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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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15th Jun 2018, 2:28 pm | #21 |
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Re: Valve sound?
I'm sure your right GJ and my lack of musical knowledge is showing. I don't really know about harmonic numbers so the comparison was non existent really, apples and oranges. On the other hand the odds and evens theory [in terms of the output distortion itself] does seem to stand up at some level, just not in terms of intervals perhaps
Dave I suspect that thread explains where I got the idea Mosem Dave.. Thanks! Last edited by dave walsh; 15th Jun 2018 at 2:36 pm. |
15th Jun 2018, 2:47 pm | #22 |
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Re: Valve sound?
Valve sound exists, but then your talking about music, which is very subjective. When you factor human's into the equation it becomes more complex. It's probably 10% valve sound 90% headology.
Bob Carver claimed to be able to make any amplifier modelled on any other. HH made transistor guitar amps that took some beating, but most lads who noodle on the guitar are going to go for a Marshall/Vox/Fender, it's what everyone else does or did. Andy.
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15th Jun 2018, 2:56 pm | #23 |
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Re: Valve sound?
I get the impression that early transistor amps could apparently test impressively under single-tone testing- but that using real-world music made for a harsh and fatiguing sound- the effects of intermodulation distortion had been overlooked, hence the expectation nowadays that amps need two-tone testing at high power to reveal any shortcomings in this important aspect of behaviour and have any credibility on the market. That might have explained some of the preference for "good ol' valve sound" originally, and it lingered long after solid-state designers had worked on improving their products to an impressive degree.
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15th Jun 2018, 5:25 pm | #24 |
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Re: Valve sound?
Crossover distortion was the major bugbear of early transistor designs - the delicacy of the available devices encouraged low quiescent currents, the measured value of the distortion was not great and the effect took some time to be recognised for what it was - see L.N. Hulley's extensive review of the Dynaco 120, around 1967 when, although he could hear a difference between this and two decent types of valve amp, he didn't attribute it to distortion. As is now well known, the 120 in standard form has plenty of crossover distortion, especially when cold. Hence my comment earlier that audible differences can be accounted for by measurement once you know what to measure.
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15th Jun 2018, 7:29 pm | #25 |
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Re: Valve sound?
Another factor which complicates our ability to judge how something will sound when all we know is the harmonic spectrum that it generates is that spectrum analysers often don't give phase information. The relative phases of the harmonics can make a dramatic difference to the time domain waveform.
Attached are two pictures showing, in heavy black, two time domain waveforms. I've assembled these by adding up a fundamental (light brown) and its first few odd harmonics - third, fifth, seventh, ninth, eleventh and thirteenth. Some of these harmonics are shown in other colours viz. the third (red), fifth (green) and seventh (blue). In the first picture the phases of all the harmonics are such that when the fundamental crosses the zero axis all the harmonics have the same sign (positive or negative) of slope as the fundamental does. I've chosen the individual harmonic amplitudes so that this generates something approximating to a square wave in the time domain. If I added all the odd harmonics, at the right amplitudes, up to infinity then I would get a perfect square wave. The second picture shows exactly the same harmonics with exactly the same amplitudes. So a spectrum analyser, which commonly displays just a power spectrum and doesn't indicate phases, would show exactly the same harmonic spectrum as for the first picture. But now I've shifted the phases of the third, seventh and eleventh harmonics by 180 degrees, effectively inverting them. You can see that the summed black waveform is now very different from a square wave. To be honest I haven't listened to it, but I don't imagine it would sound the same as the square wave. The moral of the story ? Don't try to make precise predictions about 'sound' if all you've got to go on is the harmonic spectrum. Cheers, GJ
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15th Jun 2018, 8:44 pm | #26 |
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Re: Valve sound?
Back in the late sixties and seventies I used to be a vocalist at large holiday camp. We used Shure microphones and Carlbrough 100watt valve amps.
The sound was clear and crisp, with a little bit of spring reverb is sounded like singing in a large church, and was just about perfect, in my opinion. After many years of service it was decided to upgrade the lighting system and the sound system. A Shure Vocal Master System was installed, this was a fully transistorised mixer amp, 100watt if my memory is correct. The system was very good, even the late Sir Harry Secombe told me it was good, however I never found it had the same clean crisp sound that I had got used to with the old valve amp. Maybe the amps today are better! Cheers John |
15th Jun 2018, 9:47 pm | #27 |
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Re: Valve sound?
When people hear my old radios they often say it's the valves that make them sound so warm and pleasant, in reality it's probabily more to do with the interaction between the speaker and the large wooden cabinet.
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15th Jun 2018, 10:59 pm | #28 | |
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Re: Valve sound?
Quote:
In Roederer's 'Physics and Psychophysics of Music' there's a section on tone fusion - why is it that when presented with a bunch of harmonics of a complex musical tone, we hear one note with timbre and not a bunch of discrete tonal events. To unpick this one has to get into cochlear dynamics and the ciritical band idea - I'm going to go on too much of a tangent, so I'll just say that your idea has been used as a demo to find out how tone fusion works, by synthesising odd waveforms from non-harmonic components whose phase structure changes over time. Even though these false harmonics are resolved separately on the basilar membrane, we perceive a kind of changing, rolling timbre rather like a guitar 'flanger' or 'chorus' effect - and theories exist as to how the brain picks up this waveform information, even though generally a spectral hearing model (with very little phase information) describes the large majority of hearing phenomena. Oh - and upthread you mentioned the discordant 7th harmonic. I wonder if you know that most pianos aim to have the hammer hit the string about 1/7 of the way along; if you excite the string near a displacement node for a given mode, that mode will be somewhat suppressed in the overall harmonic line spectrum. |
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15th Jun 2018, 11:11 pm | #29 |
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Re: Valve sound?
The so called fuzzbox has, since its inception always been a solid state unit. Now, there are stand alone valve distortion units but these are used to emulate or enhance the sound of a valve amplifier or to get a 'valvey' sound when using a SS amp - nothing to do with fuzz. The difference between a SS fuzzbox and a valve distortion unit is considerable. The fuzzbox tends to have a very raw, ragged, even harsh sound that works best on single notes and has a tendency to sound dreadful on chords. It was used a lot for guitar solos in the 60s. Conversely, the valve distortion unit sounds sweeter and works well on single notes and chords.
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16th Jun 2018, 12:02 am | #30 | |
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Re: Valve sound?
Quote:
Given the nonlinearities of the less perfect elements in the audio chain, particularly speakers, I can imagine that the two waveforms I've shown might look different even in the frequency domain after they've been transduced. But of course they're not realistic waveforms for a hi-fi amp. Third harmonic at 33% and 5th at 20% would be scandalously bad. Amplitudes a hundred times lower are more typical. It's recognised though that people can hear 1-2% distortion quite reliably. So I still find it surprising that they might not be able to tell my two waveforms apart. Cheers, GJ
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16th Jun 2018, 12:15 am | #31 |
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Re: Valve sound?
Amplifier specification generally base specifications on pure sinewaves into resistive loads but I have found most people listen to music over speakers. This in mind I would say there is no empirical evidence to support the theory that a 'valve sound' does not exist. My experience is high quality SS amplifiers can sound a bit clinical whilst my Beam Echo (Mullard 5-20) does seem to be more fun with my Castle transmission lines with less bass control and more dynamics.
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16th Jun 2018, 1:06 am | #32 |
Octode
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Re: Valve sound?
There is bound to be a difference in sound due to the two modes of operation. In one you are controlling electrons in a vacuum and in the other electrons (and holes) in a solid medium. The other factor to consider is that most SS designs rely on controlling higher currents and like a large crowd of people running fast, it takes a little longer to make them change direction. This we call the transition time and is the reason, for example, that spikes are generated from transformer fed bridge rectifiers when they are supplying large currents. Having used SS amplifiers for 35 years, I tried a valve amplifier and never looked back. With 45 watts per channel and only 8 watts needed to fill the room, the old argument about over drive distortion levels never enters the equation. At the end of the day, the type of sound one prefers should be respected, some like SS and some like valve. Each and everyone of us has different hearing and it may be that one person likes one type of amplifier over another. Guitar valve amplifiers are something totally different, they generally do not employ feedback to give wider bandwidth with lowest distortion. They tend to be often over driven as their soft limiting makes the amplifier give more dynamics to the guitar. It has often been said that a guitar valve amplifier forms part of the guitar itself. The downside for me and many others using valve equipment is the unreliability of modern valve manufacture with fireworks often appearing in the output stages. The problems I have had are mainly screen grid leakage which I can only assume to be poor mica's and electrodes becoming disconnected internally by poor welding of the interconnects. But even with all of these problems, I don't think I will be going back to SS amplification, hollow state suits me but fully understand while others think the reverse and I respect that.
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16th Jun 2018, 8:51 am | #33 |
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Re: Valve sound?
The difference between valve and transistor hifi is very visible. Valves get mounted on the outside and they light up! Couldn't be more obvious.
But there are other differences less visible. Valve amplifier design evolved and matured in the era before transistors. Valves were very expensive, incomes were low, and they were used sparingly. Feedback, if any was also used sparingly. The gain per stage had to be kept high in order to economise on valves, and this meant a roll-off and phase shift creeping in at the upper end of the audible frequency range. This phase shift and that of the output transformer (needed to arbitrate the difference between the impedance of a speaker voice coil and the impedance valve anodes worked best into) set a limit on how much feedback could be employed before stability problems loomed. Consequently, the characteristic non-linearities of the valves is seen in the performance of the complete amplifier. This is OK because the characteristics of most valves are not only inoffensive, many people like them. The mildly-shaped distortion, the tendency to high-frequency roll-off and a soft curve into saturation give what has become known as the valve sound. When transistors came along, they too were expensive, but not as expensive as early valves had been. Still, their numbers were kept low, and designers stuck to the styles of circuit design evolved for valves. The results were awful. Thermal runaway was a new problem, countermeasures were more sticking plasters than cures. The characteristic curves of the devices did not sound good in the minimalist designs used. Transistors amplifiers got a bad reputation, and they deserved it. The reputation blamed the transistors and not the circuit designs they were put into. As they say, first impressions count, and reputations once formed, stick. Later transistor designs became more sympathetic to the transistor's characteristics, stage gains were no longer pushed to the limit as more devices could be used, and this also created new freedoms in the design which took care of thermal runaway. All looked rosy in the garden. These amplifiers looked good when you measured them, but some people said they didn't sound good. It turned out that there were some performance issues that didn't show up in the frequency response plot and total harmonic distortion figure which graced all the magazine reviews and manufacturer's blurb. Eventually, the cause was found and ways of designing it out evolved. Inevitably, the reputation from this era has also stuck. Nowadays, it is possible to design a very good amplifier indeed, using transistors. It has no sound of its own, you get whatever sound got recorded/broadcast. Some people find this 'sterile', But if so, 'sterile' is what is on the record. Do they want to hear it as it is, or would they rather have it changed to suit their preference? A simple valve design can do this, but a simple transistor design can't. We can do things to valve amplifier designs to get around their imperfections if we aren't so tied to minimising valve count. We can engineer out the 'valve sound' and produce a genuinely neutral amplifier. Some high class amps had gone in this direction before their evolution stopped. No-one called them 'sterile', though. Maybe this was psychological, because they had those hot glass things sticking up out of them and everyone knew valves must produce 'valve sound'. Just for a lark, I made some amplifiers, designed for very wide frequency range, very low distortion and very fast slew rate. I tried them out on a number of people and no-one could tell them apart. The valved one, because of its circuit design, exhibited a hard, fast, clipping characteristic like its semiconductor siblings. I knew which I was listening to, and I thought I could hear differences, but then I heard them the wrong way round when I found I'd made a mistake and wasn't listening to the amplifier I thought I was. If there were differences, they were lost in the noise of uncertainty and suggestibility. So, a lot of the 'valve sound' and 'transistor sound' stuff really lies in the circuit design. With basic, minimalist circuit design transistors sound bad and valves produce effects that some people actively prefer and some will pay big money for. With advanced circuit design, the valve and transistor sounds disappear. Your choice then gets limited to transistors because I don't think there were many valve amps built this way. If there is some boutique amp on sale, the price will likely be out of reach. To quote from Rowan & Martin's Laugh-In: "If it feels good, do it!" Listening to music is for enjoyment. David
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16th Jun 2018, 8:57 am | #34 | |
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Re: Valve sound?
Quote:
Cheers, GJ
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16th Jun 2018, 11:22 am | #35 |
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Re: Valve sound?
Gordon King it was indeed, thanks for that. I can't even remember what I have written in a post so have to look it up before I can answer it.
My introduction to valve amps was when I started work in '54, we sold Leak, Quad and the like , mono of course but I have not heard anything since to beat the quality of those especially with really good speakers, Lowther particularly impressed me. But of course its subjective as has been well documented. Peter |
16th Jun 2018, 12:03 pm | #36 |
Octode
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Re: Valve sound?
Reasonable figures for an old clunker but catastrophic by solid state standards! 0.5 ohms output impedance at LF (e.g. where it really matters) is a bit on the high side, assuming everything else is optimal. Probably didn't sound too bad through your (sealed box) NS-1000s though...
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16th Jun 2018, 12:20 pm | #37 | |
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Re: Valve sound?
Quote:
Cheers, GJ
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16th Jun 2018, 12:24 pm | #38 |
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Re: Valve sound?
I can't remember ever listening [well watching] an old valve TV that sounded unpleasant - but there again, all necessarily featured decent 'enclosures'.
Whereas ............. many modern flat screens sound truly awful - hence the preponderance of add-on 'sound bars' etc. ?
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16th Jun 2018, 12:32 pm | #39 |
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Re: Valve sound?
0.5 ohms output impedance means DF=16, which is high enough for most purposes.
If parameter X needs to be no greater than Y for good audio results, and a valve amp achieves 0.3Y while an SS amp can do 0.01Y then this does not mean that the SS amp is 30 times better as a domestic audio reproducer although it might be 30 times better as a piece of laboratory signal processing equipment. |
16th Jun 2018, 12:42 pm | #40 |
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Re: Valve sound?
On a point of detail, the output impedance at 50Hz was 0.47ohms and the properly matched load impedance would have been 11ohms, so the nominal DF would be more than 23.
Cheers, GJ
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