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Tuesday, December 17, 2013

Transformer Quality



Transformer Quality 

Technology advances, but why do we perceive that performance or quality over price ratio has dropped drastically? We could buy really good quality stuff in the past with just little money but nowadays quality comes with a super high premium. 
Winding switching transformer

In this article, we are going to talk about transformer quality. Transformer quality is deteriorating everyday as we speak. For the sake of earning more return, higher ROI, high volume manufacturing, quality is compromised by some of the manufacturers. It may look OK on the outside, but it’s just crap in the inside. Or worse is such horrors are hidden behind a nicely portrayed designer chassis. Do not consider potted transformer to be premium! 

Many has suffered, many has been conned by such nicely decorated exteriors. We do not know what’s well hidden inside (transformer potting) until something goes wrong! We’ve suffered before from a few famous local winders / distributors in our country, not just from overseas – you know where. What was sold to us are just plain junk that is LOW-FI, not HIFI. Now we take no chances. We only get from reliable sources. We constantly look for new vendors with quality and reasonable price offerings. 

In addition, potted transformers are bad in dissipating heat and therefore cause the reliability and longevity to be shortened extensively. Transformers love to radiate heat as much as possible to cool the wires and core down to prevent premature breakdown or disintegration of the material over time. We would not recommend potted transformers. 

We’ve seen puny little transformer hidden inside a huge metal can. When you knock at the can, you can hear echo coming out. Now that’s really bad news for those that bought such transformers. Some cases that do not sound hollow, they might be filled with (heavy) filler too, don’t be so happy first! For some that already has crappy outlook, please expect the internal (where you cannot see) to be much worse since they already do not care externally, why would they care internally? 

Quality repair is getting rare too. Repair services are scarce nowadays, especially good repair technicians. Repairing potted transformers will be expensive too since removing them from the cases / pots will be very difficult, not to mention cleaning up the potting compound will be very messy / dirty / difficult. On top of that, repaired transformer needs to fit the original pot! Proper transformer with the right specifications for the job might not fit the original enclosure as they’re usually bigger in size! Therefore, repairing such transformers needs skills and experience, and such repair cost will be high due to all the work involved. Making a brand new transformer will be easier and cheaper! Some will just ask you to buy the original transformer from the OEM that costs a bomb!

The returns will be huge for those heartless crooked manufacturers since they pay lesser for the cores, wires, time due to poor workmanship, and etc. You save on buying cheaper transformers but you lose big time on quality, reliability and outcome. Trust me; there are really such conmen out there! 

Now, do you want to end up in such situation with inferior transformer quality? We definitely don’t. We’ve paid too much ‘tuition fees’ and we’ve promised ourselves to suffer no more. 

Others usually use H-core that is ~0.5mm thick, which is not as good as the Z11 core. So what you should do? Go learn on how to differentiate the difference between the core materials. Usually Z11 core is thinner and greyish matte (non-shiny) in finishing. If it is potted, good luck and only buy from reputable dealers.  Do be careful even if does not look shiny. It might just be a smart and good paint “con” job. If it feels too hot, it probably is inferior in quality.
Winding on bobbin
Power transformers for tube amplifiers will be harder to make due to the multiple taps for high voltages, low voltages, filament voltages, bias voltages and etc. High voltages require more windings too for voltage step-up. For such transformers with many windings, insulation job must be treated with care, to isolate the high and low voltage windings, and also the tap outs need proper care to avoid short circuits. These are all hard work! 

Such complicated transformers will be prone to mechanical vibration or hum if it is not designed properly. Some manufacturers used a lot of potting compound or glue to hide such design issues or defects as a cover up. These transformers will not last very long. Vibrating transformers will cause the wire insulation to weaken faster and cause shorts. Only properly designed high transformer quality will not have such problems and will last much longer than the rest. 

Real scenario: potted transformer is sent for repair but the original core is replaced with another on-the-shelf transformer instead of being repaired. So, when you send for repair, do look for signs that your transformer is being repaired or replaced.

  • Weight difference – too light?
  • Duration of repair – too fast?
  • Price – too cheap?

The value is all gone when the original core is lost. You will not get back what you had before the repair. 

There’s another case that the power transformer we received for repair has not gone through varnish soaking at all! Such kinds of transformers are unsafe. Do not use them! You can observe it easily. Just see if there is any varnish residue on the exterior or at the windings. If it looks like there is no varnish at all, don’t buy them! Varnish will fill up all the air pockets and protect the power transformer from moist and also strengthen the insulation. 

Are toroid transformers always being better than EI core? Not necessary. Some toroid transformer winders will just wind the transformers from start till the end with a single wire, and without having insulation layers, coupled with potting material, will cause the transformer to overheat or short circuited in a short time. Use with precaution! 

Important tip: if your transformer core looks bright and shiny, don’t be happy. Usually these are the low grade cores. Although they look nice, they waste a lot of energy.
  • Poor method of tapping out from the windings – wrong use of insulation methods will just short out the taps very fast. Proper calculation is needed to determine the insulation + thermal strength needed for each and every case. Some just apply the same standard for all the transformers they make, for high or low voltages, which is just darn wrong.
  • Misaligned core, shiny core could mean low quality core that has very high loss = burns electricity even if there is no load, beware!
  • If it looks funny, then trust your instinct, it probably is, do not use or buy! Such transformers probably do not contain good workmanship and therefore the quality or outcome will not be good. Reliability will be questionable too.
Nowadays we found that some transformers are using unknown paper insulated with insulation tape to replace imported Kraft paper dedicated for transformer use. Such insulation strength will not be sufficient, especially for high voltage tube amplifier applications. We will not do so. Such build will malfunction in a very short period of time. 

Some winders cut corner buy using a smaller core, lesser core lamination, lower quality / grade than needed. Perhaps the core prices has gone so much expensive that for them to make “MORE” money, they’ve to go to such extent. Such method will make the transformer very hot and will age faster. Or they might mix core materials together to appear as high quality cores. One can only know if they dismantle the cores – which one rarely does until it is sent for repair. Who loses? You, the consumer! Ethical manufacturers are getting lesser and lesser as we speak.
Kraft paper

Using plastic film as inter-winding insulation – no! It saves a lot of cost and is very easy to make. We do not use plastic films. We use the correct insulation paper material for inter-winding insulation for utmost safety.

Some customers may complain that why our transformers are more expensive than the generic transformers in the marketing. We wish to explain here that out transformers are all made with the highest standards and the quality is reflected in the price. We’re still very competitively priced compared to the famous European or American brands. You are paying for the value – reliability, longevity and sound quality. 

If you have suffered the same fate of poor transformer quality, please feedback and let us know where it comes from and what happened. We need to educate our fellow audiophiles and DIYphiles on such vendors.

Some sharing if pictures below:

Poor fixing for output taps - no insulation too!

Badly wound high voltage winding.

Badly wound low voltage high current winding.

Burn insulation layer - insulation uses normal tape!

Burnt Kraft paper.

Burnt transformer.

Burnt low voltage high current winding

Burnt transformer winding

Poor core stacking

Misaligned core stacking

Poor core stacking - misaligned too!

Misaligned core stacking

Misaligned core stacking



Badly done output taps.

Output taps without proper fixing - short circuit and arcing risk!

Poor output tap


No insulation for output tap, short circuit risk!


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