Output Transformer
I’m not going to touch on output transformer design, am I?
Are you interested?
Designing an output transformer is very difficult,
especially on a new core, or on cores where the designer is unfamiliar with. Theory
is one thing, making a physical unit is a totally different story. You can get
all the calculations correct but it still ends up where you do not want to be
at – talk about Murphy’s Law.
We would aim for 1% deviation from designed value, which is
something that is very hard to achieve if one is not experienced enough where
they would go for 5% or more tolerance since vacuum tubes also has around 5-10%
tolerance.
As we all know, audio spectrum spans from 20Hz to 20kHz that
is 1000x of change! If one is more stringent, they would design from 10Hz to
100kHz for modern high definition audio. It is very difficult to control the
impedance or frequency response change to <0.5dB across that spectrum.
The output transformer, being the soul of a tube amplifier,
will hold the gate towards to how good the amplifier can sound. We cannot
depend on sheer luck to design an output transformer that is flat across the
audio bandwidth. It has to have proper design, taking into consideration all
the learning from previous actualization experience, extensive material
research (core, wires, bobbin, winding techniques and etc), where all starts
align, to obtain the almost perfect response we need.
A lot of DIYers just hear from others (reliable sources or
not!) or just trust what the paper specifications says. Mind you, the world is
full of conman, or cunning marketers to part your hard earned cash for
something unworthy, rather than really earning them with solid engineering
skills and manufacturing for quality.
Output transformer design is an art! Everybody can calculate
but not everybody can build good output transformers, just like everybody can
draw, but not everybody can be an artist! Even if it is having the same
windings ration, identical materials, but the outcome with be day and night of
differences. I’ve seen component or equipment manufacturers that have not
improve since they started. What I got 10 years ago is measured to be the same
now. If it is something good, never mind, but it is something that is lousy…
I’d like to urge the DIYers, don’t just listen, don’t just
plug & play, measure and qualify your components with proper measurements,
rather than just depending on listening, which could just be placebo or halo
effect. Don’t just look at the brand! I’ve bought a famous manufacturer output
transformer and it is actually much worse that something I bought cheaply from
another manufacturer, albeit this “another” manufacturer is only with a few
years of experience in the market where the previous one was there since I
cannot recall when.
Measure them, characterize them, choose those that only meet
your specification and criteria, and make your own brand and taste! Then you
will reach the master level of building that holds both theory and practical of
audio equipment building.
Just to let you know how unique this is – some winders don’t
even use insulation in between layers, or do parallel winding, or did not soak
the transformer in varnish, or have special varnish formula, or interleave
winding methods that minimize stray capacitance for absolute coupling, and etc.
All these will create their signature sound, and therefore you’ve so many
brands out in the market. Well, of course, there are more con men than real
master.
J&K Audio Design
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