Help selecting an amplifier IC

Hi Jimmy,

I recently ordered in a couple of these and found them to work pretty good:

https://www.ebay.com/itm/LM386-MINI-Mono-Amplifier-Module-3V-12V-US-Seller-Fast-Shipping/111745624072?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The jack in the illustration is actually the input. The speaker is output on a couple header pins. If you are talking stereo you would have to use two of the boards. I don't know if you are suppose to build the amp yourself but in either case the LM386 is pretty widely used for low power headphone applications.

John

Thank you, I will look into it. From the data sheet of the LM386, it can provide 325mW at 6V. So is an amplifier chip that has between 100mW and 500mW adequate for most headphones?

One other thing is that I'm not sure If I can use that module, only because we are making our own PCB. I'm not sure how to attach the module. Unless I can?

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

Hi Jimmy,

Do you have any old cassette or CD player that you could open up and see what chips are being used for the audio output. I am not sure you want the job of designing a complete audio amplifier. The LM386 is about the simplest to build an amplifier around. If you are suppose to build it yourself the LM 386 would be the best choice in my opinion. If you are allowed to borrow a design another good choice would be the small stereo amp inside the omnipresent home desk top computer speakers. I have used these successfully for several projects.

John

I couldn't find information on the omnipresent speakers you mentioned. My friend just told me that the DSP itself is .9Vrms or 2.5V peak to peak. So at this point, 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 headphones like the Sennheiser HD 600 (300 ohms).