C core output design

[audiophilediyer]

Hi cerrem,

Thank you for you help on designing my output trans. Everything is clear and detail.

Although DC resistance is quite high, I will wind a pair for my 6C45 amplifier and will let you know the result!

Thanks.

Regards,
BigBulb

 

[cerrem]

Yes...you are correct that the DC resistance is high....BUT this is because you are dealing with a core that is not optimum...
So you have trade-offs....I can lower the DC resistance at the cost of lossing bandwidth or increase in core distortion...
The DC resistance is actually the lesser of the 3 evils...
If you can...try to avoid KRAFT paper with varnish.... Use Kapton or Teflon sheet...and NO varnish....

Chris

 

[audiophilediyer]

Hi,

KRAFT paper with varnish will sound bad? Teflon sheet is good but might not fit into that window I think..


Regards,
BigBulb

 

[cerrem]

For Hi-End OPT's I never use KRAFT paper and varnish....since this equates to a dielectric constant of about 3.5 .....
Instead I cut up and use TEFLON or KAPTON sheet...this way the Constant is about 2 to 2.4......
This affects the winding capacitance....
It also depends on the design.....If the design already has low capacitance for the application, then I might go ahead with KRAFT and varnish.... WHen using KRAFT paper..it isn't electrically safe until it is vacuum impregnated with varnish then baked...
When using TEFLON or any of the styrene's ...then you don't need to varnish...just makes sure you wind it tight,..... A power transformer would be another situatin where you would need to varnish the winding or you will hear buzz...

Chris

 

[audiophilediyer]

Thanks for the explaination. If I didn't varnish it and just use teflon or stylene, the copper winding will vibrate whan the OPT is operating, the OPT will "sings" all the time even with only connected to resistive load. some of my friend says that the copper's vibration without varnish will induce slight back emf and create more harmonic distortion, don't know if it is true but for power trans I'm sure varnish is a must.
I had experienced of re-winding a power trans without varnish, and it buzz and burned after few days of operation due to the copper's vibration cuts the surface of isolating material of copper itself and short circuit....

Regards,
BigBulb

 

[Soundblaster]

I've found a good source of Teflon can be found in the plumbers section of the hardware store. Teflon Plumbers tape is cheap, thin and plentiful.