OPT with power transfrormer core

[fchouza]

Im trying to design an OPT transformer for a SE EL84 amplifier. Is possible use standard power transformers EI lamination (non Grain Oriented) for this transformer? Im using the Yves soft for OPT calculation with the Standard material selected, this is ok?. Sorry for my english!

[ray_moth]

No, for two reasons:

1. An SE output transformer has to have an air gap in the core so that it won't be saturated by the DC current through the primary;

2. The transformer needs to be designed for the full range of the audible spectrum, and an E-I power transformer will not fulfil that requirement.

[Sheldon]

Ray, I think he's asking if he can use power transformer laminations to build an OPT.

Yes, they can be used. But I think non oriented laminations will be a little less efficient, so a little larger core might be required.

Sheldon

[HollowState]

If you use ordinary power transformer steel, it will work but you will not get the best quality sound. I think most power transformers use a lower quality steel them M6 which is the generally acceped standard for outputs. Also, the laminations are usually a little thicker with lower permeability which adds to the decreased sound quality.

With this steel you should expect a lower level of detail (efficiency) and a reduced high frequency response. And of course, for single ended, you will have to restack the E & I lams together to produce an air gap between them. And you will have to experiment with the gap size as well. Good luck. You'll need it, CAD or not.

[aardvarkash10]

that core laminations are avaiable and cheap. Build a physically larger unit than you would normally and a lot of the disadvantages can be overcome. And what have you got to lose? I can buy complete 100mm cube PTXs surplus here in NZ for $5.00NZ - thats around $3.00US. A little work and some copper wire and I get experience and a workable OPT. It may not reach 40khz, but neither do my ears...

[tubesteve]

EI cores are used for SE Audio: but, all the "i" must be on one (the same) side, and insulated to the "E" side in order to create an "air gap". this air gap size is depending on the current thru the transformer, and for small SE power likely a bit smaller than 1mm. A piece of folded paper may do the job. check this with a caliper. All this is, to avoid saturation of the core, which would give you less power and more distortion

Cheap mains tranformers perform very bad at low frequencies, they improve a bit are at some KHz.
Strange: why we are using 50 or 60 Hz in the mains voltage then ?....

For audio the better grade is the "Z11" material. This is widely used by most manufacturers.
Most sheets are 0.35mm.

[fchouza]

Yes, the question is about use power transformer laminations, not the power transformer. What about the corrections in the soft or the calculations? Simply a larger core?

Thanks to all!