# Tranny CT scheme?

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#### Altaic

I'm making my own toroidal transformers from inductors I got for free from Wilco (www.wilcocorp.com). The ITL100 and ITL250 are recommended for making trannies. Free shipping... You can get up to five samples of each product, conceivably ~500 inductors per "sample kit." =)

Anyway, back to my question--
Is it better to physically center tap the tranny, or create a virtual ground using a couple caps and resistors? It can be buffered, too; check out http://sound.westhost.com/project43.htm for more info. I'm worried about the voltage of each rail to ground being slightly different. Should I be? The virtual ground guarantees equal voltage...

Will

#### Circlotron

Bifilar secondaries

If you wind your two half-secondaries in bifilar fashion, then you can bet your life they will be equal voltage if they have equal loads. If you twist the two wires together along their length before you wind them this will be even more so, but it will take up more winding space.

GP.

#### jackinnj

It get's a little bit more complicated, however. In simple terms, the impedance of the primary windings has to be high enough so that current, at 60Hz isn't too high, blowing the windings off. On the other hand, the impedance can't be that high that you are driving a coil with high DC resistance. I am sure that the engineers out there know all the linear programming tricks to calculate the optimal impedance. <p> The inductance of an 80 V.A. torroid transformer I just measured was 0.82 Henries. Calculate the reactance! If the core you just obtained from Wilco was only 10uH, you are going to need an awful lot of turns if you intend to operate it from the line. If, on the other hand, you are going to use it in a switching power supply at 40kHz it's an entirely different matter.

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