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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!

J&K Audio Design

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
* 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%.

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

Friday, April 10, 2015

ALIS-5SE Ultimate Review

Nothing is more satisfying than reading good comments from our users online. Please click the below link to see (or to participate, ask questions, feedback, comment) the actual thread at diyaudio.com. 

Below are some screen captures from the original thread for your reading pleasure (at least is our reading pleasure. It is very well written. We simple love it.

ALIS-5SE Ultimate at diyaudio.com

ALIS-5SE Ultimate user comments
ALIS-5SE Ultimate Sound Description
ALIS-5SE Ultimate comparison with Tango XE-20S?

We hope to see the comparison results with Tango XE-20S that is an Orient Hi-B C core OPT soon. It will be an interesting comparison. It will be clash of the Titan with a newbie. :)

J&K Audio Design

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.

Monday, April 6, 2015

High Grade Power Transformer

Another high grade power transformer (Level 4 Power Transformer) is in the making!

This unit is made for mini-power-amp or line-stage usage (medium VA) and therefore we still have suitable transformer case for this high grade power transformer. Our vendor for transformer case has ceased production and we have only a limited quantity of small - medium size cases left. The large case is used up and we do not longer have them unfortunately. For larger transformer, cases will have to be custom made and that takes time since it involves 2 stages process - producing the chassis and finishing (powder coating). 

As usual, Level 3 and 4 power transformers uses only the best of the best from J&K design group. Users had commented that they exceeded even the high grade power transformers made using Z11. One has even found that Level 3 Super Hi-B C core power transformer actually produce sound like 2x the output power compared to audio grade Z11 power transformer. No kidding - 2x the output power!

Computer Engraved FR4 Plate for Solder Tags

High Grade Power Transformer
The solder tags are silver plated copper for lowest resistance and better sound. It is way much better than standard brass or tin-plated copper tags. The thick FR4 plate as base of the tags also helped to reduce vibration to the minimum.

Level 4 Power Transformer

Silver Plated Magnet Wire
The windings are aligned neatly for absolute best energy transformer between primary and secondary. This ensures the efficiency is the highest where energy draw will be optimal for 50-60Hz use.

Teflon Insulation between layers
Teflon tape is used instead of Kraft paper for better / higher insulation strength, lower weight, and smaller bobbin.

Tight coupled wires
Perfect wind. No voids. No overlaps. No untidy wires. This helps to have better electrical, thermal and mechanical stability = better sound, longer life, lesser noise.

Medium size transformer case

It is unfortunate that this vendor stopped producing this type of cases. It looks nice, works fine and sounds good. We have very limited old stock left for small-medium transformers. For large transformers, we will have to go for copper sheet shielding and customized chassis. It takes time but that's the best we have for now. 

The owner shall be delighted visually and sonically! Prepare to witness the perception of doubling the output power! 
J&K Audio Design