How do I determine the 'Z' of an Output Transformer (OT)

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Joined: 06/27/2008

The 'reflected impedance' of an output transformer is determined by calculating it's 'turns ratio'

To find the turns ratio one applies a known (low) voltage AC supply to the primary tap and measure the voltage seen at the secondary (speaker).

As an example if 20V AC is applied across the primary and the speaker tap gives 1V out the ratio is 20:1 ...

The reflected impedance is the speaker load times the ratio squared, so for an 8 ohm speaker and the above ratio:

8 x 20 x 20 = 3200 or 3.2K

If the speaker was 16 Ohms, the OT load would be 6.4K

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