On Mon, 14 Jun 2004 08:43:02 +0100, Jim Lesurf
wrote:

In article , Keith G
wrote:

"Jim Lesurf" wrote in message
...


The performance of an amplifier comes from the way all the components
work in conjunction. Just replacing one item with a 'better' one might
simply make the performance worse...


Indeed, 'upset the balance', as it were. In which case one would need to
reverse the changes or move onto different components, which I guess is
pretty much how valve amplifier designs are finalised anyway.

There is a state in the process of devolpment and design which I tend to
call 'lost in space'. :-)

This is where you have a number of variables (choice of component types,
choice of values, slight topology changes, etc) and want to 'optimise' a
design. Since they all tend to interact, if you just try changing one thing
or another you can end up 'wandering about' in terms of the state of the
unit. With luck (and time!) you can end up in a place which seems OK.
However you may then have no real idea *why*. Nor know that a better result
might be nearby, but you never wandered past it...

I must admit that a lot of what I've read about the process of people
trying 'different' components to see what they does sound a bit like the
above to me.

Part of the appeal of valve kit to some people is that it can be
'tweaked' in a comparatively easy way, making the amplifier a more
significant contributor to the overall sound characteristics of a
'hi-fi' system. Not that everybody thinks that is necessarily a good
thing - I've been so pleased with the sound I get using my own kit amp,
I've never been tempted to fiddle with it......

My worries about the above a

1) The 'lost in space' problem. Might be a 'better' arrangement that could
have been cheaper and easier if you'd known.

2) People then not knowing that the resulting amp is unstable or marginal,
or has a reduced life or safety margin. (I am particularly worried about
this when a design is developed for kit use as the original development may
then not have covered properly the effects of normal component variations.
I recall WW kit designs being called 'Worked Wunce' rather than 'Wireless
World' by some professionals. :-) )

For the above reasons my own inclination is to treat the system as a whole
and do relevant measurements as well as listen. However I am unsure how
many DIY or kit builders do this.

Slainte,

Jim

This problem is particularly to be found in the "high end", where
there is simply not enough time and money to develop a design
properly, which generally takes a large number of models to establish
- as you imply - criteria for tolerance sensitivity, stability etc.
The result is that every unit sold is essentially an under-designed,
under-tested prototype, which really should never have left the
premises.

A properly-engineered design simply never gets the chance to happen in
this market, whereas further down the food chain, not only can it
happen, but it absolutely MUST happen, or heads start rolling.

d
Pearce Consulting
http://www.pearce.uk.com