Hi Guys,
Impedance in electrical engineering terms refers to reactance, or the opposition to AC signals seen due to inductors (inhibit AC currents) and capacitors (inhibit AC voltages). The term impedance I think is used too casually. If there is just a resistor (what sets the input impedance of most amplifiers) and no reactance so to speak of, why is it called input impedance? Input impedance would be zero and resistance (not reactance) would be whatever that resistor is.
I start to become confused when transformers are introduced into the picture.
- DC resistance of transformer coils is very low so input impedance is clearly not DC resistance.
- Frequency response is flat from 20 to 20k and beyond in a good quality transformer so reactive impedance would be constant so to speak in the audible range.
- 600 ohms seems low for an impedance number, as most preamps have input impedances ranging from 20k and upwards.
A standard impedance ratio is 1:2. Lets say it is 600 ohms to 2400 ohms. How would you determine the input impedance to your amplifier if a transformer with a 600 ohm primary and 2400 ohm secondary is used? Would it be just 600 ohms?