Valve amps - do measurements tell it all?

[cloth-ears]

What is it with you Richard ? why don't you just take up wrestling it would keep you fit as well, far better than typing
Seriously though what do you consider an adequate damping factor I cant recall the figures at present but I have heard atmasphere valve otls that could drive a diesel locomotive
nevermind stiff paper cones (being a esl fan cant think why you would want to).
Paul
ps Bob I could not find the specs on a 606 to find a comparative amp, so no munching yet
Paul

Quad 606

Output, 2 X 140W 8 Ohm (both channels driven)

Maximum distortion (up to clipping point), 0.01

Output stability, Unconditionally stable into any load

Damping factor, 250

Hum and Noise, 105db

[SteveTheShadow]

Of course measurements matter with valve amps, just as much as they do with transistors.
Take second harmonic for example, too much of that and the thing sounds as if treacle has been poured over everything, such is the cloying sweetness. It can be attractive, but soon becomes wearing.

What you want with a valve amp is a decaying waterfall of harmonics so that the higher orders, fall away rapidly to insignificance. High order odd harmonics in particular, can give a nasty edge to the sound and must be dealt with if your valve amp is going to be any good. Triodes do this best, pentodes need feedback to sort out non linearity and reduce high output impedance so that the output stage interacts properly with a loudspeaker load. ultralinear is a half way house, giving much of the triode's lesser output impedance and sound, without the need for as much feedback as pentodes.

Single ended feed-backless valve amps are good at pulling off this harmonic waterfall trick and are capable of stunning refinement and style. Push pull amplifiers tend to cancel even harmonics and sum odd harmonics so they can be more troublesome to get right, but it is by no means impossible. Some fabulous sounding push pull triode, pentode and ultralinear amps have been manufactured in the past.

With push-pull, you get more power but at the expense of ultimate refinement. However PP will drive real world speakers far more cheaply and effectively than a single ended class A valve amp. To get equivalent power and speaker driving capability to a class A/B PP KT88, with a SE setup would need big transmitter triodes running KV of HT voltage.

For me the small trade off of refinement in favour of power, is worth it, for others SE is the only true way.
Both approaches are equally valid. BUT be very very sure, either topology with poor measured performance will
sound like crap compared to a properly designed and built amplifier.

Your valve amp won't reproduce music properly unless basic engineering principles have been used in its design and construction. After that, voicing it at valve and component level is more to do with experience and art than science, especially if you want your amp to be more than just another "me too" product.

[cloth-ears]

So no issues with preamps and phono stages?

My only issue with valve preamps is that I find them very temperamental. As I have now gone fully digital I only use a passive pre so not a problem.

[Ali Tait]

I've used a WD Pre 3 and before that a Pre 2 for many years with no issues whatsoever.

[The Grand Wazoo]

I've been using the same valve pre-amp for 20 years and the only problems I've had with it were caused by me messing about with it when I should have known better.

[Arkless Electronics]

The entire problem with valve power amps is the output transformer! OK not having "PNP" valves is rather awkward but it can be worked around....

I can design valve pre amps and phono stages with just as low distortion and wide bandwidth as solid state. It's not really an issue. Noise is lower with solid state but this only becomes a major issue if designing an MC phono stage.

OTL valve amps are never really all that successful due to the fact that valves simply aren't a low impedance device. It can work but they have to be "forced" to do that trick.

I have designed and built a power amp using valves for everything except the output devices (no drivers or anything) and it measured 0.005% THD, 1Hz - 500KHz -3dB points and damping factor of a few hundred. It's only the output transformer that prevents figures such as these from valve amps.

With the very best transformers and best topologies it is possible to achieve 0.03% THD (or there abouts), 10Hz - 50KHz and damping factor of about 30 but it is unusual to see figures such as those.

SET's ? simply not hifi. Sorry.

[Oldpinkman]

I'm not going to get drawn on measurements, because in spite of digging out "secrets of vacuum tube amplifiers" again for a brush up, I don't really know my arse from my elbow. Just a few thoughts to keep it warm and bubbling

Valve fans are either attracted by that "warm" , often "rolled off" sound, or by the even order harmonic sweetness - and probably enjoy the electrostatic speaker, relishing the smoothness of vocals, strings and "tonality", whereas those enjoying a bit more rough and tumble, rock fans, and even those wanting a full orchestral effect prefer good solid state when they can get it. Even die-hard valve designers don't major on "slam" or "control".

By way of extending that to professional audio - valves tend to be used in microphone preamps and the like precisely BECAUSE they colour the sound. They are used in guitar amps, where "attack" "pace" etc are not critical, but even though a guitar valve power amp is enough to fight with a PA in small venues , nobody makes a valve PA amp.

[loo]

I only use OTL valve amps apart from lots of Quad II's which I inherited , and with the right output valve selection and a decent circuit design no trickery is involved, they are some of the simplest amplifiers around and the most stable, any of my OTL,s is quite happy powered up and unloaded for hours on end.
Paul

[Marco]

My only issue with valve preamps is that I find them very temperamental.

Then name and shame those "temperamental" valve preamps, I say, because there is no excuse for it - certainly it is not a problem endemic with valves. I've owned a Croft (all valve) preamp now for 8 years, which on average gets used for 5 hours each day, and have not had a single problem with it, nor indeed have I with my TD Copper amp, which gets the same amount of daily use, and which I've owned for 5 years.

Providing that a valve amplifier has been properly designed in the first place, and is used and looked after properly by its owner, it should be just as reliable/non-temperamental as any solid-state amp. Therefore, in those circumstances, the oft-mentioned "temperamental" or 'fussy'/'unreliable nature' of valve amps is a total nonsense and misnomer. Quite simply, if that's what you've experienced, then you haven't owned a decent one!!

As for measurements, again a lot of bollocks is talked about. Within established and relevant parameters, all GOOD valve amplifiers should measure well. Indeed, I've yet to hear ANY amplifier valve or SS measure badly, but sound good! In my experience, the two factors are intrinsically linked. In that respect, my Croft preamp measures flat to at least 100khz, and down to a few hz at the bottom end, and I believe my TD Copper valve power amp behaves in the same way, although Anthony can of course verify this.

Of course, some solid-state amps will measure better in certain areas than a valve amp will (types of distortion), but not in any way I've found that matters to me. As for driving speakers, it's all about correct matching. Find a reasonably efficient pair of speakers, which are a 'valve friendly load' (i.e. that don't exhibit horrible dips in impedance or have overly complicated power-sucking crossovers), of which there are many examples to choose from, and you're fine!

Like Ali says (and Steve also talks much sense here), given what I've heard from truly top-notch valve amps and phono stages, I've yet to find SS ones I could live with in the long term. In comparison, most sound rather anodyne and musically un-involving.

Marco.

[Marco]

Valve fans are either attracted by that "warm" , often "rolled off" sound, or by the even order harmonic sweetness - and probably enjoy the electrostatic speaker, relishing the smoothness of vocals, strings and "tonality", whereas those enjoying a bit more rough and tumble, rock fans, and even those wanting a full orchestral effect prefer good solid state when they can get it. Even die-hard valve designers don't major on "slam" or "control".

Slam??

Hehehehe... I can't wait to see the look on your face when you visit and I play some Rammstein or Tool at full tilt on my system. All I'll say is make sure that you pack a clean pair of incontinence pants!



Marco.