Good morning, Jim, and indeed a fine sunny one. I'll see if I can address your
comments.
I can see that component changes might be more noticable with such a valve amp
than with many SS amp designs.
I don't build SS, but I would guess that you are right about the factors
involved - low or zero global feedback, transformers, variability within valves
being greater than between chips and probably also the larger voltage
differences within circuits that substitutions make, compared to regulated SS
voltage rails.
However for the same reason I might personally tend to prefer a SS design
precisely because it might give less scope for component variations having an
audible effect.
This is interesting, because I'm sure many people like valve amps because they
CAN make audible changes by swapping componants. This gives them an interactive
role in their audio passion, which they appreciate since it gets them more
involved. I'm sure I don't need to point out that 'interactive' is one of the
buzz popular appeal subjects of recent years.
with your detailed construction notes which prove that substituting
componants has no effect on the sound.
How could a set of notes 'prove' this?
Exactly, I was being ironic. I thought my ironies were more transparent!
I'd be interested to know how you verify or test your own perceptions in
this area
Being 'lost in space' is part of the creative process e.g. it would be second
in a simple four stage model consisting of Orientation, Incubation, Inspiration
and Verification, and could well be quite anarchic in nature. Inspiration would
signify that some of the variables looked very promising, so this would then
become the 'breadboard' or prototype. Verification could take different forms
depending on the requirements. In a DIY amp, it may be sufficient that it
sounds good to the builder, with the obvious proviso that it should be safe and
stable. For a production model clearly more verification and safety testing
would be required, but I'm strictly talking DIY here. The experienced amateur
builder would, however, not be happy with 'sounds good'. He/she would want to
know as much as possible WHY a componant change made a difference, and further
than that how it could be repeated in different circumstances. One way to do
this would be to build an infinite number of prototypes and make careful notes.
This is exactly what most inventors did - e.g. the Wright brothers with their
many prototype 'planes. At a later stage, hopefully, would come theory and
equations (as with aviation models) but the DIY builder may largely work by
trial and error. Not to be dismissed out of hand - it has its merits. If I need
a set of scope measurements and distortion tests for a circuit I go down the
road to my designer friend who designs commercial products and has a proper
bench setup. I have a scope but using it is still on the 'to do' list of
projects. So my verification is partly subjective and partly intelligent trial
and error and careful notes of results achieved, voltages, componants, etc,
tests which I do with a multimeter and analyse in Excel, using equations
derived from books like Morgan Jones, Menno van der Veen etc and data on
Duncanamps (valve data, power supplies) and other audio sites. I also have a
valve tester to test the valves I use to see how they perform, so I at least
know that.
In my experience it is one thing to have an impression that a change has had
an effect. It is something else to test this over a period of time in a way
that can reliably rule out uncontrolled variables
This is true of so many things in life - I'm sure we could think of numerous
examples. I wouldn't even try to claim I'd eliminated all uncontrolled
variables, though one does try to use as much methodology as one can.
=== Andy Evans ===
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