Hifi Gurus/Engineers/Reviewers

[Arkless Electronics]

Sounds like a bit of a hot potato this one, the main problem with Hi Fi is everyone has their own opinion, i know what you're getting at Rob for trade members to act as like a "bullshit" filter and advise where clever marketing has been employed by the manufacturer, however i also understand where Jez is coming from, as soon as he gives his opinion there will be folks out there saying he has an ulterior motive or some such nonsense because he's in the trade.

As this is an enthusiasts forum, i would have thought the insight given by any member is worth taking into account.

Precisely. Also the OP mentions tweaks etc and I'm apparently barred by site ethos from saying what I really think about the majority of tweaks.....

[Marco]

Not barred; as long as you say what you think once, and then let others who disagree do what they like afterwards, without being endlessly 'spanked' like silly schoolboys!

Marco.

[Reffc]

Having seen the stick engineers often get on here for suggesting that some beloved tweaks are a waste of time because they simply can't do 'what it says on the tin', I doubt you'll be getting many takers.

This.

Plus, please be mindful that most of us still active in the hifi design and construction business would find it unpalatable offering criticism of others' work...the right minded amongst us simply wouldn't take part in offering such opinions on a public forum. There are many ways to skin a cat and there are many companies and individuals doing things their own way.

Now where there was a blatant example of marketing trying to deceive by lies or by claiming that magical nymphs power their box of tricks, it would be only too fair to point out that nymphs don't exist (sorry, block the eyes of any children reading, but neither does Santa) and to perhaps offer the truth behind a claim rather than to rubbish a statement outright. It is dangerous ice to tread on though. A little re-thinking might help. Perhaps something like a section to share technical articles or personal thoughts on design might be more appropriate?

[Firebottle]

I'll take up the cudgel (oops, sorry – thread) on this one.

Having an enquiring mind in matters of a technical nature I'm always keen to try to understand what causes changes to the sound we listen to.
One aspect that has puzzled me is the differences caused by valve rolling, after all the valve is usually being replaced by one of the same type/designation, though usually a different make.

I'll try to keep this simple so everyone can understand my thoughts.

Firstly some basics, no components are perfect, if they were there wouldn't be any difference in the sound of X, Y or Z amplifier models.
If only 'a straight wire with gain' was something that could be achieved, sadly not.
Gain in this instance is another word for amplification

The gain of a valve stage is dependant on the conditions it is operating under, primarily what voltage is across the valve.
The problems arise from the fact that it is not just the characteristic that determines the amplification (gm) that is non linear compared to the voltage across the valve, the 'equivalent internal resistance' (my terminology) of the valve, known as ra, is also non linear with respect to the voltage across the valve.

A resistor is a basic building block in all electronic circuitry, perhaps one type approaching 'perfect' being the Z foils, at affordable prices; http://www.hificollective.co.uk/comp...resistors.html

Now combine what may be a near perfect external resistor, the load resistor on the valve anode, with the non linear internal ra and differences can easily arise.
To quote from Keith Snook,
'The complex interdependencies changing internal gains and impedances within a triode amplifier as Va Ia and Vg change dynamically cause all kinds of distortion and colouration ~ Simply isolating one cause of distortion such as the non linearity of the Ia/Vg transfer function cannot fully explain the differences between the sound of similar or even the same type of valves'.

Full article is here: http://www.keith-snook.info/amplifie...cb-graphs.html

There are design techniques that can mitigate most of the non linearity of valve characteristics, used to great effect by the likes of Tube Distinctions (AnthonyTD of this very parish) and Shindo to name but two.

A majority of valve amplifiers may well use supply regulation to good effect but that only goes part way to negating the valve amplification stage non linearity, hence different sounds when valve rolling.

I use various techniques in my own design amplifiers, probably why they sound as good as they do