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Monday, November 6, 2017

Penang flood

Penang island just experienced the worst flooding in the decade, perhaps even century! Georgetown had became Teh Tarik Town as most of the streets were flood with orange colored water from the downpour over the last weekend. Some areas even had chest deep water level. 

A lot have lost their homes, valuables, vehicles, and worst, some had lost their love ones. We're among the lucky ones where our operations and staffs are only slightly affected. We suffered losses due to damaged raw materials and finished goods. Still, these are only monetary losses. Thank god for that. Undelivered orders will be delayed as affected units will be scrapped and redone due to this natural (or man made even - global warming!) disaster.

Still, we must not forget the unfortunates and we pray deeply for them. 

Attached below is just the tip of the iceberg on how Georgetown was affected.

God bless the Penang and all flood victims. 

J&K Audio Design

Friday, November 3, 2017

GM70 Amplifier Review

GM70 tube amplifier review (a short one).

Domnic uses full set of transformers from J&K Audio Design - the GM70 output transformer, separate power transformer for B+ and filament transformers. 

Enjoy the pictures - very nicely done!

Short and sweet comments from Domnic!

The hum & hissing are not related to the transformers but the design of the amplifier. After several emails between Domnic and us, this issue is fixed by adding some additional circuit to the amplifier. The amplifier is as quiet as the deep wide universe now, and he's a very happy camper!

Some GM70 amplifier internal picture for those more technical minded. A lot of audiophile components are used, such as Mundorf electrolytic capacitors, Jensen PIO coupling capacitors, Kiwame carbon composition resistors and of course, full set of J&K transformers.

Again, this is as honest as it can be - review from real user! No alteration of the customer posts have been made.

J&K Audio Design

Saturday, October 28, 2017

Out of office

Hi guys,

We will be out of office for 1 week, on a business trip to China, starting 29th Oct'17.

Email access and response will be very slow as a lot of the websites we use are blocked in China, such as Google based applications and Facebook.

Apologies for the late responses and any inconveniences caused is very regretted.

We will get back to you once we're back to office week after next. 

J&K Audio Design

Saturday, October 21, 2017

Quad Core Transformers

Return of the Quad Core Transformers 

3 years ago, we started making quad core transformers (or quad C core transformers) with refurbished C cores (amorphous cores, Permalloy / nickel cores). As they were refurbished C cores, the sizes and cores are not matched, and the electrical properties of the C cores are quite hard to control. We rate them as our entry Level 0 transformers at that time. You can see the previous links of these Quad Core (Quad C Core) transformers here:

We discontinued the above Level 0 Quad Core transformers as it did not live up to our expectations and quality control. After 3 years, we decided to re-introduce them! This round, we shall offer them as Level 2 transformers, and we are using brand new C cores to make such Quad Core (Quad C core) transformers. The types available are:

* Quad C Core / Quad Core Output Transformers
* Quad C Core / Quad Core Interstage Transformers
* Quad C core / Quad Core Input Transformers 
* Quad C core / Quad Core Super Charger Input Transformers 

They are about 35% more expensive than standard Level 2 transformers. They are much more difficult to make, and the efficiency is higher as the windings are surrounded 360deg (almost) by the cores. You can use the below link as price reference. Email us at the form on the right if you need an actual quotation.

For those transformers that are not on the list, email us for further details. We cannot list all of our transformers in the blog, apologies.

The new Level 2 Quad C Core transformers are MILES better compared to the 2014 version (which is a Level 0 type). The C cores are brand new, and have known electrical / mechanical properties, and therefore the end results are better - wider bandwidth and flatter frequency response.

Do note that Level 2 Quad Core output transformers and Quad Core input transformers are only available in potted format as Quad Core output transformers are hard to secure with square frames. We'd need to pot them to ensure there are no movements in the C cores to preserve the original design parameters. 

Hear the unheard! 
Go go go custom made audio!

J&K Audio Design

Sunday, October 15, 2017

Isolation transformer effectiveness

Many had asked us, you have so many types of isolation transformers, which should I choose? 

Instead of repeating ourselves again and again (not that we're not willing to, but just to save everyone, and our time), here goes the effectiveness rating, from our perspective, from low (bad) to high (good), with some comments:
  1. Toroid isolation transformer (for HT, audio OK too but not warm and clean as C or EI)
    1. Up to 3.5KVA for highest grade toroid core (other grades with higher KVA are available but not recommended)
    2. >3.5KVA, go for parallel toroid for lower impedance 
  2. C core isolation transformer (for audio and HT) 
    1. Up to 1KVA (bigger size, can be custom made, up to 3KVA)
  3. EI isolation transformer (for audio and HT)
    1. Up to 3KVA
  4. C core ultra isolation transformer (for audio and HT)
    1. Up to 1KVA (bigger size, can be custom made, up to 3KVA)
  5. EI ultra isolation transformer (for audio and HT) 
    1. Up to 3KVA
Some articles about ultra isolation - article 1, article 2

OCC copper magnet wires (Ohno Continuous Cast) transformers are available for #2 to #5. OCC comes with a hefty price tag though. 

Benefits of OCC - lower DCR, better dynamics and clarity. We often use OCC for our output transformers, but for true audiophiles, those that hear a difference with high grade power cords, this is definitely better, and higher ROI compared to using OCC based power cords. 

* Balance or single ended outputs
* Multiple-taps isolation (explanation below) 
* Potting/frame
* Multiple shielding (electrostatic, primary/secondary, secondary/secondary
* Can be made as power transformers with isolation/ultra-isolation for SS and tube amplifiers


What is multitap-isolation? Normal isolation transformers have only 1 single set of outputs, say:

- Primary: 0-240V-G
- Secondary: 120V-0-120V (balanced)

Multitap-isolation is as follow:

- Primary: 0-240V-G
- Secondary 1: 120V-0-120V (balanced, isolated/shielded from 2/3)
- Secondary 2: 120V-0-120V (balanced, isolated/shielded from 1/3)

- Secondary 3: 120V-0-120V (balanced, isolated/shielded from 1/2)

This way, instead of having multiple gears connected to a single secondary, each output is connected to 1 set of secondary to make 3 sets of ISOLATED outputs. This way, the CDP, tube preamp, and DAC (for example), are isolated from one another as they are connected to different secondary windings instead of connected altogether in a normal isolation transformer unit where all the outputs are connected to a SINGLE secondary. 

This is a MUCH better isolation scheme than normal paralleled output on-the-shelf isolation transformer unit. Yet, it is more cost effective than having 3 units of separate isolation transformer, which is the ultimate way one should do it, eventually perhaps.

Go go go, custom made audio!

J&K Audio Design

Type 50 Amplifier

Supercharger amplifier with type 50 tube, anyone? Want to listen to how a pure type 50 tube amplifier really sounds like without other tubes to color it? Well, Sakuma style is a good example, using 50 to drive 50. Due to the scarcity of type 50 tubes, let's not waste the 50's. 

Note: One can use ANY power tube to replace type 50 tube in the below example, DHT, IDHT, pentode, tetrode, or any power tubes, even power transistors! Since we just heard the good news that Elrog is coming out with type 50 tube, now is a good time to look into this DHT tube!

Caution: Not any input transformers can be used in such circuit. Ordinary input transformers may not have enough core volume to sustain high voltage swing (usually <10Vrms). Ordinary input transformer primary winding may burn if driven by a power amplifier. Special input transformer is required for such purpose.

Some previous reading:
Supercharger Amplifier
Step-up input transformer

Type 50 tube amplifier

Take a look at the schematic above for type 50 tube. It is as simple as can be. Of course, you can complicate it a bit by making it fixed bias, add more bypass capacitors, LED bias, regulator tube bias, and etc. The power supplies for B+ and filament are kept out for the moment. Let's just keep it as is for now for simplicity sake.

There are 2 resistors that MAY be redundant too - the grid leak and the grid stopper. Grid stopper - prevent tube oscillations. Grid leak - as described in type 50 tube datasheet, needs to be <= 10K to protect the type 50 tube. In this case, it may not be necessary since the input transformer secondary acts as the grid leak path. The transformer secondary will be the least resistance path for the type 50 tube grid to take even if you connect a 10K resistor. Also, if the resultant waveform is not having severe ringing (even if it rings), the grid leak resistor, which act as the load for the input transformer, will tame the ringing. For type 50 tube, with input transformer, it is better not to have the grid leak resistor if possible.

Let's take the operating point of type 50 tube as 425Vdc B+, -70Vdc grid, 55mA, which is quite commonly used by a lot of folks. This needs about 140Vpp to drive type 50 tube to full power. That produces about 4W of undistorted power output to the load (your definition of undistorted may be different, especially the SS folks).

Say, let's use a standard source, which is an ordinary CD player, or DAC, with 2.8Vpp output and 600 Ohm of output impedance. To get sufficient Vswing to drive type 50 tube to full power, one needs a gain of = 140Vpp/2.8Vpp = 50. Wow, that's a lot of gain required, and is not feasible at all here. Let's drop the standard source.

Let's go for a preamp instead, say a 5687 simple tube preamp with output transformer, having output impedance of say 150 Ohm. 5687 has a u of 18, and is usually loaded with 5K primary impedance. With that, the resultant gain would be root of 150/5000 * 18 = 3. Not so much eh, but is good enough perhaps? Let's check.

With 50 / 3 (gain of tube preamp), we get to gain of 16. Hooray! STU-001 here has a gain of 1:18! Just close enough, with a little bit more for headroom or circuit tolerance. 

Conclusion? As previously mentioned, a very high drive strength preamp is required if a supercharger is driven. If tube preamp is used, something with output transformer and higher gain is required. The above example of using a simple 5687 with output transformer looks like a bare minimum supercharger amplifier can tolerate. 

Enjoy tube tasting! 

J&K Audio Design

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Level 1: link 1, link 2, link 3, link 4

Level 2: link 1, link 2, link 3, link 4, link 5, link 6, link 7, Link 8, link 9

Level 3: depends on type, size and complexity. Email us for details.

Iso-trans: link 1, link 2

Power-trans: link 1

* 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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