Check back regularly or subscribe for updates. Email us at jnkaudiodesign@gmail.com, or fill in the form on the left.

Saturday, December 21, 2013

Output Transformer Design



Output Transformer Design

Output transformer design requires a book on this topic alone. It sounds simple but it actually requires a lot of design considerations to have an output transformer design that meets its application. One cannot have an output transformer design that can do everything. That simply defies the law of physics. You cannot have everything in output transformer design.

One thing that really misleads users out there is the use of core types & materials, like C-core, double C-core, R-core, amorphous core, nickel core, cobalt core, silver wire, gold wire, 6N or more N wires and such. Yes, they make a difference, but if the techniques to properly utilize their unique characteristics are not there, we might as well go back to EI core which could be better if properly designed and implemented. It’s just a waste of materials. 

We really got to match materials with proper technique and application, only that will bring out the best from them. Over the years, I’ve tested lots of output transformers and some are really just marketing gimmick and nothing to shout about in quality. 

Let’s discuss some aspects of output transformer design.

The core size, core thickness, number of windings, wire size, and etc determines the output power of the output transformer. Having the right size will greatly affect the quality of the output transformer. We need to choose the right core size and thickness, matching the number of windings and wire thickness to obtain the right output power capacity. The low frequency response especially, will rely on this. If the core size is too small, the output will be distorted and bass will be thin, worse if it is working at rated power. 

Forever increase of core size will not solve everything as well. Having a larger core also signifies that the wires need to be lengthened as the winding diameter increases with the size. Wire length increase will raise the wire resistance and therefore creates additional voltage drop, meaning more wire loss. It will also increase the windings surface area and therefore increase the winding capacitance, causing poor high frequency response. 

To counter wire resistance effect, wire gauge needs to be increased. Increasing the size caused the space available to be lesser for windings and therefore the core size need to be increased to fit in enough windings to get the right ratio. This process goes on. 

Other than the above, the kinds of magnet wires being used will also affect the output transformer design. If one just look at the core gauges for design, they the results will be very disappointing as one fails to consider the insulation of the magnet wires (enamel) that will cause difference frequency response and impedance change. Different thickness of the insulation/enamel will generate different winding thickness and therefore varies the coupling between the winding, for good or for bad, and that, needs to be taken into consideration too.

What about the insulator layers in between the windings (if one does use it of course!). To us, it is very important for the safety + reliability perspectives and we manage to make it as transparent as possible. Not having insulator layers will greatly reduce the lifespan of the transformer if not done correctly. As previously blogged, different insulation materials have different electrical characteristics. That will directly affect the frequency response and coupling between layers. Too thin, is not good, too thick, is not good as well. Better insulation material increases the magnetic coupling and therefore increased the high frequency response, but that’s not always desirable to get balanced frequency response. 

Then, here comes the impregnation medium, varnish, lacquer, wax, compound mixture and etc. All these will again change the already so complex equation.  

You want more? Okay, let’s assume materials are all settled. Now we need to focus on the primary inductance. Output transformer low frequency response depends on having adequate primary inductance. Higher inductance equals to higher number of turns. Higher of turns also equals to lower high frequency response, and vice versa. So, we need to go back to the drawing board to ensure we have flat low to high frequency response. Panting now? 

We’re not done yet! Let’s get back to the core material. Some will always like to have amorphous, nickel or cobalt core as their output transformer core material. Well, all of them should be better as they’ve better permeability ratio, which gives higher efficiency and better high frequency sensitivity. Well, there is no perfect material in this world. Higher permeability comes with lower flux density compared to Z11 iron core, almost 30% or less. So to get the same output power, one needs more core material to gain enough low frequency response. There goes again to the wire size and surface problem. So, sometimes we’d prefer to gain the advantage of special core materials although still having the Z11 core by special winding techniques and experience. This is much easier to be achieved.

Of course, we’re not against such materials but we’d like to alert the users that all these considerations need to be taken before you order your output transformer. For such core materials, be prepared to pay more for the increase in size and sometimes due to law of physics, you got to lose some to gain some others. There is no free lunch! Don’t be fooled if someone says you can have it all, you can’t!  

So, balancing all the aspects is crucial to achieve excellent, not just good transformer design. Also, part of it will require trial and error to get to a certain understanding and mastering of output transformer design. Everyone can wind a transformer, but to wind a good transformer, not everyone can manage it. 

J&K Audio Design
21/12/2013


Product Lists  

Level 0

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.

Search This Blog

Product Lists

Product Lists

Level 0: link 1

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.

Follow by Email

Follow us using Google+ Badge to get instant updates!

Google+ Followers