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October 20, 2011


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Frank Walker

Interesting. What is the mechanism which causes this to be the case?

John Dunn

There is electrostatic coupling from a capacitor that gets placed on the "hot" end of the winding, especially if that capacitor is physically large such as a CS13-style part. In the case that led to this, there were over a dozen different audio signal paths, each of which (to simplify just a little bit) needed to be isolated from all of the others by 100 dB.

Marco Ramondetti

Sorry John but I don't understand why this electrostatic coupling happens only with the capacitor in high side position. Maybe because in low side one terminal is connected to ground?

John Dunn

Hello, Marcos. When the capacitor is put on the low side of the winding, one end of that capacitor is indeed at ground. Since the capacitor is a low impedance device, the ungrounded end is at ***signal*** ground as well. The high side of the transformer stil carries the full signal of course, but that lead can be given shielding. There was no way to have shielded the capacitor itself.

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