I have headphones with differential input and impedance of 8 ohms. I need to drive this headphone with some DAC with built in headphone driver (Currently I have chosen ADAU1772). DAC's datasheet mentions that the minimum impedance of headphones it supports is 16 ohms. Can I increase impedance of my headphones so that I can drive them through this chip? What will happen if I drive this 8 ohm headphone through a chip supporting minimum impedance of 16 Ohms?
You have several choices:
- Get a chip that can drive 8 Ω.
- Put a buffer between the D/A and the headphones. This buffer must then be able to drive a 8 Ω load. The D/A only sees the input impedance of the buffer.
- Use headphones with 16 Ω or more impdance.
- Put a 1.4:1 audio transformer between the D/A and the headphones. The D/A output will need to be 1.4x larger than before, but will see a 16 Ω load when 8 Ω headphones are connect to the output of the transformer.
Nominal 8 Ohms for headphones is not much, and will make the DAC deliver the double current (compared to nominal 16 ohms).
You can not do much about it, as the impedance of the headphones are from the coil. If the impedance of the headphones were only a resistance, you could put a resistor in series (with power loss), but as the impedance is very frequency dependent, you will ruin the frequency responce.
I connected the speaker with 8 ohms resistors in series between headphones differential wires and dac output. I was getting a hear able sound. I removed resistors and connected the headphones directly, the voice got louder. However my application was outputting only male voice and no music. Dac was also not heating up while headphones were directly connected.