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Headphone Amplifier circuit problem

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Headphone Amplifier circuit problem

Postby Christofer » Wed Aug 16, 2017 3:06 pm

Hi, in my first post- need help or advice for 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. (According to a datasheet of 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.
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Re: Headphone Amplifier circuit problem

Postby organtechnology » Wed Aug 16, 2017 4:06 pm

Christofer wrote:Hi, in my first post- need help or advice for 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. (According to a datasheet of 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.


Hi,

Treat it as an audio op-amp and set the gain with the feedback resistor values.

Thomas
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Re: Headphone Amplifier circuit problem

Postby NickNelson » Thu Aug 17, 2017 5:56 am

I'm not sure why you are worried about the minimum voltage to the headphones, you can't damage them by underdriving. The problem would be accidentally overdriving them with possible damage to either the headphones, or your hearing or both.

Personally, I would start by assuming that the incoming audio signal will be about 1V peak and, based on the power handling capabilities and impedance of the headphones, calculating an appropriate voltage to drive the 'phones. This will give a reasonable starting point for the gain.

It will almost certainly be necessary to 'tweak' the gain subsequently to suit the actual conditions in use.

Nick
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Re: Headphone Amplifier circuit problem

Postby Christofer » Thu Aug 17, 2017 12:34 pm

Thanks a lot for your kind reply.
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