Cobalt Output Transformer

Great news. We have found 2 sets of Cobalt C core good for making 2 pairs of output transformers or high power interstage transformers.

Price is U$1390 / pair for interstage transformers or output transformers, Level 3.

This is chance of a life time since Cobalt C core does not come easily. They are refurbished units and no longer being made. We had some a few years ago and they have run out for some time - refer this link, link.

Now we found 2 sets. Get it quick or it will be gone again. Sorry, we do not sell just the cores.

Hear the Unheard!
J&K Audio Design
9/21/2016

Parafeed Output Transformer

Busy is the only word left on our dictionary for quite some time! Time to update our blog or else people might think that we are MIA.

Since a customer from down South in Australia asked for a pair of parafeed output transformer (parallel-feed), we might as well do an introduction here. Parafeed output transformer is not something new. 

Below is a sample schematic from diy-audio-guide. It is a parafeed tube amplifier designed to operate with 2A3 / 6B4G / 6A3 vacuum tube.

How it works is that the tube load, which is originally a single output transformer, is now split into 3 parts - the load inductor (can be resistor, or CCS too), the parafeed coupling capacitor, and the parafeed output transformer. The parafeed capacitor can be placed on the receiving arm of the parafeed output transformer, or the grounding arm. Both way works but if the parafeed output transformer do not have high insulation strength, it is better to place it at the receiving arm to isolate DC from the parafeed output transformer.

The parafeed coupling capacitance for flat frequency response can be calculated (estimation) as follow:

C = 2*L/(R*R)

C is in Farad
L is in Henry
R is load impedance (transformer primary impedance) in Ohm 

John Broskie from Tube Cad Journal has the formula as follow: 

C  = 159155/(rp + Rload)/Frequency,

C is in µF 
rp is the tube plate resistance. 
Frequency is the cut-off 
Rload is the primary impedance of parafeed output transformer

The most frequently faced problem with single ended tube amplifier is always the output transformer capability (bandwidth). As we have always mentioned, the design constraints of output transformer are always contradicting each other. In this case, the air-gap required for SE operation will work against the primary impedance that is required for better low frequency extension/responses. With parafeed configuration, this is eliminated where we do not need to have air-gap for the output transformer due to only having AC going to the parafeed output transformer, which in turn, make it smaller and better optimized for lower capacitance and leakage inductance. Benefits to output transformer design one of the most important benefit for parafeed configuration.

Of course, there are other benefits as well such as better PSRR due to having a choke as load (hum reduction), having the opportunity to use exotic core (nickel/permalloy, cobalt, nanocrystalline, amorphous and etc) for the output transformer since DC saturation is no longer an issue.

Parafeed is all pros but no cons? Nuh... don't be happy so soon. There are drawbacks of course:

• High quality high value load inductor will be needed since it will experience full audio frequency spectrum instead of 120Hz or 60Hz mains frequency, and provides high impedance at all audio frequencies
• Additional parafeed capacitor is in the signal path
• Tuning may be needed to optimize the inductor / capacitor 
• More tube amp real estate is required
• Etc

Although there are so many drawbacks, they can be individually tackled/resolved (with money), that's the beauty of parafeed configuration! You can have a high quality plate load choke, high quality teflon / oil / film coupling capacitor, and you are half way to heaven!

We had tried parafeed amplifier and they do have excellent low frequency response, coupled with sound that feels louder than the Watt rating. Of course, the sound quality will be dominated by the 3 parts now (parafeed load choke, parafeed capacitor and parafeed output transformer) instead of 1 single output transformer.

For those that are interested to build a parafeed 300B / 2A3 amplifier, you can consider the following output transformer options: 

• Level 1 - 10W Parafeed Output Transformer
• EI Z11 - U$190/pair
• EI Z9 - U$240/pair
• Level 2  - 10W Parafeed Output Transformer
• Permalloy OPT - U$640/pair, potted
• Level 3 - 10W Parafeed Output Transformer
• U$890 for EI Core potted
• U$1090 for Nanocrystalline Double C potted

Hear the Unheard! 
J&K Audio Design
9/15/2016

Peerless Input Transformer Repair

We've repaired a lot of power transformers and OPTs in the past. Chances of repairing input transformers are not has high since the failure rate is less compared to others but we still do get them once in a while, especially those very sought after versions, such as input transformers from Western Electric or Altec Lansing, such as this one that we just received.

The data was quite hard to be found online for this Altec Lansing input transformers. The owner provided the specifications to us after checking with the new owner for Peerless transformers. 

Input impedance: 25K CT

Output: 600 CT / 150 Ohm

This is how it looks like before it was dismantled. It is sealed in some sort of rosin and requires heating before the transformer can be taken out. 

After the extraction, the core lamination (obsolete now) are then cleaned up before it can be reused. The winding and bobbin are discarded as they no longer can be used. Due to the non-standard size of the core lamination, a customer bobbin has to be made to get a perfect fit. Standard size bobbin will not fit properly and there shall be unwanted design deviation that will not get it back to the original condition and performance. 

The original bobbin / winding are slowly and carefully unwinded to record down the original turns and taps location for rewinding later. Luckily the damage was not that bad that prevents us from doing so. If not, another unit might be needed to complete the big picture, or smart guesstimate based on physical unit + theoretical data will be required if no references are available.

Another challenge was presented to us when it is time to rewind it - the wires used are of diameter of 0.05 with 3000 rounds of primary turns with a center-tap!!! It is quite difficult to rewind and had to be manually done slowly. If it is broken, what's done will have to be thrown away and new one redone. 

After a 3 day affair, finally it is done! It will be shipped back for testing before another 3 remaining units are repaired with the same methodology & processes. 

Refurbishing or repairing input transformers will be worth doing so if it is those vintage exotic ones such as those Western Electric types where a pair could be U$1K - U$2K nowadays, or for those looking to restore expensive vintage equipment to original condition that can fetch pretty good price in the market.

J&K
9/9/2016

HIFI Ground Box Review

We've received another stunning review from notanotherhifiblog.blogspot.com! Click the link below to get to know more about it!

http://notanotherhifiblog.blogspot.sg/2016/08/grounding-for-better-j-audio-design-3io.html

Link to the ground box - 3io's BlackBox!

http://jandkaudiodesign.blogspot.com/2015/03/3ios-blackbox.html

This unique ground box is ONLY available at J&K Audio Design and not anywhere else in the whole world. It is made with unique passive electronic circuit that works indefinitely. It is not the mineral based grounding box that is flooding the market now with lots of clones from Hong Kong and China, which may or may not work. 

Enjoy!

Hear the Unheard!
J&K Audio Design
8/25/2016

3io Blackbox Review

Another stunning REAL user review from our audio transformer customer, not some paid write up or review! 

Usages
* Connect to phono ground 
* Connect to mains socket
* Connect to power conditioner
* Connect to power strip
* Connect to grounding post of equipment



3io's Blackbox

*** Start of review *** 

Hi, Ken and Jolin.

I'm angry. I like audiophile "accessories" as much as the next person. But when a manufacturer claims to "control a quantifiable amount of free electrons", my eyes glaze over. It's just this type of audiophile hyperbole that gives us all a bad name. Enter J&K's 3io BlackBox.

Let me offer a bit of background. I'm an electronics engineer by day and a hard-core DIY'er by night. I designed and built virtually all of my audio equipment myself. I have nearly 30 years of experience doing so. My system is vinyl-based, and all of my electronics use vacuum tubes with the occasional solid-state augmentation. My loudspeakers use pro drivers and a high-frequency horn.

I know the sound of my system quite well. Others have described it as big- and clear-sounding. It has slowly evolved over time to where it stands today. It is stable with no audio "surprises" when the music comes out. And music does indeed "come out", at least to these aging ears.

I recently had the opportunity to install a new phono cartridge, and I've been listening to it quite a bit. I felt that I had zeroed in on the characteristic sound of this cartridge, and I was pleased. I then received an email from J&K asking if I would like to audition the afore-mentioned 3io BlackBox, which was in the US for review. I know J&K make good stuff; I use and have heard several of their output transformers, so I know they can hear as well. Why not, I reasoned, setting aside my engineering sensibilities.

I figured the best place to start would be in my phono stage. I ran a clip-lead from the 3io BlackBox to the ground post on my phono preamp and sat down to listen. My mental notes go something like this:

"Hmm. The cartridge must still be breaking in. Sounds quite a bit nicer than last night."
"Gee, the bass has really tightened up!"
"Wow, listen to the separation of the instruments in the background!"
"It's like the singer took a step forward and the instruments in back spread out."

With trepidation, I started to wonder if the BlackBox had anything to do with it, so I disconnected it. It's as if a gentle haze had now settled in over the sound field, slightly but audibly affecting the overall system definition. Bass became a little "warmer" and things just seemed to get a bit more congested. "This can't be", I said to myself. I re-connected the BlackBox to the phono preamp, and the previous sense of clarity was restored.

I have confirmed to my own satisfaction that this 3io BlackBox has obvious benefits. Admittedly, its effect is pretty subtle, but not so subtle that it isn't plainly audible after a short period of relaxed listening. Its presence did not immediately announce itself; if it had, I would have been skeptical. I've learned that changes that jump out at you rarely prove to be improvements over the long term. It's the kind of change you'd hear moving from a $2000 phono cartridge to a $4000 one, and there are a lot of $2000 cartridges that I could live with. This 3io BlackBox brings the kind of improvement that I think most audiophiles and music lovers will appreciate.

No, it's not a magic clock or a fancy rock. Maybe there is benefit to harvesting all those free electrons polluting the grounds of my systems. But I'm mostly angry that my rational side doesn't understand the underlying technology. But at this price, who's complaining? I'm keeping the review sample.

Nice work, guys!

*** End of review ***

Hear the Unheard!
8/18/2016
J&K Audio Design

Audiophile DC Blocker Review

Nothing makes us happier to receive REAL user reviews for our DC blocker. 

The DC riding on his mains are giving him some issues and he requested for a pure DC blocker, without any noise filters and other functions with the DC blocker. The money saved are used to upgrade to better components for the DC blocker, and therefore better sound quality is achieved.

http://jandkaudiodesign.blogspot.my/2014/11/mains-dc-blocker.html

Hear the unheard.
8/8/2016