Electronics > Beginners
Audio amp help
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oPossum:

--- Quote from: jeffheath on February 12, 2019, 09:23:26 pm ---The impedance is about 30 ohms, so I think something like this lm386 amp might work, but my concern is that this, as well as the cmoy amp, are meant to be preamplified, (like from a smartphone) and won't amplify from "line level" audio.

--- End quote ---

They would probably work just fine as designed for headphone amp use. If you need more gain it is usually just a matter of changing the feedback resistor. (LM386 is an exception to this, it has 2 selectable fixed gain settings.)


--- Quote from: jeffheath ---I looked at the data sheet for the MAX97220 and was wondering if I could just add a ganged potentiometer as shown, (for volume control) or if there's "more to it than that"

--- End quote ---
That is all that is needed. Use an audio taper pot rather than linear taper.

If you choose to use a Class D amp, be sure to carefully read and follow the PCB layout guidelines. They can be sensitive to layout and not work properly with a bad PCB layout.
Richard Crowley:
Here is a nice stereo (dual) 10K audio-taper pot from a North American source.  $1 
https://www.allelectronics.com/item/apt-10kd/10k-x-2-audio-taper-potentiometer/1.html

And here is a complete headphone amp board all assembled and tested for $2.
https://www.amazon.com/TDA1308-Headphone-Amplifier-Headset-Preamplifier/dp/B07KMBZDYT
L_Euler:
You can use one of these: TPA 6021A4
Typically used for speakers integrated in computer monitors and can also drive headphones.  The full data sheet offers example circuits for speaker and headphone outputs.
Richard Crowley:

--- Quote from: oPossum on February 13, 2019, 01:15:07 am ---LM386 is an exception to this, it has 2 selectable fixed gain settings.
--- End quote ---
The LM386 can be set for any gain between 20 and 200 using a capacitor and resistor. See the data sheet for details.


--- Quote ---If you choose to use a Class D amp, be sure to carefully read and follow the PCB layout guidelines. They can be sensitive to layout and not work properly with a bad PCB layout.
--- End quote ---
Yes this can be a "trap for young players" and not necessarily a good beginner project.  But there are assembled and tested PC boards with the chip and all the passive components for barely more than the cost of the bare chip.
tooki:
With class-D amps, buy one made specifically as a headphone amp. The ones for speakers generally do not allow you to bridge the two negative outputs for the L and R, as is normally needed in headphones. (To do it, you have to, at minimum, add a resistor network.) So it's better to just get a purpose-built one.
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