OT primary · speaker load

Output Transformer Impedance Calculator

Match your output transformer's primary impedance to your speaker load correctly.

Bench tool

Work out reflected primary impedance from a turns ratio, or derive the ratio itself from a measured AC injection test.

Transformers
Match your load correctly. A good tech trusts their ears, but a great tech backs it up with hard math — get your primary impedance right before you let the magic smoke out of your iron.

Don’t know your turns ratio? Inject a low AC voltage across the primary and secondary and enter both readings below — the ratio fills in automatically.

— Ω PRIMARY IMPEDANCE

Enter a turns ratio and a speaker load above.

All secondary taps at this ratio

2Ω

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4Ω

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8Ω

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16Ω

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Impedance ratio (N²)

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Reflected primary impedance follows Zp = N² × Zout, where N is the primary-to-secondary turns ratio — not the impedance ratio some datasheets list instead. If you inject a voltage instead of using the nameplate ratio, N is simply Vp / Vs, since voltage is proportional to turns in an ideal transformer.