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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

Product Lists  

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Level 3: depends on type, size and complexity. Email us for details.
Iso-trans: link 1, link 2
* 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.




Tuesday, April 21, 2015

Audiophile Isolation Transformer

Looking for an audiophile isolation transformer - this is the place to get it! We have been promoters of high grade cores and we will use high grade cores for our isolation transformers as well! Now this is truly an audiophile isolation transformer! 

Some goodness are mentioned here:
  • Reduce mains interference (in and out!)
  • True balanced power
  • Removes power line noise
  • Eliminates ground loop
  • Reduces radiated fields from equipment or cables
  • Soft start / reduce turn-on surge
  • Reduces interference between equipment

We offer several grades of high quality transformer cores that can be used for different types of application. Usage of other lower grade transformer cores will not produce the same results and might even add unwanted properties to the sound. Use others at your own risk! 
  • Z11 and H14, EI core, up to 1KVA for single unit, 2KVA for double unit
    • Good for medium high power applications.
  • Super Hi-B double C, up to 350VA for single unit, 700VA for double unit 
    • Good for medium-low power applications.
  • Z11 grade, toroid core, up to 2KVA for single unit
    • Good for very high power applications. 
  • Other higher KVA, please contact us.
Tips: If you are worried that using isolation transformers is direct in the power path, then you can use it ANOTHER WAY ROUND! If you know your NON-audio related electronics devices or equipment are causing the mains noise, apply the isolation transformers on them! This will prevent noises generated from these equipment to pollute your mains! Example - equipment with SMPS (Switch Mode Power Supply), phone chargers, TV (yes!), computers, modems, PC speakers, mini-HIFI, and etc! If you are worried about power wastage, when you are not listening to your HIFI, just bypass them with a switch during normal time.

It is best to connect only a single equipment per isolation transformer and size them accordingly. Having all your gears connected to a single unit of isolation transformer is less ideal too. Equipment themselves generate noise. Putting all of them together is going to cross-pollute each other. Underload or overload are not desirable. We aim to isolate not just the noise from mains, but also noise from the connected audio gears. 

It is recommended to load it to ~75% to have enough headroom although our units are tested to 100% load or more. Isolation transformer is a transformer. It does not act like a regulator unless additional circuit and design are built in to keep the output at regulated voltage desired by user. It has a standard primary:secondary ratio. 

Standard unit are 1:1 and output voltage is specified at 50% load. This means that at 50% load, the output voltage will be same as the input voltage. If it is underload, the output voltage will be higher and vice versa. Other manufacturers do not tell you this but we do. It all works the same. So, please specify your needs and usage model when you order. Other working model or multiple taps can be built if your mains have other issues like constant low or high voltages issues and such, please email us. 

Notes: additional features can be added per customer requests.


This is how a standard configuration of our universal isolation transformer meant for 240Vac operation. It can be made for 120Vac, 110Vac or 100Vac operations too with different primary and secondary voltages. 

This is configured for 120Vac output operation.


This is configured for 240Vac output operation



This is configured for 240Vac true balanced mode operation. The goodness of balanced mode is well covered and written by a lot of folks online. You can Google for it. Some are mentioned here below:
  • Balanced power lowers noise floor.
  • Increase if dynamic range for up to 15-20dB. 
  • Keep ground plane clean.
  • Reduce reactive current in ground line (reduce noise floor).
  • Cancel noise by CMR method (common mode rejection).
  • Reduce radiated fields on cable and equipment.
Notes
* It is like how balanced audio mode are used to reject noise in professional audio applications. 
* Reactive current or noise on ground line is not something power conditioners, regulators, ground scheme or cable can resolve.

Enough with all the talks and theories. Let's look at some pictures of our custom builds!

Full aluminum chassis (non-magnetic - no hum / rattles compared to steel chassis)

Thick front plate with voltage indicator
High quality IEC sockets
Others IEC is only 76g.
Ours IEC socket is 115g! (others can be used per user request)
IEC socket





Cryoed gold plated copper IEC inlet with screw terminals (solder-less, others can be requested)


Military grade fuse holder (30mm type)
Solid wood plate with copper terminals

Optional - discrete custom made modular DC filter and EMI/RFI filter

Z11 EI 1KVA Isolation Transformer Unit

Finished Unit

4/21/2015

J&K Audio Design

Product Lists  

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Level 3: depends on type, size and complexity. Email us for details.
Iso-trans: link 1, link 2
* 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.

Wednesday, April 15, 2015

2 coil choke


What is a 2-coil choke? It is a choke with 2 windings wound onto the same iron core. The advantage of 2-coil choke is that it can be configured in different ways, according to the user desired effects! 
Above is how a 2-coil choke symbol looks like. It is having 2 coils wound on the same iron core, as shown in the above picture.

There are four ways of connection that I can think of right now for tube amplifier power supply usage. 
  1. Series mode
  2. Parallel mode
  3. Common mode noise rejection
  4. Differential mode noise rejection

Let's take a 10H 100mA 50 Ohm DCR choke as example:
Mode 1 - 10H with 100mA capacity and 50 Ohm DCR

Mode 2 - 2.5H with 200mA capacity and 25 Ohm DCR
Mode 3 - mH in inductance, 100mA, usually use in AC circuit only
Mode 4 - 10H with 100mA capacity and 50 Ohm DCR

Such 2-coil power supply chokes are made to couple well at low frequency, usually at double the mains line frequency of 50/60 Hz (results of full-wave/bridge rectification). Mutual coupling between the coils will be low at higher frequencies, and will act as 2 different chokes at higher frequencies. This behavior can be used in advantage to different applications.

What are differential mode noise and common mod noises? I think you guys can find that out using Google. There is no need for me to reinvent the wheel again over here. 

Mode 3 will reject common mode noise and mode 4 will reject differential mode noise, simple as that. You can treat them like a differential mode choke (DMC) and common mode choke (CMC) commonly used in power supplies. The only difference here is that the standard CMC or DMC do not pass DC where it works in the AC region before rectification process. For our DC chokes here, it works with DC in mind.
Common Mode Choke

Differential Mode Choke

Do note that for connection #3 - common mode noise rejection configuration, it is usually used in AC circuit mostly. You can apply this in DC circuit too but it does not act as a power supply choke anymore in such configuration. That is, it is no longer a capacitor-input filter in the above diagram. You will need to add another choke to provide the usual filtering function to complement the "common mode choke".

Using such 2-coil chokes will be beneficial to gain extra edge on getting a quieter power supply for your amplifiers. Do not forget this when you are designing your next amplifier. An example of application would be as follow:

  • 3 stages: rectifier -> 2-coil choke in series or parallel mode -> 2-coil choke in common mode config -> 2-coil choke in differential mode config. 
  • 2 stages: rectifier -> 2-coil choke in differential mode config -> 2-coil choke in common mode config 
  • And many more!
Just for your reference, an open square frame refurbished Permalloy double C core choke of 1-coil choke of 8H - 10H 300mA is U$120/pc now, and a 2-coil version is only U$140/pc. The price difference is minimal yet the benefits are many folds! 

Now, go order a 2-coil choke and replace all the chokes in your amplifier to lower the noise floor and improve the sound!

4/15/2015
J&K Audio Design

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Level 3: depends on type, size and complexity. Email us for details.
Iso-trans: link 1, link 2
* 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.

Tuesday, April 14, 2015

Low Cost Tube Preamp

Today's topic is about low cost tube preamp.

Everything is about money, money and money nowadays. With the ever rising living cost, coupled with poor money management of you know who, added with GST, it is harder and harder to survive nowadays.

What can we do if we still want high performance with little money involved? Well, you've got what you ask for today! When people talks about tube preamp, the first thing that associates that with high quality is tube preamp with output transformer, WOT Preamp as some call it. 

Wait a minute. Output transformers are expensive, aren't they? Tube preamp or linestage output transformer are expensive too, right? Especially the high performance ones! Well, you are right! Or, you were right, till we offered the ALOS series of output transformers.

I believe this has slipped some of our follower's eyes. It's alright. We are re-introducing this baby here again. It is being disguised as Head-Phone output transformer, that's why it slipped most eyes that wanted a tube preamp output transformer. Take a look below! 

ALOS Output Transformer link

ALOS-75HP Power: 2W(20Hz) Single Ended
Bandwidth:
* Pentode: 20-65kHz -3dB
* Triode: 10-60kHz -2dB
Primary: 7.5K; Secondary: 0-150-300 Ohm
Core: 35H360 (H14) EI66
Pri. DCR: 506 Ohm(B-P)
Sec. DCR: 38 Ohm (0-300 Ohm)
Primary Inductance: 50H(40Hz, 5Vrms)
Primary Current: 40mA (50mA max)

* Matched in actual operating conditions.
* DCR <1%, Primary Inductance <5%.
U$99/pr

Yes, you got it right! It is only U$99/pr. Of course, with such price, you can't expect too much out of it too, but the specifications are very decent, and decent enough to be used in not just low cost tube preamp where it can be considered as high performance tube preamp where the preamp output transformer actually boasts of 10Hz - 60KHz @ -2dB frequency response in Triode mode. 

Tell me, how many speakers actually can reproduce such frequency response? Very few. And for those who owns these speakers, they don't mind paying for our higher end output transformers with better specs anyway. 

This low cost tube preamp output transformer has a highish primary impedance of 7.5K with a handsome primary inductance of 50H. It comes with primary current of 40mA too. That is good enough for most of the preamp tubes out there, or even small power tubes. If you use tubes with low Rp (plate impedance), you can actually widen the already quite decent bandwidth. 

The secondary comes with 2 taps, and is configurable to single ended output or balanced output. The 150 Ohm tap is the center-tap, the 0 Ohm and 300 Ohm taps are the +/- taps. Now this gets even better, right? It is now a low cost high performance balanced tube preamp with output transformer! I bet a lot of the commercial can't even come close to your design if you do it right. 

The output impedance can be configured to 150 Ohm or 300 Ohm, which is low enough for most power amplifiers, even solid state versions. What about the gain of this tube preamp output transformer? x = gain.
  • Z2/Z1 = x2
For 300 Ohm output, x = SQRT of (7500/300) = 5 (5:1 step down)
For 150 Ohm output, x = SQRT of (7500/150) =7 (7:1 step down)

If you power amplifier needs 2Vrms for full power, then anything tube with a gain of 7 or more will be sufficient for this low cost tube preamp. I can already think of many in my mind - 5687, 5842, 6C45, EL84, EL83, 6DJ8, 6922, 7119, E88CC, EC88, C3M, C3G, and many, many more...

With the low pricing of ALOS-75HP, one can even buy 4 units and make it a true 4 channel preamp! They can drive 2 monoblock power amplifiers and 2 subwoofers, or 4 monoblock power amplifiers for bi-amping! Fun right?

So, why wait, go ahead and order 4 units from us for your low cost high performance tube preamp project! 

P/S: do not forget that this can be used as headphone output transformer too!  

J&K Audio Design
4/14/2015

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Level 3: depends on type, size and complexity. Email us for details.
Iso-trans: link 1, link 2
* 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.




Wednesday, April 8, 2015

Super Hi-B transformer review

We'd like to express our gratitude to David V for writing a review on our Super Hi-B double C core power transformer! We were blogging about how to increase your power amplifier by 2x perceptually. Now the answer is revealed here. 

What you read below has only 1 edit being done - changing "Hi Hi-B" to "Super Hi-B". We were calling it Hi Hi-B previously but Super Hi-B will be an easier term to use and therefore we've edited the content for that. Other than this, it is 100% original from David V. 

Here goes:


300B Mono-block Amplifier

Super Hi-B Power Transformer

Tango NC20F and Tamura OPT

Solid Wood Chassis




My acquaintanceship with J&K Audio Design happened by coincident early last year in 2014. I was searching for some information on power transformer in the net and this company called J&K Audio Design came to my attention. I was intrigued by their pictures showing how their transformers were wind, sealed and potted. From their pictures and their working processes, I know the transformers are going to be durable and long lasting. Soon I got in touch with the Ken of J&K Audio Design and enquired my need to order a pair of replacement power transformers for my 300B amp. Ken came back to me suggesting I use a pair of Super Hi B double C-core power transformers. He quoted me a price for a pair of potted version. The price for this Super Hi B double C-core power transformer is not cheap but I'm adamant to get a pair to try them out myself and see how good they are! I placed an order and they finally came after two months of waiting.

During my break during the 2015 CNY, I managed to swap out my original Z11 power transformer from my 300B monaural amp and in came the Super-Hi B C-core power transformers.

My 300B monaural amp is a direct couple SE with the 5687 or 6900 as the driver tube onto an interstage NC20 that finally drive the 300B to Tamura Amorphous OPT. The design was inspired by April Sound 50 amp and I'd it for several years but never am satisfied with the end result until I got it replaced with the J&K power transformers. When the power transformers were replaced and I  powered up the amplifier, the power output from these 300B gave me an impression that it's unusually powerful. I'd the normal listening level that I used to play but the sound level from my speakers seems to be twice as loud than when I were using the Z11 power transformer with my Tannoy GRF speakers.

I have about 50 hours of run in since replacing the power transformers. The music flavors of my liking are jazz, chamber, female vocal and orchestra (classical). Here are samples of some of the music and my general listening opinion.

I'd auditioned some live performance recording like a Jazz version of 'When I fall in love'. The sound coming out of my Tannoy GRF was remarkable, as though I was in the room where the piano was played. I can really feel the ambient, the reverberation of the piano's notes from the Steinways & Son piano. I also listened to the ODaiko, a traditional Japanese drum pieces. The rhythm, the pace and the vibration of the drum is tight and vivid. I can really feel the energy from the drum. I almost forgot I was listening to a 300B amp, as the music coming from it sounded as powerful as a push-pull 6L6 amp, but with more clarity, warmth, dynamic and detail.

I believed the J&K Audio Design Super Hi B C-Core power transformers played a big part in the improvement of my amplifier. I also sampled on some Violin piece (Zigeunerweisen Op.20 by Anne-Sophie Mutter), live Guitar piece (Lion Lai Small Town by Japanese Guitarist Kazahito Yamashita), Cello piece (The Swan), Orchestra pieces like William Tell Overture and Radetzky March Op.228. The music coming out from my 300B amp was fast, clean, dynamic, and transparent with superb imaging and they never run out of juice even with complex pieces. One would never believe it's coming from a 300B amplifier.

The J&K Audio Design Super Hi B C-core power transformer has really bring out the best of the
Tamura Amorphous OPT. My previous Z11 power transformer was lacking in some attributes that prohibit the OPT to perform optimally. My experience convinced me that for an outstanding triode SE amp, the choice of power transformer is as important as the OPT that you are using.

The J&K Audio Design Super Hi B C-core power transformer is not cheap but it's worthwhile. If you plan to upgrade your amplifier, I would suggest you have your OPT, power transformer followed by internal wiring, then the output tubes in that order of priority.
Here are some pictures of my 300B amplifier.

By David V 6th April 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.  
* 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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* 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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