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Friday, December 20, 2013

Output Transformer

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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