Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

John Phillips wrote:

In article , Trevor Wilson wrote:

"mick" wrote in message
.. .

You can produce two signals with identical THD%.

**Yep.

One will have very audible distortion and the other won't.

**Yep.

It depends on the relative strengths of the harmonics.

**And the TOTAL level of those harmonics. Less than around 0.1% is
inaudible, regardless of the harmonic structure. That is why I cited 0.1%
as being a reasonable indicator of 'high fidelity'.

Out of curiosity I have been looking for tables of "just detectable"
distortion levels versus harmonic number. However I have not found
one yet.

There are some clues as well as the 0.1% figure above (well, maybe
clues if you take magazine reviews with just a small a pinch of
salt). From a Stereophile review of a Cary CAD-300SEI valve/tube amp
(http://www.stereophile.com/amplifica.../index5.html):

"It's a common mistake to consider a single THD figure an indicator of
distortion audibility. The THD+N figures in the previous graph sum all
harmonics and noise for a single figure and ignore which harmonics are
present and in what ratios. As you can demonstrate for yourself with
the second Stereophile Test CD, 0.3% of seventh-harmonic distortion
is more annoying than 10% of second-harmonic distortion. Generally,
lower-order harmonics are less audible, as are even-order harmonics
(second, fourth, sixth). The most benign harmonic distortion is
thus second-harmonic."

This appears to claim 0.3% of seventh is "annoying". The reviewer then
goes on to write (with an editorial comment):

"... Because the distortion is primarily low-order, the 300SEI can
get away with having several-percent THD. [While the distortion will
be audible, it will be relatively musically consonant, which is not
the same thing as being inaudible.Ed.] "

Maybe I will have to write a test CD or two and see what I can hear
under informal test conditions (especially since I do not know my
loudspeakers' distortion spec. figures).

I assume distortion levels are quoted as voltage ratios (even though
what may matter to the ear could be different)?

--
John Phillips

The above post ignores the much more relevant issue of
intermodulation distortion resulting from the transfer curve which the thd is a
measure of.

Harmonics in music are its very essence, so a fraction of a percent more or
less harmonics if they are 2h, 3h, 4h or 5h or 6h makes little difference.
At a concert, each person at a different seat in the audience gets a different
balance of harmonics.
But the music is spoiled if the imd mounts up as a result of excessive thd,
because the imd products are not
harmonius with the musically related tones.
Amps with predominantly 3h thd may possibly make worse music than amps with
mainly 2h
in their thd profile, because the imd caused by 3h is worse than that caused by
2h.
..
But an amp with considerable 7h could be a disaster.

I must say I have not witnessed much 7h in anything I have tested, unless
the level was taken to the brink of clipping, when by that time the the
mix of harmonics has mushroomed, as opposed to am amp working at 1/10
of its maximum power, where the mix of harmonic products is less complex,
and also the imd mix is less complex.

Patrick Turner.

Valve amp (preferably DIY) to drive apair of Wharfedale DiamondII's
 

Ian Molton wrote:
Nick Gorham wrote:

Ian Molton wrote:

If you took a moment of your time to noitice that I had snipped all
the text that didn't relate directly to my reply, you may even get to
read it in the first place.


Thats a matter of opinion...

Ok, You win, you are entirly correct, award yourself a gold star, write
"Yes I am right" on a scrap of paper, and pin it to your forehead.

Well done, do you feel better now ?

--
Nick

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

In article , Rob
wrote:
Jim Lesurf wrote:


IMO entire human perception is shrouded in distortion and I find this
whole debate about 'causal distortion' a red herring.


I would agree that it does seem to be the case that human physiology
means that our hearing system is quite non-linear, and hence does not
always react as we might think. However I don't think it follows from
this that distortion in audio equipment is a 'red herring'. It can
alter the results in an audible way, and hence must matter if we have
an interest in the results.

Well, I think the red herring is the association. Many of the technical
contributors near enough instantly associate 'the distortion of valve
amps' with 'imperfect sound amplification'.

Again, there can be a distinction between "imperfect" and "unsatisfactory"
or "worse". The ouput from pretty much anything can be said to be
"imperfect". However we then may have for form a judgement on what (if
anything) this may mean in a given case/context.


That for me is just not good enough. Think of the amp as a lens - a
valve amp 'bends the light' in a way that allows focus. Some wouldsay
distortion, I'd say focus, and it's the curious sense of space that
valve amps relay plus the 'smoothness'.

Two difficulties here.

One is that as with all analogies the one you are invoking may or may not
be a reliable guide for the point at hand.

The other is that I am not clear if you are talking about rays of lights,
or the image which may be produced.

And anyway, isn't distortion from a valve amp (say 25w) negligible at
decent sound levels (say 5w)?

Afraid I can't say. The problem here is that the above is a generalisation,
like many of the other statements people make in this area. This isn't
simply a matter of the power level. Also involves the details of the
design, the details of the musical waveform, the speaker load, etc, etc.

[snip]
I have learned this by listening, not measuring.


Again, by "learned" here you presumably mean "I have formed this
feeling as it seems consistent with hearing a difference and
preferring one sort of amp".

However would it not also be quite consistent with your experience to
say that you prefer the sound altered in a given way by a valve amp,
so simply miss this when listening to a SS amp? - i.e. it does not
tell you anything about the presence or absence of distortion in a SS
amp beyond saying it does not share the distortion of a valve amp?

More or less, yes. It's just that I'm unhappy with the word 'altered'.

Why? By being unhappy with the word you may be assuming an implication that
need not be drawn in a given case. Changing the overall level is an
'alteration' but it may be for the 'better' or the 'worse' (or neither)
depending entirely upon the context, etc.

Valve amplification (or at least all that I've heard) just gets me
closer to the essence of what I believe music sounds like.

Fair enough.

You would say altered - because the amplified signal deviates from the
original recorded pattern to a greater extent.

I *might* say 'altered'. The problem, though, is that it becomes difficult
to make sense (in scientific/engineering terms) of some of the things
people say as they seem to:

1) Either use terms with no clear definition that can give that means much
to someone who does not share their experience and judgement. (This tells
us that in language terms, the words used were free of information content
as they fail to convey anything in the message.)

2) Use terms with an implied/assumed meaning which contradicts the standard
definitions used by engineers/designers/scientists who work on these areas,
and do not flag up this distinction. (Which then leads to confusion,
argument, and a general lack of progress whilst people argue at cross
purposes.)

Hence I do not know if the term 'altered' is relevant or discriptive for
what you (and other describe). I can suspect this, and suspect possible
forms of 'alteration' may be involved. But it is difficult to move from a
suspicion onto even a hypothesis given the communication problems I have
outlined.

The incredibly frustrating thing for scientists is that my explanation
has all the credibility of say a homeopathy advocate. All I can say
(again) is have a listen - I can't explain it.

I have listened in the past to various valve amplifiers in various systems.
Sometimes I have heard effects which sometimes seemed quite good - for
specific items of music in specific systems/circumstances. However,
overall, my personal preference turns out to be for the types of SS amp I
use, just as it tends to be for CD-A. Hence my personal decision is based
upon both listening experience and various interests/activies in the areas
of design engineering, etc, etc.

I have no complaint about those who prefer valve or vinyl, though. My
interest is in understanding this in terms that illuminate both the
physiology involved, and the designs. Alas, this is difficult for the
reasons I have outlined.

Slainte,

Jim

--
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Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

In article , Patrick Turner
wrote:

[snip]

The efforts of ARC is such that their amps produce astonishly low thd
figures at 2 watts.

You may be correct. However I find it difficult to comment on things like
this as reviews, etc, often fail to do measurements with a variety of
complex loads, etc. Hence I find that I often don't have the data to
comment in detail on the implications which might be drawn from those
values they do give.


I just sold a pair of new SE 35 watt amps which I made with 4 x 6CA7
configured with cathode feedback OPT windings and global NFB to make a
total of about 16 dB, which is a lesser amount of NFB than compared to
1960, and even though its SE, the thd is no more than a normally low thd
PP amp, simply because I have chosen the driver stage carefully enough
so that the 2H of the driver triodes cancels the 2H produced in the
output tubes.

The thd is less than 0.1% at up to 10 watts into any load between 4 and
12 ohms, which means that at 1 watt its down around 0.03%, even though
it is an SE amp.

That is quite good in itself. Does it maintain that into reactive loads, or
in 'intermod' situation where both LF and HF are present?

I'd also be interested to know the (complex) o/p impedance as a function of
frequency and perhaps power level....

[snip]

But an SS amp needs to have 10 times lower thd at the same levels of the
tube amp, say 0.003% because they mainly operate in the middle of the
switching region of the output transistors, and although the thd is low,

I note the "mainly" in your statement. :-)


its spectra isn't too good.. Since there is no OPT to cause the phase
shifts at F extremes, lots of NFB can be applied, and hence the thd and
resulting IMD is supposed to be inaudible.

...and may, indeed, be inaudible. Depends upon the design and the
circumstances. As does your "mainly" qualifier above.

[snip]

Not all SS amps are plain crook, but enough are to give SS a bad name.

Alas - as your own comments about older valve amps indicate - you could
make similar statements about valve amps. :-)

So we come back to one of your main points/implications. That SS or valve,
it depends upon the design and the conditions of use and what individual
people actually prefer. All these vary from one case to another.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

In article , Keith G
wrote:

"Jim Lesurf" wrote

[snip]

Agreed. However we have to also bear in mind that some 'personal
opinions' may read as if they were assumed to be, or presented as,
general statements of 'fact' about the physics, etc, of the real
world. In such cases they may be tested (and perhaps falsified) by
some suitable method and shown 'wrong'.


Let's put this into a different perspective: If some **** *chooses* to
interpret a stated opinion as a fact he is either a fool or up to some
form of mischief....

Agreed. The reader/receiver has a responsibility to make a fair effort to
understand the message. However the writer/source also has a responsibility
to try and ensure the message can be reasonably free from ambiguity or
misleading language. For communication to be possible the source and the
receiver have to co-operate to that extent. This means in part an agreed
'language'.

It also means both parties being alert to the possibility of
misunderstandings, and being willing to try and clarify if they wish
communication to actually take place.



OK, that was all very interesting, if a little tautological, but it
seems to me you are basically saying that someone expressing an opinion
must do so in a way which leaves no margin for error or
misinterpretation.

Not quite. I am quite aware that leaving "*no* margin for error or
misinterpretation" is impossible. :-) (Please see below...)

Fine, but when an opinion is expressed at large to
number of people it is inevitable that it will interpreted differently
by at least some of them.

Tell me about it. I have taught large classes of undergrads, so could
probably do the statistics on that! ;-

My point is that, unless they find it disadvantageous so do to, anyone
with a genuine interest in that opinion will do what they can to reduce
the possibility of misunderstanding, will they not?

(You know, start most of their statements with the words 'Not sure what
you mean....?? )

Indeed. It is a phrase I am sometimes guilty of writing. :-)

So my point is, indeed, as you describe above. That those involved should
be alert for this and make reasonble efforts to sort out misunderstandings
over meanings of words, etc, if they wish to communicate. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
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"Mike Gilmour" wrote



Dunno Patrick I went back to Svetlana's 6550C's again because I lost at
least 50% of the dynamics with the '88's but gained some (psudeo?) 'air',
IMO not worth the trade. Tried KT90's which went far too far in the other
direction :-)


Interesting. I'm running my KiT88 with Svet 6550Cs in and have been for a
while now.

This started out as a temporary measure when I had a KT88 go down leaving me
one can short of a 6-pack, as it were, but since most of the people who get
to hear it have continued in their admiration of the sound (and the cost of
a set of four KT88s being not exactly chump change) I've not got round to
replacing them yet.

Is it your opinion that the 6550s are a better valve generally? - I'd sooner
not spend £150 or more to find out they are, if that's likely to be the
case!!

(I can't say I 'remember' a vastly different sound myself.....!!??)

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Hello Don - I was a bit loose about my use of 'unbeliever' - as you rightly
point out. Have no fear - I'm as cynical as the next man, and I learn a lot
from (and enjoy) your posts and those of Jim, to name but two. No what I meant
was "those who refuse to believe on principal", which I don't think refers to
you or Jim - you're always open to consider ideas.


=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

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I refuse to learn to dislike something musically superb for its trivial
technical imperfections.


I just listened to Rubinstein playing Mozart and Chopin in mono from a live
concert. Before that was Sofronitsky playing Scriabin, same quality. You're
talking to the converted here, mate!

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

In article , John Phillips
wrote:


Out of curiosity I have been looking for tables of "just detectable"
distortion levels versus harmonic number. However I have not found one
yet.

Nor have I. I have found various references and reports of different
experiments, and they don't all agree. However I'd expect that, as in many
cases (particularly with older work) they may have sufferred from other
distortions in the test system.

There are some clues as well as the 0.1% figure above (well, maybe clues
if you take magazine reviews with just a small a pinch of salt). From a
Stereophile review of a Cary CAD-300SEI valve/tube amp
(http://www.stereophile.com/amplifica.../index5.html):

"It's a common mistake to consider a single THD figure an indicator
of distortion audibility. The THD+N figures in the previous graph
sum all harmonics and noise for a single figure and ignore which
harmonics are present and in what ratios. As you can demonstrate for
yourself with the second Stereophile Test CD, 0.3% of
seventh-harmonic distortion is more annoying than 10% of
second-harmonic distortion. Generally, lower-order harmonics are
less audible, as are even-order harmonics (second, fourth, sixth).
The most benign harmonic distortion is thus second-harmonic."

This appears to claim 0.3% of seventh is "annoying". The reviewer then
goes on to write (with an editorial comment):

"... Because the distortion is primarily low-order, the 300SEI can
get away with having several-percent THD. [While the distortion will
be audible, it will be relatively musically consonant, which is not
the same thing as being inaudible.Ed.] "

The difficulty with comments like the above 'stereophile' ones is that they
are almost certainly reliable in some cases, but may well not be in all.
Thus we have to be careful in drawing general conclusions from them.

A particular problem is that THD figures with sinewaves or test waveforms
that are simple harmonic series do not necessarily serve as reliable guides
when the music is more complex. Nor does a single value tell us what noting
how the distortion varies with signal level may indicate. This is
particularly important given the dynamics of music and the complex nature
of speaker loads.

As a result, simple THD values for a sinewave into a resistor are useful,
but limited in terms of the implications we can draw. 20% THD would warn us
that there may be a problem. But figures in the range around or below 1%
have to be treated with caution if we lack any other information.

Maybe I will have to write a test CD or two and see what I can hear
under informal test conditions (especially since I do not know my
loudspeakers' distortion spec. figures).

I assume distortion levels are quoted as voltage ratios (even though
what may matter to the ear could be different)?

The standard seems to be to work out the Pdist/Psig then take the square
root, then x100 to get a percentage. So a signal that produced a single
harmonic at the -40dB (w.r.t the signal) level would be specified as 1%
THD.

Thus they are effectively an rms voltage ratio expressed as a percentage.
This discards any phase or harmonic number info.

Slainte,

Jim

--
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Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

"Nick Gorham" wrote


Stewart Pinkerton wrote:

we

???

Continues to represent a body of opinion? Seeking 'safety in numbers'.
Lonely? Has friends after all?


resent valvies telling us that SS
amps produce 'cold, harsh' sound, when what is *really* happening is
that good SS amps reproduce their inputs faithfully, while valve amps
do not, but *add* artifacts which some people prefer.

Hence the kind of comments which you quite rightly ascribe to us
above. In the real world, there *is* no audible distortion in good
modern amps (SS or valve), they *are* to all intents perfect, and
here's the clincher, they *do* all sound the same.


Fair point, and taken.


I disagree. Although I can't distinguish between the (probably mediocre) ss
amps that I have myself or have come my way, I certainly can with valves and
that is part of the appeal. This continual tub-thumping about *our* (note
the 'we' factor) ss amps are neutral, it's *your* (note the divisive 'you'
factor) valve amps that are coloured/distorted/crap/wotever is getting to be
like the little white spot you used to get when you shut the telly off.

Valve amps are back - they're all over the Net, they're all over the comix,
they are even on the up in this group. I think it's getting time to let King
Canute and his friends float off into the sunset so those of us who like or
are curious about valves can get to discuss them here (a *UK* group) without
getting pushed on to the defensive all the time.

As you know, my doors are/have been open to anyone (within reason) who
wanted to hear valves as they are not (yet) that easy to hear in the shops.
*No-one* has been subjected to anything like a sales pitch and my own
enthusiasm has always been constrained at least until the visitors have
expressed a positive view themselves. No-one has told me that don't like
valves and nearly all have gone out and bought valve equipment of some kind.

I don't believe the comments repeated above are in fact 'fair points' is
because AFAIAC they are only one (loopy) person's opinions and prejudices
and, as such, do nothing to encourage exploration in all things of an audio
nature. Worse, they are trying to affect some form of control over
proceeedings here. I don't give a little f*ck on a stick who
likes/uses/dislikes/doesn't use valves, I do give ALFOAS about people having
the chance to make up their own minds on the subject without being
continually battered about the head by a few self-appointed
experts/moderators in this group....