Help selecting an amplifier IC

Hi Jimmy,

A few milliwatts or low tens of milliwatts is sufficient for typical headphones or earphones.

Mobile phones only output a few tens of mW to the headphone socket, and that's good enough for typical earphones.

If I was doing it, I'd use the LM386 chip too, it is low-cost and plenty of examples online (although the datasheet is sufficient).

Otherwise, for stereo, you could even use almost any dual op-amp IC since they can provide this level of power output too. Hopefully you'll have

covered op amp circuits in lessons, you can prototype it on a breadboard block to test it.

If you're looking for something very high quality then check out semiconductor manufacturer websites for audio amplifier ICs, for instance Texas Instruments.

The datasheets contain the example circuits.

You could (should?) also consider I2S DACs with integrated headphone amplifier, since that DSP chip can output I2S. Again, silicon manufacturers like TI will have datasheets with schematics for such chips.

I think I saw the LM4881 as a good option because it supports two channel.

https://www.ti.com/lit/ds/symlink/lm4881.pdf?ts=1599512503820&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM4…

But I guess I'm confused about the units that are listed for headphone specs and headphone amp specs.

This is a link to the headphones I own. They are 50 ohms impedance planar magnetic. Under the specifications, the sensitivity is listed as 92dB/mW, and max input power is 3W.

I don't understand the confusion. Your headphones are not very sensitive. But what happens if you plug them into a mobile phone? If they work adequately, then you know that a few tens of milliwatts is sufficient, because that is all the mobile phone supports. If you want higher power, you can select an IC with higher power (it's in the datasheets).

When I plug my headphones into my phone or laptop, I can hear stuff on max volume but it's not loud enough. Why is that more power from my amp makes it also sound better?

https://service.shure.com/s/article/understanding-earphone-headphone-specifications?language=en_US#:~:text=Sensitivity%20indicates%20how%20loud%20the,a%201%20mW%20input%20signal.&text=A%20typical%20headphone%20output%20could%20provide%20this%20level.

This site says that 90 to 95dB is pretty loud enough, so if I wanted 92dB, my amplifier would only need to output 1mW to do that. Then why is so powerful then? A lot of amplifier ICs can output 100 to 200 mW of power, which would be seemingly unnecessary? It can't be because I am not understanding something.

It's a good question. Think about the simplistic answer at the site you're relying on, then consider what the spectrum of music looks like, and where the energy could be distributed, depending on what you're listening to. Then think about what could cause the output to not be loud enough, and what happens when the output from the amplifier starts distorting (and why that happens).

Ultimately, if you want the output to be louder, try changing the headphones, or try using an amplifier with higher power output (it's in the datasheets of each amplifier IC).

I am still looking for the appropriate IC for my project still, this was a side mission to understand the numbers. I have ruled out the LM386 because I would need two of them, and I am probably not going to use the LM4881 because the THD at 200mW is too high. Do you know of any ICs that could be good? All I have seen in TI chips

I am still looking for the appropriate IC for my project still, this was a side mission to understand the numbers. I have ruled out the LM386 because I would need two of them, and I am probably not going to use the LM4881 because the THD at 200mW is too high. Do you know of any ICs that could be good? All I have seen in TI chips

This conversation is getting a bit audiophile, meaning the conversation doesn't make any more sense technically to me.

I've yet to hear any normal headphones that don't function with a LM386 or a mobile phone. I have listened to $200+ head- and ear-phones and they sound fine with a typical mobile phone.

If the THD is too high, you'll have to search for a design which has lower THD. It won't make the project very hi-fi anyway, because if you were interested in that, you would not be using the in-built analog output from the DSP.

Sounds like the project just changed from a DSP amplifier to an audiophile headphone amplifier project.. in which case there are online schematics of such amplifiers you could examine (there are audiophile websites with these schematics).

Sorry if I am being scrambled in my thoughts and reasoning. You do have a point that this won't be the highest fidelity. It is still a DSP project, but if I can find an IC that will be good enough for headphones with 300 ohms like the popular HD600 from Sennheiser then it will be suitable. I just want enough power to make those have enough volume and decent enough sound quality. I'm not saying the LM386 can't because I don't know, but if you're comparing it to a mobile phone then I would be concerned. If it can outperform a mobile phone and drive higher impedance headphones decently, then I can use it. I initially said I might not use it is because it is mono. My friend is making the PCB and soldering the components so he said he would prefer 2 channel/stereo IC. The LM4880 or LM4881 is something we are looking into because it is stereo, but we are still looking.

Edit: My friend told me that the DSP itself is .9Vrms or 2.5V peak to peak. So, I don't think I need as much power as I was expecting, right? He was saying that this level can drive earbuds and low impedance headphones, but we still want to add another amplifier to drive higher impedance headphones.

jimmy5893  wrote:

 

good enough for headphones with 300 ohms

That's unrealistic. You're asking for some high power stereo chip to drive up to 3W for one set of headphones because a mobile phone type amplifier isn't good enough, and now to drive high voltage high impedance too, with THD requirement better than typical single-chip headphone amplifiers. I think you may have to design a custom circuit, or just use normal headphones.

3W is definitely too high of an expectation. I read that that the max power for the HD600 is less than .5W so that would be the maximum target at this point.