AI Tutor
Plug a vintage ribbon microphone into a live console channel with phantom power engaged, and you might hear a sickening 'pop' right before the ultra-thin aluminum foil tears itself apart.
Yet modern active ribbon microphones actually require that exact same +48V supply to work at all. Why does phantom power destroy one design while powering the other?

The Passive Ribbon Motor

A standard passive ribbon microphone contains no active electronics or amplifier circuits. Sound waves move an ultra-thin corrugated aluminum strip suspended inside a strong permanent magnetic field.
Because the aluminum ribbon is so small and light, its native electrical resistance is minuscule β€” often less than 0.2 ohms (0.2 Ω0.2\,\Omega) β€” producing an output signal of only a few microvolts.
To bring this tiny signal up to standard mic level, every passive ribbon requires an internal step-up transformer.
How does boosting the voltage with a transformer affect the microphone's output impedance? The answer comes from transformer physics.

Transformer Ratios and Output Impedance

A transformer steps up voltage proportional to its turns ratio, N=Ns/NpN = N_s / N_p, where NsN_s is the secondary turns and NpN_p is the primary turns. However, power must be conserved (VpIp=VsIsV_p I_p = V_s I_s), which means current is stepped down by the exact same ratio NN.
Because electrical impedance is the ratio of voltage to current (Z=V/IZ = V / I), stepping voltage up by NN while stepping current down by NN multiplies the source impedance by the square of the turns ratio: Zout=N2Γ—ZribbonZ_{out} = N^2 \times Z_{ribbon}
Let's calculate the output impedance of a classic passive ribbon with a ribbon resistance of 0.2 Ω0.2\,\Omega and a 1:301:30 step-up transformer ratio (N=30N = 30).