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Old 16th Jun 2018, 1:03 pm   #41
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Default Re: Valve sound?

Quote:
Originally Posted by Peter.N. View Post
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.
I think that what you've illustrated is that mankind has been able to make amplifiers which are about as good as they ever need to be for quite some time. This doesn't mean, of course, that all amplifiers made since then have been to that standard.

After some false starts and dead ends, solid state amplifiers can now be made to a good standard, too. That also means that not all recent solid state stuff is any good. If you take care to pick good examples, you now have a free choice of what type of active device to use.

Over the time period you refer to, recordings have changed a lot. I find many of the multi-miked and mixed to hell products sound muddled compared to the clarity that was achieved on the best of the fifties recordings.

I too like Lowthers. Their single driver approach avoids some of the difficulties inherent in multi-driver speakers. Multi-driver speakers have advantages, but a lot of effort needs to be spent to prevent losing some of the benefits the single driver had.

We live at an interesting time. We can pick the best bits from the new stuff and from the old stuff. There are good things from both periods and bargains can be spotted. I can afford things now that were out of reach back in the day.

To anyone who wants to live exclusively in the past, I have one word to say:


"Dentistry"


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Old 16th Jun 2018, 6:23 pm   #42
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Default Re: Valve sound?

I am not an engineer, but can offer a few personal observations as a lifelong hifi lover, hobbyist and listener now in my 60s.

I remember the sound of my parents' big Grundig and thought this was the glow of memory till I bought a valve radio from an old secondhand shop about 20 years ago, and was amazed to hear the same pleasant sound. I don't know the model numbers of either, but a few years ago I restored a Bush VHF70 with the help of this forum, and that provides the 'warm' valve sound when needed.

But about 15 years ago, on a whim, I bought an unrestored Verdik Quality Ten and was amazed to clarity and beauty I had never heard before. It hummed and clearly needed work, but those two EL84s sounded wonderful to me, and made my CDs sound wonderful too. The floodgates opened and I spent the next decade buying and learning restore all the classic valve amplifiers I could afford. I learned that not all sound the same, even with the same circuit, e.g. Heathkit MA12s do not sound as good to me as the Dynaco SCA35, or the Verdik though both have similar sized UL transformers. Given the similar circuits, I attribute that to the particular sound of particular output transformers.

Different valves sound different too: EL34, 6L6, 5881, 7591, etc.

Confusingly, to a non-engineer, even the same valve in the same amplifier can sound different under different operating conditions. I remember when I was replacing the 117V power transformer in my Dynaco ST70 with a 240V one taken from an organ, that it sounded amazingly good with higher than correct voltages on the anodes. I brought the voltages down to the correct ones listed in the Dynaco circuit, but with some regret.

There are other factors open to dispute. Some prize old NOS valves, and I possess some nice Mullard EL34s, but my ST70 sounds fine to me with some cheap modern ones from China.

One area where I really can hear the difference is in phono stages. Valve ones, and mine are just builds of the Maplin Newton design, sound to me much better than SS equivalents, such as good quality NAD or Trio amplifiers from the same era.

One last thing. Tinnitus. I used to attend dances with loud SS sound systems which really worsened my tinnitus. I find that listening to valve amplification quite loudly at home does not.

There is a lot to be said for valves, IMO. And that is why my moniker is Qualityten.

David
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Old 16th Jun 2018, 6:44 pm   #43
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Default Re: Valve sound?

Post 38 Trachionist said he never listened to a bad sounding valve tv, I agree that most were good, however I do remember one Murphy TV with a flip up lid/speaker/ on/off switch that was pretty terrible, don’t remember model number but we in the workshop thought it was a very bad design particularly from Murphy. It’s one redeeming feature was the whole cabinet came off in one go making it very easy to service.
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Old 16th Jun 2018, 7:23 pm   #44
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Default Re: Valve sound?

I find I'm a lot less critical of sound when there is an accompanying moving picture. Also TV set sound will have been remembered as judged against the expectations of TV sound.

95% psycho, 5% acoustics..... psychoacoustics!

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Old 16th Jun 2018, 7:40 pm   #45
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Default Re: Valve sound?

I wanted to like Lowthers - I appreciated their approach and the hand craftsmanship involved, but after six months of living with a pair I still found them shrill and unnatural.
It's not only affirmation bias which drives these preferences!
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Old 16th Jun 2018, 11:21 pm   #46
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Default Re: Valve sound?

The grass is always greener...

I'm surprised at the rate some people on hifi fora keep changing equipment. They must be under a curse not unlike the flying Dutchman. Damned to never find peace.

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Old 22nd Jun 2018, 8:34 am   #47
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Default Re: Valve sound?

How do people go on when their front-end & output stage are a hybrid combo, usually (though not always) a valve pre-amp, solid state power amp? I've heard arguments about 'best of both worlds'.

Surely the best of both worlds would be, have a valve hi-fi systems, and a solid state one(?)

Source material plays a huge part to the overal sound, along with components, room acoustics, possibly room temperature (in extremes?), mood & hearing abilites (frequency range).

Lots of unknown variables at play, if it looks right & sounds right

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Old 22nd Jun 2018, 2:01 pm   #48
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Default Re: Valve sound?

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Surely the best of both worlds would be, have a valve hi-fi systems, and a solid state one(?)
I think it is done to at least some extent, though I have little interest in going there, but maybe the ideal for that would be digital with really good sampling rate and reproduction, and switch between programming for different sound.

Personally I prefer the simplicity of the original though. A lot easier to sort when it becomes problematic a few years down the line. Even when a valve (or even transistor) is obsolete and unobtainable similar types can be used and the skill and references required are more easily achieved.
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Old 22nd Jun 2018, 9:41 pm   #49
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Default Re: Valve sound?

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Originally Posted by mark2collection View Post
How do people go on when their front-end & output stage are a hybrid combo, usually (though not always) a valve pre-amp, solid state power amp? I've heard arguments about 'best of both worlds'.
I've a guitar amp which works like this. Mine (Marshall Valvestate) does not have a great reputation / image as far as I can tell, but having owned a few 'classic' all-valve designs (70s Marshall Master Volume 100W, 60s JMI AC30) I'd say the current one is far more flexible (clean, mild crunch, full-on fuzz - all at any volume you fancy, including quiet) and a whole lot more portable It was also free with a simple (even for me) fault, which endeared it to me from the outset.
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Old 23rd Jun 2018, 8:48 am   #50
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Default Re: Valve sound?

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Originally Posted by John10b View Post
Post 38 Trachionist said he never listened to a bad sounding valve tv, I agree that most were good, however I do remember one Murphy TV with a flip up lid/speaker/ on/off switch that was pretty terrible, don’t remember model number but we in the workshop thought it was a very bad design particularly from Murphy. It’s one redeeming feature was the whole cabinet came off in one go making it very easy to service.
Cheers
John
Wow! I'm not familiar with the set to which you refer - but [as you have alluded] quite 'innovative' and very remiss on the part of the traditionally staid and usually bullet-proof Murphy offerings?
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Old 23rd Jun 2018, 12:55 pm   #51
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Default Re: Valve sound?

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Originally Posted by Radio Wrangler View Post

So, a lot of the 'valve sound' and 'transistor sound' stuff really lies in the circuit design.

David
My brother who is more of an audio amplifier enthusiast than I am, subscribes to exactly this theory and I think there is good logic in it.

Valve amplifiers, by necessity (unless high Z speakers are used) need an output transformer.

After transistors came along there was an economy drive to eliminate coupling and output transformers from transistor amplifier designs. After all they were big , heavy and expensive items. Profit margins are much better without them. And the square wave response (amplitude & phase distortion) were better in lab tests without the transformer, so multiple reasons to get rid of the transformers. This is probably what created what audiophiles call "transistor sound".


After that, to get a "valve sound" back again, with transistors, is to simply use a similar sized iron cored output transformer (to what a valve amp of similar power would use).

An output transformer acts as a bandpass filter, limits both the LF and HF response of the amplifier and alters the clipping properties of the output stage to a softer form of clipping, with lower high frequency range harmonics than you get with the harsh clipping and idealized square wave response from a transformer-less (typically transistor) amplifier.

I think its likely that the perceived difference between valve and transistor amplifiers is more to do with the transformer & circuit design than the "electron control devices" after all both the transistors (silicon) and valves in most cases are capable of frequency responses from DC into the radio frequency spectrum, well beyond audio.

(There is one exception, perhaps, as pointed out in the textbook Electronic Devices & Circuits by Millman and Halkias, McGraw Hill 1967, Sec 18-5 page 553: It is possible to set up a Pentode amplifier's operating conditions for zero second harmonic distortion, this is not possible with a transistor)

My brother built a push pull transformer coupled amp with transformers and AD149 output transistors and subjectively most of his audiophile friends agreed it sounded exactly like a valve amplifier. Of course, from the laboratory testing perspective, the transformer would have added phase and amplitude distortion.

Motorola also produced an interesting paper (I think it was 1970's or '80's) on the many benefits of using output transformers in transistor power amplifiers. If I find it, I'll post it.

Last edited by Argus25; 23rd Jun 2018 at 1:02 pm. Reason: typo
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Old 23rd Jun 2018, 2:14 pm   #52
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Default Re: Valve sound?

The yardsticks used to measure amplifier performance are the issue. Low output impedance into a resistive load with a 1kHz sinewave does not mean it will behave as if it had this output impedance when presenting a music signal to the varying inductive and capacitive load of a speaker. Maybe the industry should pay more attention to this rather than focus on uranium treated interconnects.
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Old 23rd Jun 2018, 3:38 pm   #53
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Well, "a piece of wire with gain" has long since been done. The Knights found the Holy Grail. Only it turned out to be pretty boring when compared to the pictures that have been drawn of it, the descriptions that have been written about it and the cheap plastic imitation grails sold to curably rich tourists in gift shops .....

I dare say if you built a multi-stage amplifier with lots of matched pairs of pentodes in parallel push-pull directly driving a specially-made speaker with a high-impedance voice coil and copious use of negative feedback, and a transistor amplifier with minimal use of feedback and a transformer coupling the loudspeaker to the output stage, people in a blind trial would tend to think the latter amplifier had the "characteristic valve sound" and the former was "solid-state clinical".

You can't expect everyone to like the same things anyway. It would be a truly boring world if we did.
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Old 23rd Jun 2018, 8:30 pm   #54
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Default Re: Valve sound?

The original 'transistor sound' was probably caused by crossover distortion, not lack of OPT distortion.

Softer clipping is not primarily a transformer issue but a feedback issue, and secondarily an active device issue.

Someone, I forget who, made a good transistor amp sound indistinguishable from a good valve amp by doing two things:
1. add some LF and HF rolloff
2. add a series resistor to increase output impedance
In both cases the changes were small, as the amps were good to start with and with or without these changes they were within spec for what most people would regard as hi-fi. Given that no speakers are perfect, it is not possible to say which amp actually gave the flattest audible frequency response - just that both were good enough although slightly different.
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Old 23rd Jun 2018, 10:25 pm   #55
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Default Re: Valve sound?

It all interacts. The phase shifting in an output transformer puts a limitation on the amount of feedback which can be deployed in conventional valve amplifier circuits.

The same thing affects transformer coupled transistor circuits.

The basic distortion characteristic of a valve doesn't sound too objectionable and many people feel it 'improves' the music. The distortion is fairly mild and the onset of clipping is gradual.

The basic distortion characteristic of a transistor is not really that much worse on its own than that of a valve. But the circuits transistors find themselves in are usually class-B with a fairly hard crossover non-linearity which sounds very bad. The solution to this has been to try to get the biassing as close to optimum as can be arranged, and then to deploy large amounts of feedback to scale down the remaining no-linearity. This feedback and the high gain that the feedback is around, creates sharp-cornered abrupt clipping that sounds bad.

If you choose valve amplification, you can get away with fairly simple circuits, but a lot of dmand gets placed on having good valves and good transformers if you want to keep the distortion low

If you choose transistor amplification, you really are pushed into having a high gain amp with a lot of feedback around it. The clipping issue can be fixed by having a ridiculously powerful amp by valve standards just so you can be sure the thing stays out of clipping.

If you are a musician and curved clipping is wanted as part of your performance, valve circuits do this naturally. Try it with a plain transistor amp and it sounds awful. To have any chance you need a ludicrously powerful amplifier so it never clips, driven by a smooth clipping simulator.

You can drive 8 ohm speakers with direct-coupled valve amplification - no output transformer. It takes a stupidly large number of parallelled bottles, doubled up for a totem-pole push-pull circuit. I know, I was stupid enough to build one! The amount of heater power in a vast array of line output valves is enough to make it pointless.

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Old 23rd Jun 2018, 10:30 pm   #56
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You can drive 8 ohm speakers with direct-coupled valve amplification - no output transformer. It takes a stupidly large number of parallelled bottles, doubled up for a totem-pole push-pull circuit. I know, I was stupid enough to build one! The amount of heater power in a vast array of line output valves is enough to make it pointless.
So the £64 000 question .....

What did it sound like?
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Old 23rd Jun 2018, 10:46 pm   #57
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Default Re: Valve sound?

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Originally Posted by G8HQP Dave View Post

The original 'transistor sound' was probably caused by crossover distortion, not lack of OPT distortion.

Someone, I forget who, made a good transistor amp sound indistinguishable from a good valve amp by doing two things:
1. add some LF and HF rolloff
2. add a series resistor to increase output impedance.
I don't know about the first remark, most of the transistor amps I have tested are definitely biased out of cross over distortion even for very low volume signals unless they are faulty or out of adjustment. So at normal listening levels I cannot see how that could be too significant, unless the amp was faulty or incorrectly biased. On the other hand with the wide dynamic range of music as a signal, peaks get clipped sometimes even at moderate listening levels.

Though recently I was surprised to see the significant amount of cross over distortion produced by the LM358 Op amp, but that is unusual for most OP amps too. But it is true that the crossover distortion seen in incorrectly biased valve push pull amps is much more gradual and has much lower frequency harmonics than the transistors case, unless passed through an output transformer where they soften up, a little.

The LF & HF roll off and increase in output impedance (which reduces the damping in the speaker circuit) is exactly what the output transformer does. So that makes perfect sense that it would emulate the valve amp.

On the idea of high impedance speakers, one of the better TV audio systems I have ever heard or seen, was from a 1960's vintage Philips TV set, that had two high Z (probably 600R good quality stiff paper cone speakers) no output transformer and a totem pole output stage. The audio was wonderful. But it seems that this idea was not all that popular with other makers. I think there was also an impressive radiogram called the Carnegie Hall that used a similar system, but I'm not 100% sure as I have not seen the schematic.

Also as David points out the presence of a transformer and its phase shift properties, limits the amount of possible negative feedback that can be applied before instability occurs. On the other hand so does RC coupling between consecutive stages, and enough feedback will then turn your amplifier into a phase shift oscillator. Probably the better compromise is the lowest distortion possible per stage and then the minimum amount of global negative feedback applied after that.

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Old 23rd Jun 2018, 10:56 pm   #58
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Default Re: Valve sound?

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What did it sound like?
Well, um just like the transistor one.

The point of doing it was to compare it with an equally over-engineered pair of transistor based amplifiers (Bipolar and FET output devices) I tried them in blind tests with numerous people where neither I nor anyone else operating things knew what was selected. The outcomes were sufficiently scattered to convince me no-one could reliably tell them apart.

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Old 23rd Jun 2018, 11:02 pm   #59
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Default Re: Valve sound?

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LM358 crossover distortion
The LM358 isn't a good choice for audio applications for that very reason. You can reduce the distortion a lot with careful circuit design, but there isn't much point given that better alternatives are available at little or no extra cost.
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Old 23rd Jun 2018, 11:19 pm   #60
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Default Re: Valve sound?

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Originally Posted by G8HQP Dave View Post
The original 'transistor sound' was probably caused by crossover distortion, not lack of OPT distortion.
And that crossover distortion in many early transistor amplifiers was the result of the inherent asymmetry of the widely used Lin quasi-complementary output stage, and not just a question of (mal)adjustment of the crossover process itself.

A good explanation was provided by Bailey in the preamble to his 1968 amplifier design in Wireless World 1968 May, p.94ff. I have attached the first couple of pages of that article.

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In part, that was a retroactive explanation for his choice of transformer drive for his earlier 1966 amplifier design, as well as an explanation for his choosing a fully-complementary output stage for the design at interest, suitable PNP devices then having become available.

The inherent problem with the Lin circuit was known to some of the amplifier makers and designers in the second half of the 1960s. Some practiced avoidance. As well as transformer drive (e.g. Bailey, Rogers) class A operation was an option (e.g. Sugden, Linsley Hood). Piling on the NFB, as mentioned by Bailey, was another apparent approach, brute force perhaps (I think Leak did it that way). Others worked on improving the Lin circuit to make it symmetrical. Along this vector were the Quad output triples in 1967, followed by the Shaw power diode in 1969 (realized in the Welbrook amplifier) and also in 1969, the Baxandall diode. The last-mentioned I think became the norm for quasi-complementary outputs. Whilst the fully complementary output stage was thought to have been the “answer”, there were those, notably Vereker of Naim, who questioned its symmetry, and so preferred the Baxandall circuit.

The germanium vs. silicon issue may have been part of this. In the article on his 1966 design (WW 1966 November p.542ff), which offered a choice of germanium or silicon output devices, Bailey noted the germanium option offered lower distortion than silicon.

I suspect that the term “transistor sound” was coined in the 1960s to describe some of the early transistor amplifiers. And that the “valve sound” term came later in somewhat of an antidotal manner. Actually, I have a recollection that “transistor sound” was first used to describe the execrable sound produced by early (and many later) transistor portable radio receivers.

One could say that very good amplifiers, whether valve or transistor, don’t have a “sound” and are essentially indistinguishable. However, in the descent from the “very good” plateau, valve amplifiers tend to move along a vector that would be described as “valve sound”, whereas solid-state amplifiers move along a vector that would be described as “transistor” sound.

So to return to the original question, it is probably fair to say that “valve sound” does exist, and in a generalized way represents the sound typically produced by valve amplifiers when they depart from the “very good” level. But it is not an immutable property of valve amplifiers; a competent designer whose objective was a true hi-fi amplifier would make sure that it was not there.

Be that as it may, it is clear that no amount rationality and good science will supervene the pseudo-science that is invoked in support of individual beliefs and preferences, not just in the audio field, but generally. “Flat earthing” is alive and well in the “information age”. Or, in colloquial terms, bovine 3-methylindole baffles brains.


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