of nature may still be inherent in the sound, but the chord will be slightly 'imperfect'. Musical strings are sources whose motion is generally very close to being periodic, so the chord of nature is clearly recognisable as inherent in their tone. If a sound source is not perfectly periodic, the 'pure tones' are then not true harmonics with frequencies arranged in the harmonic series, but may nevertheless be very close to this. Rather than 'harmonics', they are properly called partials. Any musical tone with a definite pitch can be 'diffracted' into partials, usually arranged in the Chord of Nature, much as white light can be diffracted into colours of the rainbow. The component simple tones within the Chord are beautiful to behold, and stand at the threshold of the inner world of sound. Although the 7th harmonic or 7th partial is 'out of tune' by the standards of Western tonality, there is nothing 'wrong' with it. It is, in fact, absolutely perfect in its relationship to the other partial or harmonic tones - but to hear this one has to be free of the expectations brought about by Western musical conditioning.

So maybe I was right after all! --Light current 04:55, 31 January 2006 (UTC)

Yes. That's what I just said. — Omegatron 15:18, 31 January 2006 (UTC)

Yeah, but from a western musicians POV, the 7th harmonic will sound out. Which is why, as I mentioned earlier, piano tuners may have to tweak some notes just a teeny bit sharper to get the right sound. After all, its the highest partial that grabs most of our attention in a note (assuming you can hear it!)--Light current 15:49, 31 January 2006 (UTC)

Theres something still not quite right here. On one page (WP) I read that the 7/4 ratio is sort of half way between a minor 7th and a major seventh. Now to me, both of these intervals would sound harmonious. (I prefer the major seventh myself as I think its more jazzy and of course in not a dominant seventh chord). So if people are talking about the interval sounding flat, they must be talking of the major 7th. 7/4 sounds sharp in relation to the minor seventh. So what the hell are people talking about when they say seventh? Major seventh or minor seventh: that is the question.--Light current 22:09, 31 January 2006 (UTC)

[edit] Copyright material

A large portion of this article seems to have been copied en bloc from [3]. I shall remove it all--Light current 03:55, 1 February 2006 (UTC)

[edit] Gain compression due to LS voice coil heating

I have recently been reading about the gain compression that takes place due to loudspaeker voice coils heating up and incresasing their resistance. This causes less power to be drawn from the amplifier and a reduction in SPL. Maybe we need a separate article purely on Gain compression. Any thoughts?--Light current 00:23, 2 Feb 2006 (UTC)

The voice coil heating phenomenon is well-known in pro audio circles, but not very well known in hi-fi circles. JBL 2226, for example, a 12" pro woofer, is rated at 3dB power compression at 600W, which is an exceptionally good figure. Most home audio drivers will have more than 3dB power compression at one tenth of that.

Zuiram 05:28, 3 November 2006 (UTC)

Does that have any real effect? As we've mentioned elsewhere, the output impedance of a loudspeaker amplifier is made very low, a bridging connection, so that the amplifier can counteract any such effects.

Yes, gain compression obviously needs an article. — Omegatron 19:39, 3 February 2006 (UTC)

The output impedance of the amplifier should be high to counteract that. The motion of the cone is proportional to the current through the voice coil. As the resistance of the voice coil has a positive temperature coefficient, the heating causes the resistance to increase, causing less current to be drawn for a given voltage.

Yes, a voltage driven loudspeaker (most of the ones out there) will need a low impedance source (or compensation of some sort) to control the system resonance. That is the reason for voltage-driven loudspeakers (rather than current-driven) and for voltage-output amplifiers (rather than current-output).

In fact, using current output and a biquad transform to handle the resonance, you generally reduce the distortion by approximately one order of magnitude for a given loudspeaker driver. I could point you in the direction of the research if you speak technical Russion. I don't, I just have the links and got an executive summary from someone.

Incidentally, Steen Duelund (RIP) from Denmark did some work on this, and actually used resistive elements with a negative temperature coefficient in his passive crossover networks to compensate for this effect. Apparently to great effect in terms of both micro- and macrodynamics.

Zuiram 05:28, 3 November 2006 (UTC)

Yes it has effect, not on distortion necessarily, but on overall efficiency of the sound system and so is a form of gain compression.--Light current 19:43, 3 February 2006 (UTC)

Compression is a form of distortion. One that is particularly offensive to those who enjoy dynamic music, such as Jazz. Yes, it also has an effect on the system efficiency, but valves are not exactly known for their high efficiency.

Zuiram 05:28, 3 November 2006 (UTC)

[edit] From Valve amplifier page

To be merged into this article by authorised audiophiles. --Light current 17:22, 5 March 2006 (UTC)

[edit] 'Audiophile amplifiers'

For diverse reasons, Although valves are today an obsolete technicnology except for specialist applications, there has been a resurgence in the popularity of valves for so-called "high end" audio amplification. There are doubtless aescetic and other supporting factors for this, but there is a strongly and widely held view that valve amplifiers simply sound.. preferable. (Audiofile electronics is a field where passions run high verging on religious, preclusing the use of terms such as "better"). The reasons why this is so are complex (for example being due to circuit topology, the transfer function of a valve compared to a transistor, and etc) and are heavily debated, nevertheless the effect is genuine, and is discussed at length in

Main article: valve sound

In comparison with modern, primarily transistor amplifers, valve amplifiers tend to be rather low power, depending on the power tube used), and in particular and often low efficiency The "classical" valve amplifier uses the Directly Heated Single Ended Triode topology (DH-SET), a topology that uses teh gain device in class A. The typical valve using this topology in (rare) current commercial production is the 300B, typically yielding ~ 5 watts. It should be noted however that the simplicity of the DH-SET circuit lends itself to hobbyist construction, so an unknown but perhaps majority of DH-SETs in use today are unique constructions, albeit usually variations of a small number of basic designs. Many hobbyist constructors of audiofile amplifiers are (and are proud to consider themselves) extremists, and this is especially so for DH-SET constructors. A substantial minority of such constructors take minimalism and component selection to extremes, and many so called "flea powered" amplifiers in the 2 watt class are constructed, using tube types that became obsolete pre war, arguing that the minimalist designs have sonic benefits. However such low power output pushes complete replay system design problems firmly onto the louspeaker, requiring very high efficiencies, typically 10dB better than modern mainstream audio loudspeakers achieve, often horn speakers. A separate religious debate rages about the merits and demerits of different speaker technologies, but it is perhaps fair to say that whatever merits extremely low power DH-SET amplifiers may have are partly paid for by problems facing the loudspeaker. A minority of home constructed DH-SETs use extreme tubes to yield up to 25 watts (or beyond) in class A, although the engineering considerations to achieve this are (notably constructing suitably massive coupling transformers while maintaining the desired wide bandwidth) as daunting. Class A amplifers are inherently very inefficient, so power supply and thermal considerations are also problementic for high power designs (which can be solved, but at a price, not purely financial.) During the 1960's and 70's in particular (sometimes referred to as the "golden age" of valve amplifiers, (the height of thier development prior to the introduction of the transistor), the majority of commercial amplifiers adopted derivatives of the class B, push pull, negative feedback topology pioneered by Williamson, this yielding greater power and measured linearity despite using dramatically smaller (and cheaper) transformers. 12-20 watts were obtainable depending on the power tubes used (often EL84, KT66, EL34 or KT88), with high damping factors, and this facilitated the widespread introduction of relatively cheap to produce mutliway box speakers, and the "hi-fi" industry was born. Signal amplifiers using tubes are capable of very high frequency response ranges - up to RF. Indeed many of the vavle types used in SET (Single Ended Triode) amplifiers are in fact designed to operate in the megahertz range in radio transmitters. In practice however tube amplifier designs typically "couple" stages either capacitively or using transformers and these devices do limit the bandwidth at both high and low frequencies. Nevertheless audiofile power amplifiers have substantively flat frequency response accross and beyond the audio band, typically power amps having -3dB points order < 10 hz, > 65 khz. This contrasts with some transistor amplifiers that may go out far beyond 100 khz. Some specialist valve preamplifiers amplifiers (e.g. microphone amplifiers) may be essentially flat to beyond 100 kHz, and remain excellent and amplifiers of chocie (still widely used in studio's). However, the majority of comercial audio preamplifiers made during the "golden age" have complex filter circuits for equalisation and tone adjustment. Today many consider that these devices are fit only for scrap, having both appalling sonics (see valve sound) and also appalling measured performance, notably frequency response and phase linearity. However there are always exceptions, and a small number of excellent commercial designs remain on the market to this day, from e.g. Audio Research and others. Yet the role of "preamplifier" is increasingly tied to teh minority of audiofiles still using vinyl, all "modern" sources beling line level and requiring only switching, buffering and volume control.

[edit] Output transformers

Do all valve amps need an o/p trans or is there some trick to directly connect an 8 ohm speaker say.?--Light current 18:14, 19 March 2006 (UTC)

If all valve amps need an o/p trans, then this will cause a major limitation on the BW and prevent the application of large amounts of NFB due to the nasty phase characteristics of transformers. --Light current 22:57, 30 March 2006 (UTC)

Try a Google search (or the search engine of your choice) for "OTL amplifier". --Reid 64.171.68.130 18:58, 18 October 2006 (UTC)

Valve amps generally do not apply large amounts of NFB, for that exact reason. Surprisingly, scaling down the NFB is not entirely negative. Note, though, that it is quite possible to achieve wide bandwidth (e.g. 10Hz-100KHz), but rather expensive. It also depends on the plate impedance of the output valve.

There are many OTL (output-transformerless) amplifiers out there. You'll probably want to search for "circlotron", which is generally the best OTL topology. If you're looking to build one, you'll probably still want to consider an output transformer, though, since it does a nice job of avoiding 50-3500Vdc across your speaker terminal if one of the valves die.

Designing a transformer for e.g. 20 ohm to 8 ohm conversion is a lot easier to do, with good results, than the same for e.g. 6000 ohm to 8 ohm... A bifilar winding with primaries in series and secondaries in paralell will give you 32 ohm to 8 ohm, for example, with pretty near-perfect results.

Zuiram 05:28, 3 November 2006 (UTC)

[edit] Audible differences

It seems rather strange that the previous vociferous utterances of the audiophile community have not yet been crystallised into a coherent view of what the audible differences are between valve and transistor amplifiers. Is this because they have difficulty in describing these subtle differences or because in fact there are no differences at all?--Light current 03:18, 21 March 2006 (UTC)

There is indeed a difference in sound. The problem is explaining this in words. We don't have many words to describe the characteristics of sounds, we have to use words like 'creamy' and 'crunchy' to describe tube harmonic distortion, which are words to describe texture. Does sound have texture? The 'texture' of sound can only be experienced by you, so you'll have to take the test yourself and see if there is a difference. Otherwise, you have to take everyone's word for it that tube amps sound much 'warmer' and 'creamier' than solid-states. Believe me, for the most part, they do, whatever that means.

Put it in the article! See if it can stand!--Light current 02:09, 25 March 2006 (UTC)

The typical characterization of the difference between a good neutral-sounding valve amp and a good neutral-sounding solid state (transistor) amp is that the valve amp is more organic, warm and smooth, with particularly good reproduction of the human voice and the recording venue's atmosphere. As the others stated, you'll just have to listen for yourself. Human synaesthesia is not uniform between individuals, so the words used to describe it will not mean the same to everyone, at least not until you have your own experience from which to form your own description.

That said, there has not yet crystallized a consensus on whether "valve sound" refers to the sound of good neutral-sounding valve amps, or to the "romantic" highly-colored valve amps. There is a major difference between those two approaches. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Accuracy in recording studios

Dont all recording studios now use opamp and transistor gear for the very reason that valves cause much more distortion?--Light current 17:32, 7 April 2006 (UTC)

I'm sure there are a handful with all-tube fanatics. I'm certain that many of them use tube preamps or tube guitar amps because of their perceived value. If the singer thinks tube mic preamps sound better, you record with one. — Omegatron 18:47, 7 April 2006 (UTC)

I really dont know. I would think today's recording engineerrs decide on which kit to use.Im not, of course, talking about the bands own gear- that could be anything.

Im talking about the stuff the band dont bring with them! This will be chosen from the kit available in the studio. Most modern studios probable now use transistor kit. Therefore....blah blah.

Also I think any effects like 'warmness' (distortion) could be added at the mixing stage, but I dont know if thats how it happens. We need a real recording engineer to tell us how its done.

--Light current 19:08, 7 April 2006 (UTC)

This depends on what kind of recording studio you're talking about.

The good studios usually have a wide selection of equipment, and all commercially viable studios allow the artists a great deal of say over what goes.

But the selection of studios with valve equipment is dropping. I think this is mainly because the current artists aren't very quality-conscious (ref. modern <6dB dynamic range vs original 12-24dB), and because there are few manufacturers of valve studio equipment left.

When the Norwegian band Midnight Choir wanted to record their most recent album (Waiting for the Bricks to Fall), they had to go to Eastern Europe to find a studio that had the all-valve recording-mixing-mastering chain they were looking for. Of course, there are studios in the west that offer this, but they cost a fortune. (I think Sterling Sound Studios (G'n'R, etc.) has this kind of gear, for instance.) That album incidentally clearly demonstrates the more "classic" valve sound, in that the atmosphere, emotion, clarity and presence is outstanding, while the sound can not by any means be considered "neutral". One of the most enjoyable recordings I own, though. I just don't want my own stereo to add to or subtract from what they've already done.

As for "adding warmness", I haven't heard anyone succeed at that yet. You can, however, add a lot of second harmonic distortion (usually by rectifying the sound with germanium diodes, attenuating the rectified sound, and mixing it back in, or doing the digital equivalent). That will yield what is commonly referred to as a "phat" sound, which may be mistaken for warmth if you don't have grounds for comparison, ref. my earlier comments on synaesthesia. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Supposed reasons for valve sound

Quote: "In fact, the harmonics produced by a non-linear device depend on the topology and symmetry of the amplifier; not the type of device used. An amplifier with a symmetric (odd symmetry) transfer function, like a solid state push-pull op-amp, produces only odd harmonics. An amplifier with an asymmetric transfer function, like a class A valve amplifier, produces both even and odd harmonics.[1][2] As valves are often run in class A, and semiconductor amplifiers are often push-pull, the types of distortion are incorrectly associated with the devices instead of the topology.

In order to produce only even harmonics, the device needs a transfer function with even symmetry. A simple example is a solid state full-wave rectifier. Note that the fundamental, which is an odd-numbered harmonic, would not be reproduced at all. (The lowest frequency produced by a full-wave rectifier is double the original; or the second harmonic.) The production of only even harmonics is obviously not desirable in audio reproduction systems, though it is used in guitar distortion.

In audio reproduction systems, the types of harmonics produced should be irrelevant, since proper amplifier design can reduce all harmonics to inaudibility, and they should never see overload conditions. It is, of course, possible that the greater amount of distortion in class A valve amplifiers is the actual reason for the perceptually "improved" sound, even if it is degradation from an engineering standpoint." End Quote

The harmonics produced by a non-linear device are dependent on the device used and not just the topology. The transfer function for a transistor and valve will be different, surely this is patently obvious. The quote that valves are often run in class A and semiconductor amps are push-pull is innacurate - push-pull AB is one of the, if not the, most common valve guitar amp output stage. I tend to agree with the stance on audio reproduction (Im a guitarist not an audiophile) but signal transients from analog input sources such as the magnetic pickups of an electric guitar or a microphone will cause significant distortion http://www.milbert.com/tstxt.htm . Shame the people that contribute to Wikipedia dont actually have to know anything...

Thats right. Even you could contribute- as you have! Please sign your posts tho' by typing 4 tildes ~~~~--Light current 13:46, 23 April 2006 (UTC)

So-called "audiophile" valve amps are usually single-ended triode or class A1 (no grid current) triode. "Audiophile" solid-state amps usually have more power, and therefore tend to use a lower conduction angle to avoid having to dissipate excessive heat. There are, however, a number of single-ended solid-state amps (e.g. Son of Zen (DIY), F1-F3 (First Watt), Aleph (Pass Labs)) and class A solid-state amps (e.g. Sugden) out there.

The choice of active device is clearly relevant, and is independant of the choice of conduction angle. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Canadian English

Tended to use the term "Tube" -- Older tubes were sold by several brands under the trademark "Radiotron" (Marconi, GE, RCA) Rogers used the company name "rogers radio tubes" and I have at least one example where this was molded into the bottom of the base.

cmacd 12:35, 12 May 2006 (UTC)

[edit] Topologies and distortion

THe article says that types of distortion are more dependent on stage topology (configuration) than on the type of device (solid state or vacuum tube technology). 8-?

Would anyone like to justify this statement quoting distortion figures for common base, common emmitter, emitter follower and common cathode, common grid, cathode follower etc before I remove this claim? 8-|--Light current 22:31, 1 June 2006 (UTC)

I had no hand in writing this article, just a few minor link tweaks. However, I have "The Cool Sound of Tubes" in front of me and would like to browse the article to see if this statement can be supported (I am a subscriber to IEEE Spectrum). Gerry Ashton 22:45, 1 June 2006 (UTC)

OK Im eager to see if there are any legit claims. I think the question of distortion in any particular stage is going to be governed almost exclusively by the amount of local NFB applied. BTW I removed the non working link to that article "The Cool Sound of Tubes". 8-|--Light current 22:58, 1 June 2006 (UTC)

NFB is not all that relevant here. What you're looking for is the open-loop harmonic spectrum, which diverges significantly between triodes, tetrodes, pentodes, JFETs, MOSFETs and BJTs. While NFB is, in theory, perfect, in practice, applying excessive amounts of NFB ends up reducing the amplitude of less offensive harmonics at the expense of shifting them to a more offensive set.

Remember that the NFB has to be applied somewhere, and that somewhere is generally the input stage. In theory, again, that should correct things. However, in practice, the input stage is not linear itself, meaning that the correction is non-linear. Some of the papers describing this problem are old enough that you can't even find them online, so it's been known (and often ignored) for some time.

Most valve designers use a moderate-to-low amount of NFB, particularly because gain is much harder to come by in a valve circuit than in a transistor circuit. I've seen transistor audio circuits with 80dB of feedback and 40dB of closed-loop gain, while most valve circuits would be hard pressed to get to just 30dB of feedback. This also figures in the overall sonics.

Zuiram 05:28, 3 November 2006 (UTC)

Must have removed it from another article. Just had a quick read of that article. It doesnt have many hard facts, but it could be quoted from becasue, as you may know, WP is more interested in verifiability than truth!--Light current 23:33, 1 June 2006 (UTC)

I noticed your removal of "The Cool Sound of Tubes" link. Since that is one of my favorite Spectrum articles, I went to the IEEE web site and found where then had moved the article to. I then reinserted the link with the updated URL. BTW, I am quite sure that circuit topology can have a strong affect on the amount and kind of distortion that can occur, and strong negative feedback, either on a single stage or across several stages, can make the type of device seem irrelevant when tested with non-clipping sine wave inputs. The trick is trying to find a reliable reference that (a) will back this up at all, and (b) discuss what happens when playing real music rather than test tones. Gerry Ashton 00:01, 2 June 2006 (UTC)

Yes I agree! Over to you! 8-)--Light current 00:15, 2 June 2006 (UTC)

That raises another interesting point: clipping recovery. At any realistic listening volume, with typically not-so-efficient (<100dB/1W/1m) loudspeakers, both valve and solid-state amps clip regularly, but low NFB improves subjective clipping behaviour (I can dig up the link if you need it), and IIRC, valves recover from clipping a lot faster.

Also note that slew rate limiting can induce a clipping of sorts as well, and you'd be amazed at the HF stuff you end up finding inside the amp if you put a scope on it. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Transfer characteristics of active devices

Perhaps Im being naive here, but I always thought that all active devices had non linear transfer characteristics: some square law, some exponential. Are there any that are truly linear (without NFB) 8-?--Light current 23:22, 1 June 2006 (UTC)

Define linear. Since all active devices, when operated for gain, convert voltage to current, there has to be some sort of input/output transfer function.

The most linear operation you can get, is with VFETs or triodes operated with significant source/cathode degeneration. While that constitutes NFB, it is not global NFB. The resulting I/V transfer function can be extremely linear. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Plan to replace Supposed reasons for valve sound section

I am concerned about the Supposed reasons for valve sound section because it concentrates, at the beginning, on incorrect beliefs about why valve amps sound the way they do. I think it is more important to state valid reasons for why valve amps sound as they do. Eventually, we might address misconceptions, but I think we should find documented sources of those misconceptions.

Also, I feel the extended discussion of even-order distortion and odd-order distortion is not relevant. Although the discussion is partially correct (circuits with perfectly symmetrical transfer characteristics do not have even-order distortion) a peer-reviewed source (see my sandbox) claims that in practical audio amplifiers, the main difference in distortion is that valve amps tend to have lower-order distortion while semiconductor distortion has relatively more high-order distortion.

Mostly correct. Valve amps tend to have a monotonically falling harmonic spectrum which is monotonically proportional to signal level, whereas solid state amps tend to have a non-monotonic harmonic spectrum which is discontinously proportional to signal level. Zuiram 05:28, 3 November 2006 (UTC)

Therefore, I have created a section, Reasons for valve sound, in my sandbox. I don't have much hands-on experience with audio, and hardly any with valves, so I'd appreciate feedback from some of you who might be more knowledgeable before I make the change. Gerry Ashton 04:44, 2 June 2006 (UTC)

Even tho I dont agree with all (any?) of the stuff in the article you quote (cool sound of tubes), it is an independent source from a respectable journal and thus could be quoted in our article. I dont think that article would have been peer reviewed - but so what? It is verifiable and does not have to be true.8-(

However there are also 2 other refs already in the section and these views should be retained also. It would also be nice if pictures of the distortion spectra were refered to illustrating the diff betweeen semiconductor and tube dist.

It is best to write the section in a 'reported speech' style (eg. it is said that ...) rather than to assert 'facts' I feel. Basically every statement or assertion should be able to be referenced from a book, journal, paper etc. Personal views even based on ones own research/intuition are against WP policy. Hope you find this expo useful! 8-|--Light current 07:41, 2 June 2006 (UTC)

Ihave reread the article in question and actually found the diagrams. Now it appears to make more sense and appears to be well written material. Also I would have thought that an article of this nature would need to be peer reviewed.--Light current 19:04, 2 June 2006 (UTC)

To check on Light current's concern about peer review, I went to the IEEE web site and followed a chain of links from the Spectrum page to the information for authors page ([4]). This page states that IEEE publications are peer reviewed. I am not able to find any printed information in the 1998 issue about whether Spectrum was peer reviewed at that time, but I am a subscriber and never noticed any notice in the magazine about beginning peer review.

I'll think about switching to the reported speech style, although that seems stilted to me. I'd appreciate elaboration on what parts Light current disagrees with. I did take care to only report views contained in the article I cited, except for this statement:

Also, since valves are large and expensive, there is incentive to keep the open-loop gain of valve amplifiers low. In contrast, the cheapest and easiest way to build a solid state amplifier is to use an integrated circuit, which has extremely high open loop gain; there is no choice but to use massive amounts of negative feedback to reduce the gain to a practical level.

I consider that statement common knowledge, at least among electrical engineers.

When dealing with audio poweramps, which is where "valve sound" has any meaning, I'm not at all sure the assertion that valves are large and expensive have any real meaning. With the exception of transmitter valves, most valves have glass envelopes that are cooled by natural air convection. The solid-state devices of equivalent power, with equivalent conduction angle (operating class), are forced to use heat sinks to dissipate this excess energy.

Some valves (e.g. 6C45P, 6C33C) are perfectly happy having their carbon plates glowing a dull red from the heat, corresponding to temperatures in excess of 800 degrees Celsius, meaning they don't need much surface area to avoid overheating.

Solid-state devices generally do not handle temperatures in excess of 150 degrees Celsius, and to get any useful power handling out of them, you usually have to keep the temperature in the 50-75 degrees Celsius range. This requires a significant surface area.

Also, since the heatsinks are almost universally exposed in high-power non-pro designs, you effectively need to limit them to 55 degrees Celsius so people won't get burned when touching them. Valves also have the useful feature of glowing when they're hot (except when they're cooling down after use), so you know not to touch them.

While output transformers can be fairly expensive, a 50W quadfilar output transformer wired for 8 ohm to 2x64 ohm will not cost more than a heatsink that can service an equivalent (50W class A) solid-state amplifier.

Zuiram 05:28, 3 November 2006 (UTC)

Barbour's article contains distortion spectrum for 6 amplifiers and a transformer. I could scan some of them as fair use; any opinions on how many I can take as fair use? Unfortunately, the circuits are voltage amplifiers, not final power amps. I understand that the chief difference in tubes vs. transistors are thought to occur in the final stage. BTW, I have a 1959 RCA Receving Tube Manual in case there is anything from there that ought to be posted. Gerry Ashton 15:31, 2 June 2006 (UTC)

OK Gerry, i think the best course of action now would be for you to replace the sect in question with your version and let other editors see it/edit it some more. Please bear in mind that this can be a controversial subject and may attract a lot of 'interest'! I think the spectrum diagrams would each be worth a thousand words if you are sure they are fair use! 8-)--Light current 15:57, 2 June 2006 (UTC)

Eric Barbour is one of the contributors to WikiPedia. Perhaps he can be pursauded to release the diagrams himself.

cmacd 17:27, 2 June 2006 (UTC)

Ah well I dont know whether that would ceate a policy violation or not WP:NOR. The copyright now would be with the publishers IEEE now anyway. 8-|--Light current 17:55, 2 June 2006 (UTC)

That section was originally "Reasons for valve sound", and contained a bunch of myths about harmonic content, which are everywhere on the net. I tried to make it more accurate. I'd make some images of waveforms and spectra if desired.

Your sandbox looks good, though it says some of the same things as my section, and doesn't back up some of its other statements.

Putting up images you created does not violate policy. The copyright is not necessarily with the publisher, either. — Omegatron 18:32, 2 June 2006 (UTC)

Yes but 'O' you seem to miss my point which was that Eric Barbour having sold this article to IEEE spectrum probably does not now own the copyright to these images (or text for that matter)--Light current 19:00, 2 June 2006 (UTC)

Whoa. This article has become pretty cluttered since then. It's got a lot of redundancy.

Also, I don't see any reason why any of these sections should be replaced by the sandbox section. Just merge the sandbox into the article where appropriate, and clean up redundant parts. — Omegatron 18:35, 2 June 2006 (UTC)

I would be facinated to see supporting references for the information about harmonics in the exsiting section. I would also be interesed to know which parts of my version are perceived as not backed up, so I can clarify how it is backed up, or remove it. I have read the IEEE copyright agreement for its authors, and the IEEE does hold copyright, but it licenses back some rights to the author. Also, the IEEE does not pay authors. I also see that is considerable redundancy. Fixing that would require a major rewrite. I'll think about the redundancy issue.

I have created a new page, User talk:Gerry Ashton/collaborate where anyone who cares to do so can mark up my proposed replacement section, so their comments will be close to the text they are commenting on. Gerry Ashton 19:22, 2 June 2006 (UTC)

Thanks Gerry for clearing up those issues! BTW, when I said replace the section, I of course meant merge it with your own additions 8-)--Light current 19:24, 2 June 2006 (UTC)

[edit] Are odd harmonics 'musical'?

...or unmusical. That is: are they desirable or undesirable in an amp? Why 8-?--Light current 19:07, 2 June 2006 (UTC)

1. All harmonics are bad in sound reproduction systems. You want as low distortion as possible
2. Are some harmonics more musical than others? Well, that depends. Define "musical". — Omegatron 20:03, 2 June 2006 (UTC)

C'mon 'O'. We've had this discussion before. Can't remember what talk page it was on now. Common wisdom is that even harms sound OK whereas odd harms sound bad. Both of course are distortions that are not present in the original signal. Im innocently asking the question about odd harms becuase I dont know the answer. Musical means harmonious 8-|--Light current 23:09, 2 June 2006 (UTC)

Actually it was on this very talk page that we discussed harmonics and their musicality! How convenient! 8-)--Light current 23:23, 2 June 2006 (UTC)

I was just going to point that out. #Harmonic_series :-)

All harmonics are harmonious, aren't they? Which sound better to you? Shall I post some samples? Is there a scientific way to determine whether something sounds better or not? I've heard this notion many times before, and I'm skeptical as to whether it has any validity. Maybe it does, but I haven't seen any convincing explanation of why. — Omegatron 00:24, 3 June 2006 (UTC)

As I pointed out earlier here, there have been scientific studies regarding this. 2nd and 3rd are generally innocous. Higher order is detrimental, odd more so than even. A weighting factor is provided, and while I cannot remember it exactly, I do remember that the term was raised to the power of (N/4), where N is the order of the harmonic. Zuiram 05:28, 3 November 2006 (UTC)

Well as I said, this is the accepted wisdom. Im not convinced myself yet. However, I did find a web page earlier today that claimed to show the difference with sound samples containing even harmonics then odd harmonics. They did sound different, but I suspected some trickery or other messing with the sounds apart from harmonic additions. Ill try to find the page again and post it here. I would like to hear your samples. 8-)--Light current 00:42, 3 June 2006 (UTC)

They certainly sound different, but which is "more musical"? Which is better? I suspect it's purely subjective.

Ok, I'll upload something. Let me figure out how to post FLAC files, first.

How about this? Image:Harmonic distortion examples.ogg — Omegatron 01:11, 3 June 2006 (UTC)

OK thanks for that 'O'. Took me a while to find a codec for the .ogg files. Anyway, the tones:

• first sounds pure (bit like a bass guitar with the tone turned down)
• second sounds like an organ with a slightly breathy tone playing in multiple octaves - quite nice
• third again sounds like an organ but not as pleasant as no 2 to my ears!

I would say the second is pref to the third. The first sounds perfectly ok to me being a bass player 8-)(I mean thats how it should sound -right?) --Light current 03:48, 3 June 2006 (UTC)

A bass would have all of those harmonics.  :-) — Omegatron 03:58, 3 June 2006 (UTC)

My bass guitar dont sound anything like those tones (only a bit like the pure tone). Each instrument will have different amounts of each harmonic but those tones had a lot of higher harms for a string bass! 8-|--Light current 04:13, 3 June 2006 (UTC)

Could you make some recordings? We don't seem to have any of bass guitar. — Omegatron 14:45, 3 June 2006 (UTC)

Maybe, if I get some time. There are so many options here that I think we need to say what we want!. What do you think would be suitable:

• single notes,
• over what pitch range
• which strings (EADG) see bass guitar (BTW which bass would you like- I got both shown on this page!)
• what length should each recorded sample be?
• does it need to be enveloped or do you want the attack phase as well
• any other requirements
• I dont think I can make .ogg files. Whats the best alternative format?

Also I'll probably need to 'DI' into minidisc recorder then copy it into the computer and convert the file using Cool Edit before uploading. THis of course will give the raw sound without any cabinet effects. I think thatll be ok.

8-| --Light current 16:00, 3 June 2006 (UTC)

Any and all of the above.  :-) Whatever you have the time and energy to record is welcome. See Bassoon#Audio_examples, for instance. I don't see any bass guitar samples at all.

You have to use ogg format, but it's easy. For Cool Edit, unzip this file into C:\Program Files\Cooledit and then save as ogg. Otherwise, you can download dBPowerAmp music converter and the ogg codec and convert the file by right-clicking on it.

And if you do decide to upload stuff, put it on Commons, not here. — Omegatron 18:31, 3 June 2006 (UTC)

Actually, i may be able to record directly into the computer using Cool edit or some other package. 8-) any advice on how to do this will be welcomw. 8-|--Light current 18:52, 3 June 2006 (UTC)

Yes, that's what I meant. Record into Cool Edit and then save as an .ogg file using the above filter. — Omegatron 23:21, 3 June 2006 (UTC)

Keep in mind that the level of harmonics is also relevant. You want to stay at or below 1%, since even valve amps tend to do so at sensible listening levels. Zuiram 05:28, 3 November 2006 (UTC)

[edit] Facinating reference

I found a very interesting reference:

Russell Hamm, "Tubes Versus Transistors - Is There An Audible Difference?", Journal of the Audio Engineering Society, May 1973.

It can be found at [5]

It will take a while to digest this. Gerry Ashton 01:10, 3 June 2006 (UTC)

Good reference. This should definitely be in the article. — Omegatron 15:12, 3 June 2006 (UTC)

It already is! 8-) [6]. Just a clearer version here--Light current 16:04, 3 June 2006 (UTC)

I know; I just updated it. It's been there forever. I mean the information needs to be in the article. — Omegatron 02:06, 4 June 2006 (UTC)

Ahh! yes 8-)--Light current 02:30, 4 June 2006 (UTC)

This site seems to have some articles about valve sound from a legitimate perspective, too. — Omegatron 04:17, 4 June 2006 (UTC)

Yeah looks like a sensible fellow whose stuff can be referenced. I think maybe we need less exposition and more refs? 8-)--Light current 05:38, 4 June 2006 (UTC)

[edit] Links to milbert.com

Three of the links in the article, in the External Links section, do not work for me:

• PDF Tubes vs. Transistors in Electric Guitar Amps
• Tubes vs. Transistors: Feature Comparison
• Why Tubes?

Does everyone have trouble with these links? Gerry Ashton 00:29, 4 June 2006 (UTC)

Yeah. Maybe Milberts server is down!--Light current 01:49, 4 June 2006 (UTC)

[edit] Audible Differences

I question the article's claim under "Audible Differences" that "it appears that no results from scientifically conducted listening tests are available to confirm or deny the audiophile claims". I think these tests have been done and show that no detectable differences exist when the valve amplifier's distortion is low. For high distortion valve amps the difference is detectable, but only in the same sense as distortion is detectable. Without evidence I suppose this is just hearsay, but it is my recollection. Nowater57

Unfortunatley, we cant rely on peoples recollections, but if you can find a ref. then we can put it in--Light current 13:15, 5 June 2006 (UTC)

I also suspect these tests have been done many times. The aforementioned article (from 1973) says "Previous attempts to measure this difference have always assumed linear operation of the test amplifier. This conventional method of frequency response, distortion, and noise measurement has shown that no significant difference results." — Omegatron 13:30, 5 June 2006 (UTC)

Well of course we can reference the published Hamm article (but probably not the unpublished ones) But there doesnt seem to be hard evidence of controlled tests here. We must look elsewhere--Light current 14:17, 5 June 2006 (UTC)

[edit] Most Guitarists cant tell tube amps from SS

Read conclusion in this IEEE article from 1981 [7]--Light current 15:04, 5 June 2006 (UTC)

I searched on the IEEE web site and found the information needed to cite the article:

W. Bussey and R. Haigler (1981). "Tubes versus transistors in electric guitar amplifiers". IEEE International Conference on Acoustics, Speech, and Signal Processing, Volume 6 p. 800–803. Also note that the summary is available at the IEEE website but the text is not, unless you subscribe to their electronic library service.Gerry Ashton 22:43, 5 June 2006 (UTC)

Well thats OK cos the text is available at [8] 8-)--Light current 00:32, 6 June 2006 (UTC)

[edit] Psychoacoustics

Good paper on ear 'self distortion' etc.--Light current 15:24, 5 June 2006 (UTC)

Shoot! forgot to include the link! Gotta find it again now! 8-(--Light current 00:44, 6 June 2006 (UTC)

[edit] Class A push-pull amplifier

Is there such a thing as a Class A push-pull amplifier, as mentioned in the article? —Bromskloss 20:25, 23 July 2006 (UTC)

It indicates here [9] that there is! 8-)--Light current 16:18, 24 July 2006 (UTC)

There is a tremendous amount of popular confusion on this subject, including the "Harmonic Content and Distortion" section of this page, which needs to be corrected. The author of that section is confusing "Class A" with "single-ended", which is very common (in no small part due to a compendium of inaccuracies and myth called The Tube Amp Book, by Aspen Pittman, which is tragically regarded as authoritative by a lot of people with no other background in electronics). The oppposite of "push-pull" is "single-ended". Either of these topologies can be class A, AB, B, or C, which describes how the gain devices (tubes or transistors) are biased (bias is sort of like the idle speed on a car engine). Operating class has nothing inherently to do with the circuit topology. It happens that in audio, all single-ended amps are also Class A, because they would sound horrible if they weren't, but push-pull amps can also be Class A if their gain devices are biased such that all devices conduct the signal at all times (i.e., they idle "hot" and no device ever falls into "cutoff"). Comparing "push-pull" with "class A" is a classic "apples & oranges" error. Class A also has nothing to do with whether the output is cathode-biased or fixed-biased, another common misconception promulgated by the book cited above. Amplifier operating classes are described well in the Wiki aticle on Electronic Amplifiers. --Reid (I should register...) 64.171.68.130 18:50, 18 October 2006 (UTC)

In practice, nearly all solid state amplifiers are push-pull, and they are almost invariably not class A, though many claim to be. Sugden has true class A solid-state amplifiers that are push-pull. Many valve amplifiers are push pull, and a large number of these are also class A.

The reason is quite simple: "true" class A effectively means that the idle current must be at least equal to the maximum signal current. This means tons of heat, which must be dissipated somehow. A valve can stand several hundred degrees celsius, while a transistor will need to be kept to a few tens of degrees above room temperature. That, in turn, means that it needs a lot of (expensive) heat sinking.

Simply put, the cost usually outweighs the benefit in solid-state amplifiers, so they are usually biased for "class A" operation up to a few watts (rarely more than the first 25W), which is really class AB. But you can find, or build, "true" class A solid-state amplifiers (360 degree conduction angle). The money will often be better spent elsewhere, though.

Preamplifiers are almost invariably true class A, whether single-ended or push-pull, since the relatively small power levels involved (5Vrms into a 75ohm load is about 300mW, and that's pretty much a worst case) don't usually necessitate any excessive heatsinking. Zuiram 05:28, 3 November 2006 (UTC)