CurtPalme.com Home Theater Forum

[Maria]

Hello experts,

Need help designing headphone amplifier circuit -

I have to design a headphone amplifier circuit. We are told the impedance of the headphones and the minimum voltage they require and also the voltage source. After researching I have found that the LM386N-4 is a popular choice. (an example from datasheet LM386N-4 - https://www.icrfq.com/part/2377557-LM386N_4.html ). I've seen many circuit diagrams but what I don't understand is how to pick the voltage gain needed for the amplifier.

I originally thought that you would need to know the input audio signal voltage and when you multiplied that by the gain that would need to give the minimum voltage required by the headphones, but it appears that what matters is the current which I don't get.

And are you able to design such a circuit without knowing about the audio input signal? If you do need to know about it what is it you need to know about it and why?

I would greatly appreciate any help as I am very lost.
Thanks in advance.

[cmjohnson]

The industry standard for line level audio which your amplifier will be fed is 2.83 volts peak to peak, or 1 volt RMS. That's a 0dBfs (full scale) signal.

That may be presumed to be the signal your amp will be fed.


Current drive is calculated knowing the drive voltage and the impedance of the headphones.

You may wish to investigate common collector amplifier circuit topologies as the final output stage of your amplifier.
In tubespeak, that's a cathode follower.

[Maria]

Hello Cmjohnson, Thanks for your reply.

OK, I will try the common collector amplifier circuit for the final output stage on the amplifier. And let you know my update here.

Thanks again for guiding me.