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Friday, December 20, 2013

Power Transformer Quality



Power Transformer Quality

Does power transformer quality matter? What’s the difference between the generic power transformer quality and the power transformer quality made for audio? Does it matter if proper wiring techniques are implemented versus none, since the output voltage and current are correct? 

I can tell you, it matters! What you cannot measure does not translate to what you cannot hear! Just like you cannot see radio waves but it is there and you can hear them once they are properly demodulated. The things that you cannot easily identify just from the looks or simple measurement are:
  • Noise
  • Waveform integrity
  • Efficiency
  • Temperature
  • Safety
  • Reliability
  • Consistency
  • Regulation
All these require skills, know how, planning and proper implementation to get them made correctly, not to mention consistency if the matching quality is to be repeated, especially important for mono-blocks or multiple identical channels are required. 

How the wires are laid on each layers, how the taps are drawn, how the distance are spaced, how the windings are sectioned, how the winding ratios are kept consistent, how the wire sizes are determined, how the termination is done, how the wiring planning is done, how the resistance versus length versus size are calculated for the transformer, how the inter-layer insulation are laid, how the inter-layer insulation materials are chosen for different layer (yes, it is different between each layers), how clean is the winding environment, how clean when the windings are made, how tense or how loose the wiring is made, how the transformer is prepped for varnish soaking, how the varnish mixture is rationed, how the transformer is baked to dry, how the electrostatic shield is added (if yes), and how the voltage versus current is adjusted to meet regulation requirements, how the compensation is after transformer temperature rise from initial power-on, and many more.

All these, will impact the power transformer quality. With all added up, it will be very significant, and that’s where all the differences mentioned above come from. There is no free lunch, no short cut. Quality comes with sacrifice. 

Nowadays a lot of transformers tend to rattle or hum after some use. This happens even on those famous transformer manufacturers. I’ve encountered some when I used some isolation transformer for my system. I believe you heard that some will ask you to move your isolation transformer outside of the listening room due to hum. This is because the winding method or core design is not done properly. 

Transformer hums because of 2 reasons – the core hums, or the windings vibrates. The core hums could be due to insufficient winding and over-current causes it to produce hum. If it is wiring that vibrates, it is due to improver winding technique or insufficient varnish soaking causing empty space in the winding for the wires to vibrate. All these have solution, but it will not be covered in this page.  
Why does it only hum after a period of time? Well, it could be that the insulation material has aged (inferior quality materials will age faster), the filling or damping material has loosened or hardened (Insufficient filling? Wrong mixture? Not dried properly?) and therefore it starts to hum and gets worse with time. Therefore, it is important to get the transformer from the right source. 

For tube rectification, even more need to be considered as tube rectifiers demand a certain resistance in order not to overload the tube by restricting the current flow to the tube. If the winding resistance is too low, a series current limiting resistor(s) needs to be added. Also, the rectification scheme needs to be taken into consideration as different scheme will draw different AC current on top of the DC current. 

So, have you taken all these into calculation when you customize your power transformer? Or is the on-the-shelf power transformer considered all these when they make this product for you?
Don’t think that you will not hear the difference, you will, not matter how high or low end your system is. It becomes even more apparent when you’re using high efficiency speakers or single driver crossover-less drivers. Nothing can escape. 

Power transformers matter. Power inductor / choke matters. All the transformers on your amplifier matter. Don’t just save on using inferior transformers and loose the quality you’re supposed to get. A small change can make a big difference.

J&K Audio Design

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