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Friday, April 24, 2015

High Quality Output Transformer Design

We have received a lot of emails since someone posted the listening results of our ALIS-5SE Ultimate output transformer in www.diyaudio.com forum. Some that like more theories and technical explanation asked further on the design of this unit. Instead of making individual replies, we decided to write a little about our designs.

Making an output transformer that produces sound is easy. One can even use an ordinary step down transformer, be it EI or toroid, to act as an output transformer. I'm serious! Try it if you do not believe me. To make high quality output transformer, then it is another different story. It is not very difficult either, since it is not something new under the sun. It has been there for over decades. To make the absolute best quality output transformer, that's the harder part.

We have been taking customize orders for quite some time, and we can say that we've understood the several transformer cores we use in and out. Still, to optimize them to match customer's, especially those Level 3 wide bandwidth, minimal phase difference and good sounding (measurements is one thing, sound tuning is a different story, it is an art!) output transformers, is daunting task. For standard designs like 2.5K, 3.5K or 5K, it is no brainer since we have done it for many, many times. For uncommon designs, it often takes us many rounds of build to make the perfect wind. That takes considerable time! 

If the cores are supplied by customers, it is even more difficult. We have to do a trial run, measure the results, correlate it with calculation, and redo again until we are satisfied with the results, or the results match the customer requirements and/or level specifications. This is a time, knowledge, energy, money and resource consuming activities. 

In the past, the output transformers are made with mathematics calculations, formulas, best-known-methods and steps pass down by generations of winders and reference books. This has brought us quite far in producing good quality output transformers. Although so, we will reach a bottleneck where there is just so much a human, or a collective team of human can do. 

In order to optimize the processes and make great (not just good) output transformers, we need to fully master the all the variables in the equation in order to get the same excellent results each and every time. As a history, I come from a world where everything can be mathematically represented. Everything can be modeled up to a certain accuracy for absolute performance in ultra high speed applications, where every little detail will affect the results drastically (we are working in MHz - GHz region). I believe you've heard of SPICE, or MATLAB, right? That's one of the models that engineers and scientists use. 

Matlab
Spice
Simulation tools are not something new. They've been in the marketing for ages! We've even seen GUI tools made out of such programming libraries to design power transformers, chokes and output transformers. Just Google for them if you want to taste some. Such tools are good but they are not comprehensive enough to capture every parameters we need. Customization using the real simulator is the only way to go if you want a full grasp of all the critical electrical and mechanical parameters of an output transformer design. 


 


Imagine putting all these above (not comprehensive!) into the manual design!

Therefore, quite some time ago, we started to apply the same methodology and started modeling and characterizing the real actual results of Z11/H* transformer cores versus theoretical models. We build up the libraries as we make more and more output transformers up to a point where the measured in-circuit results actually matches closely with our theoretical models! On top of that, transformers does not work alone by themselves. They need to work in a circuit where active components are involved and that complicates things further. That, is incorporated into the models as well and simulated as a whole for the absolute best results. 

With this models and libraries, we can actually automate some scripts to run through thousands and millions of iterations to arrive at the absolute best configuration for each and every design! 

ALIS-5SE Ultimate output transformers is the first we employed such technology. The results are fantastic! We were never happier with the results obtained for this pair of EI output transformer. It is approaching the results of even our Level 2 and Level 3 output transformers! It has very low DCRs, healthy primary inductance, low phase shifts, and very wide bandwidth! With such efforts and technology being used in ALIS-5SE Ultimate, we should have categorized it as Level 3 products but we refrained from doing so to give our followers a chance a taste of our sweet success. It is priced very reasonably (a steal!) at only Level 1 category! 


That's how it is done now for our Level 3 output transformer designs using Z11 cores. We even come to a point where we mix some Z11 and H* cores together to obtain the electrical parameters that we need (since we know what is missing with the electrical model) to arrive a balance optimal point! That's where and how the ALIS-5SE Ultimate output transformers were born! 

"What about the C cores?", someone asked. 

I believe you have read in our blog that we were playing with Metglas C cores but we never really did launch it officially. We played with it, optimized it, but still are unhappy with the results in audio applications. The electrical properties are great, but it is just not suitable in our opinion for audio amplifiers as output transformers. We tried with a few other standard amorphous cores, and still we were unhappy with the end results. So what did we do? We ordered customized Nanocrystalline C cores, made to our own specifications and requirements!

We have been toying with the Nanocrystalline C cores ever since we got it. We have made very, very decent Level 3 output transformers with this cores even without using this technology (we were using old school method) and sold quite a lot of pairs worldwide. Since these Nanocrystalline cores are customized according to our requirements, optimizing them with the ordinary traditional non-simulated methods were not that difficult but still not easy either. We can still make great output transformers using old school method alone. Still, the Nanocrystalline is not optimized fully and we have to get this thorn out of our heart. We have to employ this technology for Nanocrystalline cores too!

We had some issues perfecting the model as the electrical properties of the cores shift since the units that come in did not really correlate that well batch by batch. There were some manufacturing process shifts due the alloy composition, annealing and cooling process. We had to reject them and delay some deliveries to keep to the same quality. (Apologies for the delay, guys!) Such deviation causes some change of electrical properties when we make it into output transformers with the existing formula. These cores still make great output transformers but there were still not the best. There were samples that are great, and there were samples that are just good. We want consistent greatness! We want the "bestest" of all!

We spent quite some time calibrating with our supplier and we have to reorder and set our expectations right with our beloved patience supplier until consistent electrical parameter units are reproduced every time. The latest few batches came in and we saw the consistency (close tolerances) in these Nanocrystalline cores. We characterized quite a large samples and finally plugged all these figures into the model. We tried many, many rounds of experimentation with the model versus actual results and finally we can say that we've arrived to the point that the technology is ready, for this Nanocrystalline cores!

Now, we proudly announced that, our Level 3 Nanocrystalline c cores output transformers have just got a new life! They are better than before!!! We are pushing out the release of our current latest orders to deliver on May 2015 in order to intercept this new methodology (sorry guys, it's worth the wait). We shall keep the price the same, but deliver the new output transformers with computerized design process!

P/S: design is computerized only, physical unit are still hand made!

Cheers!

J&K Audio Design
4/25/2015

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* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.  
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* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.

* Our product lines are always improving and increasing. If you do not see what you want, contact us!

* Please email for volume discounts, distributor and OEM pricing.

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