Output transformer preamp transformer

Thanks to one of our great and frequent customer, this article is born.

Before we start our lecture, take a look at this picture below of Tamura A-4714 signal transformer. Do you see any peculiarity about this Tamura A-4714 signal transformer? 

Sorry, right guess does not win any prizes here. LOL! 

Yes, it is an output transformer. Yes, it is a pre-out / pre-amp output transformer. What? Two types in one? Yes, two in one! 

Based on the limited information available, it is a signal transformer with primary of 5K that is capable of ~50mA of DC current, and a mixed secondary of 150 Ohm + 150 Ohm + 6 Ohm.  

1. Application 1 - use it as a power amplifier output transformer capable of ~3W output.
2. Application 2 - use it as a pre-amp output transformer with either 150 Ohm (secondaries in parallel) or 600 Ohm (secondaries in series) output impedance.
3. Application 3 - use the additional tap as a feedback tap to reduce distortion, as seen in some innovative designs in very old designs. It may be present in modern designs but I rarely see one. 
4. Application 4 - use both! 

How to design the circuit - hmm... maybe next time. There are plenty of sample circuits online. If you buy one from us, maybe I shall consider spending more time to teach you how to do so. 

Now this sort of signal transformer is kind of fun, right? If you're undecided if your tube is going to be used in either applications, order this transformer! You can decide later and still have the right transformer to use - now ain't that cool! 

Of course, buyers be warned - universal design is a compromise. A dedicated transformer will be better, minimalist, as we always preach. For the fun of it, I see why not. Also, the user said it is one of the good transformers he owns. So, I believe, we can do better than that! Challenge accepted! 

Good old used or NOS Tamura A-4714 could still be found occasionally in eB*y or all sorts of online sellers out there. If the A-4714 fits what you need, perfect. If you need something that is out of ordinary, custom made, then you know who to look for - J&K Audio Design! We can make it to any primary and secondary taps that you need. So far I've not seen new ones being made - I may be right for now, and wrong later. You can check Tamura website and see if it is there. 

The sky is the limit! Seriously. We can use almost ALL sorts of cores available in the world. And we have 3 types of magnet wires to choose from - ordinary John Doe OFC, to exotic OCC Copper and OCC Silver cable wounded output transformers. Oh ya, any voltage (as high as your dare) and any DC current for the primary too (1A? No issue, been there, done that!). 

So, for those under-decisive souls out there, your savior is here!

Do I have an actual picture of it? Nuh... it looks the same like every output transformers out there - bare naked or potted. They all looked the same. You want special casing? Hmm... maybe we can do so now - since we've found a LOVELY LOCAL vendor here. He's a bit busy though - so expect longer lead time if you need a fancy output transformer case. 

Meanwhile, take care and stay away from being infected with COVID-19. Stay safe at home. DIY more audio amplifiers. Buy more transformers from us!

J&K Audio Design
22/6/2020 

Shunt Reactor

People has been talking about the evil artifacts, such as, noises the active regulation brings, for example, those using a toroidal transformer with a motorized carbon brush, or even relays to switch to multiple taps in the transformer, to adjust the voltage when there are elevated mains voltage or brown-outs. Or, some audiophile just despises in-line or in-series regulators, saying that they choke the sound of their system, or restricts the dynamics  

So, is there a more elegant way of regulation other than the active way? Is there a way to regulate with passive components? Is there a shunt type of regulation device that can help with regulation? When it comes to transformer, or anything with a core and wire, ask us! 

Well, there is! And, it is called Shunt Reactor! 

Shunt reactor is used in industrial applications, more than home environment, where it is an absorber of reactive power to increase the efficiency of energy transmission, or to compensate (or consume) the reactive power generated by capacitive loads line capacitance - Ferranti effect). 

An inductive load consumes reactive power. A capacitive load generates reactive power. We have too MANY capacitive loads connected to our power line right now, especially with high power amplifiers that uses a lot of capacitors. Even an OPEN POWER LINE generates reactive power. 

The shunt reactor is normally connected permanently to the power line, or sometimes are switchable, or adjustable (VSR - variable shunt reactor) to cater for different daily-hour power draws or seasonal dips and peaks of power draw. 

In layman terms, shunt reactor automatically stabilize the voltage levels. minimize over-voltages. 

Usually the shunt reactor is permanently connected, or switched by a circuit-breaker (circuit-break is required ***important***). Several shunt reactors with different can be connected in parallel, or switched in and out to adapt to different power line conditions. 

A simple connection diagram of the shunt reactor is as above - across the live and neutral lines. For balance power, you will need two units of them to work in tandem. 

WARNING: It is dangerous and LETHAL mains / live AC voltages you are working on. Do it at your own risk. It is for qualified electrician only. WARNING. 

What consists of a good shunt reactor design? 

• Air-gapped core - constant impedance, reduce loss, avoid saturation, promotes linear energizing, and minimize remanent flux in the core (flatter hysteresis B-H curve, lower inrush current) 
• High inductance - high energy storage and resistance to changes 
• Low DCR or thick wire gauge - quick charge and discharge
• High grade core - minimize power loss, lower vibration and noise  

A shunt reactor may look like a transformer, but it is intended to consume or compensate reactive power, where as transformer is to convert one voltage to another, or one impedance to another. Shunt reactor has only one winding. Transformer has 2, and above for the conversion. 

Since it is switched on all the time, losses becomes important to avoid high electricity bill and heat. What are the major losses in a shunt reactor?

• Copper losses in the winding - wire 
• Core loss - iron core loss 
• Eddy current losses

Therefore, it is critical to minimize losses, and have a good shunt reactor design for better reactive power compensation / voltage regulation. 

Now, are you ready to DIY a shunt reactor device and use it in your home environment? 

J&K Audio Design
2/5/2020 

Value for money output transformers

Best bang of the buck output transformers! Value for money output transformers! Good sounding output transformers! Good things need to repeat 3 times!

Hope everyone is well in terms of the COVID-19 outbreak, as well as the current stock market correction period. In such treacherous period of time, what’s better than staying home and do some self-improvement reading, market research/analysis and new product design!?!?

Who’d like to have a best bang of the buck output transformer? Please raise your hand! We’ve surveyed the market of output transformer makers, list out some of the popular names such as Lundahl, Tango, Hammond and etc to analyse what’s good, and what’s to be had.

The picture shows our rating based on our own criteria – take it with a cup of salt.

What are the critical parameter for output transformer?

1. Primary impedance ~2.5K to 3.5K (common impedance for most tubes)
2. Primary DC 100mA at minimum (suitable for 2A3, 300B, KT88, KT100, KT120 till KT150)
3. Primary inductance of ~6H per 1K Ohm (for better low frequency loading/response)
4. Secondary 0 – 4 – 8 Ohm (suits most speakers out there)
5. Output power 30W (decent, but not too low)
6. Frequency response of at least <20Hz and > 20kHz (for full HIFI bandwidth)
7. Tolerance of +/-1dB (where human ears could hardy differentiate a 1dB difference)
8. Decent headroom/core volume >= 1KG per 10W SE
9. Decent price <$150/pc

With all the above criteria in consideration, we have come up with 2 output transformer designs to satisfy most users needs. We cannot do an All-In-One output transformer as the design trade-off is just too much.

Therefore, one (JK Fighter P-OPT) is designed more for Pentode (KT88, EL34, EL84, KT120, KT150, and etc).

• Higher primary inductance to cater for higher tube Rp (Pentodes in general)

The other (JK Fighter T-OPT) is designed more for Triode (50, 300B, 2A3, 45, 71, R120, 300BXLS, PX4, and etc).

• Lower primary inductance to cater for lower tube Rp (genuine Triodes in general)
• Additional 16 Ohm secondary for high efficiency speakers  

For those that wish for a warmer sound, they can use JK Fighter P-OPT with Triodes or even Pentodes. For those that want a more high fidelity sound, JK Fighter T-OPT is the one to go.

Expected availability ~June 2020. If you’ve feedback on the design for improvements, or you happen to be looking for one for your design(s) – let us know before we finalize the design. Email us! If they are valid and genuine, and doable within the budget, we will include them.

To keep the price low, they are all fixed design. If you need to customize, it will have to be on standard customize price. Custom made version will be more expensive, and will have better dynamic headroom too.

We have no plans to release Push-Pull versions since those have lower demand. If there are a lot of queries, or even OEM requests, we may consider doing so – let us know.  

Thank you for your support!

Take care everyone! 

J&K Audio Design

28/2/2020

tweeter attenuator transformer

Mids highs attenuator transformer - useful tool for final tuning of mids and tweeter to match listening room conditions, seating distance, and woofer / mids / highs volume level. It can be useful during crossover design phase too, to try with different attenuator taps / levels before deciding on the final attenuation levels. 

For those speakers with bi-wire or tri-wire connections, one can even use this to attenuate or boost the mids and highs if one feels that the highs / mids / bass levels are mismatched with their listening room or listening taste. 

100W Transformer Attenuator

Tweeter attenuator transformer

Attenuator / booster transformer

Tango has made some in the past, model Tango SA-300. 

For ours, we can custom it from 30W to 300W, or even 1KW if required. Pictured above are the 100W version, with total DCR of about 4 Ohm end-to-end, 11-steps at 2dB per step. Other configurations can be made per customer requirements. 

Users can choose the output format (potted, bare frame, stand), cores (Hi-B, Amorphous, Permalloy, NanoCrystalline), wires (OFC, OCC Cu, OCC Ag), taps (10-step to 33-step), power (10W - 1KW), and anything that the user needs.

Applications #1 - attenuate
- connect two ends to amplifier output
- connect the middle steps and return step to the mid/tweeter
- choose the steps to select attenuation levels

Applications #2 - boost 
- connect mid step and return to amplifier output
- connect the higher steps and return step to the mid/tweeter 

- choose the steps to select boost levels

Reference prices for mid/tweeter attenuator transformer: 

30W version
- OFC - U$150/pc 
- OCC Ag - U$490/pc
- OCC Cu - U$260/pc
- Amorphous / Permalloy / NanoC core upgrade +U$50/pc
- other parameters, please email

100W version
- OFC - U$260/pc
- bare frame 
- other versions, please email

* 10 step at 2dB/step (other steps quantity and step size can be made) 
* Potting adds U$30/pc.
* 200Hz and above (mid-high use only)
* Full frequency range unit can be made too 

For bare version, we can only use OFC magnet wire with adhesive property to ensure the wires stay aligned and together during and after winding. For other type of wire, those without adhesive properties, they need to be potted to ensure the coils do not move around. 

For full range version, also known as unity-coupled-transformer, it can be made too. These transformers are used for speaker impedance matching purposes, as well as to gain some "tube sound" by using it as "output transformer" in solid state amplifiers. 

One can connect the amplifier to the 8 Ohm tap, and the right output impedance is chosen to match the speaker impedance. These are useful to drive low impedance speakers, or difficult speakers that have huge dips in the impedance. Or, if one is using 16 Ohm or 4 Ohm speakers, and only have 8 Ohm output tap at the output transformer, they can connect the amplifier to 8 Ohm tap, and use the 16 Ohm or 4 Ohm tap to connect to the speakers.

Tips:
1. If attenuation can be done earlier at the signal chain, do it earlier, such as attenuate the signal at the source (DAC output) rather than at the destination (amplifier output). In such application, TVC (transformer volume control) can be used. 
2. Transformer coupling is better sounding that Autoformer coupling (our findings), YMMV though. Experiment and find out yourself which is better in your application or taste. 
3. Fixed attenuation with single tap will be better than multi-tapped autoformer/transformer. Simpler is better - this rule does not change. Multi-tapped autoformer/transformer offers the flexibility for tuning or matching on-the-fly. This will be good during designing, experimenting, or tuning phase, or even for users that try to tune the system for different type of music / speakers / rooms / taste. Single tap transformer/autoformer could not be as flexible. 


J&K Audio Design
9/28/2019

Super Hi-B EI Output Transformers

Good day folks! We have been quite quiet these days on the blog, but we aren’t dead!

Things are moving at a very fast pace at the background to fulfil all the orders. Apologies if your orders take such a long time. Lead time is long to maintain the quality of the products. If you are in a rush, please submit your orders early, or go somewhere else please if you’d like to rush things. I’m sorry we cannot take rushed orders. Thank you for your patience in advance, and your support all these years. We cannot make it that far without all your love and blessings on our products!

For those that prefers more frequent updates, they can visit our Facebook page where we frequently post about our product news, and interesting HIFI related topics. We welcome your emails to discuss about anything related to HIFI or audio transformers with us. We are open to partnerships or ODM for your equipment needs. Just drop us a mail.

For this round, we would like to introduce you guys to our Super Hi-B EI core. I believe all would be familiar with the EI Z11 core used all over our standard offerings, which is considered quite high quality compared to the lower H cores used elsewhere. The Super Hi-B EI core is even better.

The Super Hi-B EI core have higher permeability and lower core loss (~35% lower than EI Z11). Super Hi-B EI core loss is only ~0.92W/KG (versus ~1.25W/KG for EI Z11)! We have been experimenting on using this core on the most commonly used 300B output transformer and got excellent results. Based on all similar design parameters, with just the difference on the core material, Super Hi-B EI versus EI Z11, the Super Hi-B EI core boasts 20% higher primary inductance compared to EI Z11. This has opened a door for a better output transformer design!

With the lower core loss and higher inductance generated with the Super Hi-B EI core, we can notice obvious improvement on the output transformers. The low frequency, in terms of linearity, extension and quantity, are so much better with the Super Hi-B EI core compared to EI Z11 version. The control and grip on the speakers are much stronger, and therefore you can “feel” that the power is higher. There are some improvement on clarity and transparency too, possibly due to the lower loss of the core, and the different design approach we take for this core since consideration or compensation for higher primary inductance is lesser in some degree.

A lot of tube amplifier users feel that the low frequency fidelity for tubes are not good and deep enough. They should try to listen to this version with Super Hi-B EI core. We can easily get low frequency response of 10Hz @-1dB, and more if the users have special request.

The EI core size profile is quite complete for this Super Hi-B EI core compared to the C core version that is limited in sizes, and therefore there are more flexibility in terms of the VA or capacity, and the ease of more deeper customizations. Super Hi-B EI core has size of EI 66, 76, 86, 96, 105, 114 and 133.

And yes, to answer some extreme customers, that these cores can be used as power transformers or chokes too. And yes again too, for even more exotic users, we can pair this with OCC Copper or OCC Silver wires, to make the ultimate output transformer for your project.

Send in your orders now, and be amazed with the renewed life of your tube amplifiers! Apologies on all words article – the EI core all looks the same. There is nothing much to see, but it is much to hear!

J&K Audio Design

27/7/2018

Fully Built Transformer Volume Control

Fully Built Transformer Volume Control - would anyone be interested?

We REALLY hesitated on introducing a fully built transformer volume control due to the amount of manual labor required to solder the TVC to the step-switch. One unit of fully built stereo Transformer Volume Control takes 5-8 hours to solder!

Due to the overwhelming response from readers asking for a fully built TVC as not many are trained on soldering and building audio kits, we are introducing this, for a limited time, for a limited quantity, for batches order only so that we can keep the quality in control. 

Also, we think that Transformer Volume Control is something that an audiophile must own as the improvement in sound is just substantial over the price paid (very high cost / performance ratio), we are doing a limited time promotion on standard configuration standard TVC to keep the cost of making them down. 

Standard standalone 24-step TVC - U$590/pair (RM-2350) (special batch order price only)
* 24-step, potted with turrets
* Hi-B core only (others - will be normal price) 
* Primary 600 Ohm, secondary: 600 Ohm

Note: It will be built in a batch of >=5 sets. You can order 5 sets or more, or wait for 5 sets to be accumulated before build starts. If you order >=5 sets, you can customize it slightly, please email for details.

Fully built stereo unit - U$990/unit (RM-3950) (special batch order price only) 
* built with standard 24-step TVC above
* full aluminum chassis
* 24 step attenuator switch 
* double-screw chassis 
* input grounded, or output grounded, or floating (need to ground at chassis)
* single set of stereo input and stereo output

Note: It will be built in a batch of >=5 sets. You can order 5 sets or more, or wait for 5 sets to be accumulated before build starts. If you order >=5 sets, you can customize the parts used (some at extra cost), please email for details.

Sample fully built TVC is as follow: 
* outlook and materials may change depending on parts availability

TVC - fully built

23 step TVC only (shown is 33-step as sample only)

Silver Plated OFC wiring

33-step version shown as sample only

Made in Taiwan 24-step switch

What's the difference between this and the custom made version? Custom made (more expensive) version offers superior cores - NanoCrystalline (aka Finemet), Permalloy and Amorphous, and is customisable (different primary/secondary impedance, different step-up/down ratios, configurable and etc), different grade of wires, solder, and etc. Sound quality wise, custom made version is a grade higher too (that justifies the price!). 

Still, this standard version is excellent sounding - with extended frequency range, solid vocals/body and clarity! The difference between TVC and resistive stepped attenuator is easily differentiated even by non-audiophiles! You owe yourself to own it, trust us!

Till then, grab hold of this opportunity to get yourself a fully built TVC, or a raw Transformer Volume Control, for your long awaited birthday present, Christmas present, 1st draw pay gift to yourself, wedding anniversary present, and(or whatever reasons you can cook up)!  

While it lasts... don't regret after promotion is over, or before we regret it.

J&K Audio Design
4/21/2018

OCC Transformers

Greetings J&K followers! 

Apologies for not posting for some time. Busy, busy, and busy... that's what's left in our life! 

We didn't intend to post but we can't resist to do so since we have to take some pictures for one of our customers locally. He had ordered a set of unique transformers for his preamp - OCC copper power transformers, OCC copper filament transformers, and OCC copper chokes! 

We have always been a producer of high quality transformers. We can't resist the opportunity to promote OCC based transformers! Most of the time, OCC are used only in speaker cables, interconnects and power cords, but why not transformers? 

For us, OCC output transformers are quite common. OCC power transformers and chokes are rare, although not uncommon actually. We've made quite a lot of OCC ultra isolation transformers and output transformers for a few customers based in U.S.A. 

What are the benefits of OCC based transformers? From electrical properties perspective, they have lower DCR compared to standard magnet wires - lower impedance. The insulation paint is a few magnitude better than the standard ones too - longer life! 

Based on our listening tests, and feedback from customers, are that OCC copper transformers have smoother highs, more extended in mid-low bass and more refined in mids + highs. In overall, they are well worth the money spent compared to spending them on power cords, interconnects or speaker cables IMHO. The length used in transformers alone would explain why the differences are more significant compared to exterior cables. If you are already using OCC cables, investing in OCC transformers are a must in order to fully exploit the goodness of OCC wires.

Post-script: We are starting to explore OCC silver cables. We have limited stock of OCC silver wires ordered for a customer. There should be some leftover that can be used for a limited range of transformers. For those that could not fit what we have, we are very sorry that we still need some time to stock up more OCC silver wires (raw OCC silver wires are ultra expensive. The finished OCC silver transformers will be pricey.). If you are interested in OCC silver wires made transformers, drop us a mail and we shall see if something can be made just for you. 

Till then!

We wish you a very Merry Christmas, and a Happy New Year! 

J&K Audio Design
12/20/2017

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:

http://jandkaudiodesign.blogspot.my/2014/02/quad-c-core-output-transformer.html
http://jandkaudiodesign.blogspot.my/2014/03/c-core-output-transformer.html

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.

http://jandkaudiodesign.blogspot.my/2016/06/high-power-pp-output-transformer.html
http://jandkaudiodesign.blogspot.my/2016/06/high-power-se-output-transformer.html
http://jandkaudiodesign.blogspot.my/2016/05/coupling-transformer-interstage.html
http://jandkaudiodesign.blogspot.my/2016/05/level-2-push-pull-opt.html
http://jandkaudiodesign.blogspot.my/2016/05/level-2-single-ended-opt.html

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
10/21/2017

Tamura STU-001 Input Transformer

Tamura STU-001 Input Transformer

Tamura Input Transformer - STU-001, 150,300: 100KCT (Push PULL). Tamura STU-001 is widely used in designs by Sakuma-san, in Sunaudio amplifiers, and designs in MJ Audio Technology magazine. 

Unfortunately, STU-001 input transformers are out-of-production now(at time of publication), and is quite rare to be found now. We've received quite a lot of inquiries on similar high step-up ratio input transformer such as the Tamura STU-001 and have decided to open it up for mass market instead of making them quietly in the background. 

Below are some applications designed and built by HIFI enthusiasts from the East. It can be used as single ended step-up, or phase splitting for push-pull use. You will also notice that directly after the Tamura STU-001 input transformer, is power tubes, such as 211, or 300B, meaning that it is some sort of a Supercharger amplifier, or power amplifier. 

We have blogged about supercharger amplifier in the past - you can refer to this post:
http://jandkaudiodesign.blogspot.my/2016/01/supercharger-amplifier.html

 Applications

- transformer is a ratio machines, with such high step-up ratio, the secondary load needs to be very high impedance, and the primary source needs to be very low impedance, to keep the bandwidth wide enough for audio applications
- 300:100,000 equals a step-up ratio of 1:18, or impedance ratio of 1:333. Load will be reflected accordingly to the primary and the source will need significant drive strength to ensure satisfactory performance
- volume pot is not recommended at the primary of such input transformers for higher fidelity

Let's take 250K and 500K (maximum grid resistance 300B and 211 can tolerate in self-bias circuit, fixed bias will be much lower) secondary load for STU-001 as example.

- primary reflected impedance = 500K / 333 = 1.5K Ohm 
- primary reflected impedance = 250K / 333 = 750 Ohm

You can see that it is not a really friendly load for weak (high output impedance) tube preamplifiers. Most common-cathode topology simple tube preamps will not apply since the output impedance will be high. We would need tube preamps with low output impedance, such as those with Cathode Follower output stage to drive such STU-001 input transformers satisfactorily. Or, tube preamps with output transformers, that has low secondary impedance, such as 50-100 Ohm, or maybe lower, will work nicely. That reminds us of tube headphone amplifiers!

On the other hand, high swing low output impedance solid state preamplifier will come in nicely here. Therefore, choices are plenty. 

In some cases, secondary load may not be required, if there are no oscillations / overshoot or undershoot at the output of STU-001, and therefore, the secondary of STU-001 acts as a grid-choke for the driven tubes! 

One may asks, so what's the benefit of doing so? You can set the power tube free from the coloration of the driving stage! You get to hear the real sound, real character, true flavor of the power tube with such high gain input transformers. Imagine if the power tubes are WE WE 300B, 242, WE 211, WE 212, GEC & Telefunken power tubes and various other exotic power tubes. Such input input transformers such as Tamura STU-001 and the likes will come in very handy.

Note: Standard STU-001 may not have that much swing for high power tubes. STU-001 with larger cores (diff price) is needed for big power tubes. 


Hear the unheard! Sail the uncharted! 
Long live custom made audio! 

J&K Audio Design
9/21/2017

Autoformer Volume Control

Autoformer Volume Control, or Transformer Volume Control

We think that AVC, or TVC are one of the many great things that happened in audio industry in the past 10 years. The sound signature brought forward by AVC, or TVC can be stated as - better fluidity, warmer, wider bandwidth, and more analogous.  

For those that are unaware (not following us on Facebook, it is a good time to do so now!), we've found a new casing to house our TVC (Transformer Volume Control), or AVC (Autoformer Volume Control). 

Here are some pictures of the casing. The matte version is still available if one still want those. 

Some past articles on TVC and AVC. We can do both, but TVC is preferred due to various reasons, but we can still do AVC if customer prefers AVC. There's no right or wrong in audio, just what one prefers. 

Our preference:

** brushed pot -> stepped attenuator -> digital volume control -> AVC -> TVC 

http://jandkaudiodesign.blogspot.my/2016/10/transformer-volume-control-tvc.html
http://jandkaudiodesign.blogspot.my/2016/12/transformer-volume-control-review.html
http://jandkaudiodesign.blogspot.my/2017/04/j-transformer-volume-control.html
http://jandkaudiodesign.blogspot.my/2014/06/autoformer-volume-control.html

Some tips on using TVC / AVC: 
* low output impedance source is preferred but not 
* use a very high quality switch - it make or breaks the AVC / TVC
* durability of the switch is very important - you will be switching them quite frequently
* encased / sealed switch is preferred over open casing type
* step down type of TVC will have lower output impedance and will be capable of driving heavier loads compared to AVC 
* invest on good low melting point solder and good soldering irons - very swift soldering, with low melting point solder is preferred - TVC / AVC are made with very thin wires and are very fragile 

Hear the unheard! Sail the uncharted! 
Long live custom made audio! 

J&K Audio Design
9/19/2017

DAC output transformer

We have got a few requests to custom make DAC for a few customers locally, and have been researching on how to make a better output stage for I/V conversion for DAC chips with current output, especially differential types. 

We've tried many types, such as Op-amp, discrete, passive resistor, and transformer based. So far passive resistor and transformer based are our favorite. Both these give the most natural and organic sound. 

We've done some Googling, and we found that we're not alone! A few very famous modders (Lampizator) and custom builders (Andrea, and etc) have been promoting DAC output stage with resistors and transformers! 

It just so happen that we do have some ready made input transformers made previously for preamp input coupling / isolation use. It can be used perfectly as DAC output stage.

DAC input transformer

  600 Ohm : 600 Ohm DAC output transformer

• Permalloy EI core, with a small % of Z11 for voicing / sound tuning
• Core size: EI 35 
• Size: 66mm x 3mm x 33mm H 
• Signal level: 3 Vrms @ 20Hz 
• 20Hz -0.1dB to 100kHz -1dB
• Usages
•  DAC output, CD output, Op-amp preamp output, signal coupling (input transformer, output transformer), output inversion use
• Price: U$150 / pair 
• Limited quantity only, left over from mass production for a high volume manufacturer
• 5：1， 10：1 versions may be available, please email 

The simplicity of having transformer as DAC output stage is also something we liked!

 

This is as simple as it gets, and results are extraordinary!

J&K Audio Design

5/7/2017