max98357 + headphones output + line out

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emmanuel63

Well-known member
Hello,

I have made a small synth powered with a little i2s classD amp : max98357. This amp is driving a small speaker.

I am afraid this is not possible with this type of amp, but is there any way to add headphones output + line output from the max98357 ?
I know this canot be done simply by adding resistors. Is there something I can try ?

Emmanuel
 
Headphones may be possible, since the headphone ground doesn't necessarily need to be connected to Teensy's GND. Most headphones have 3 wires: tip (left ear), ring (right ear), sleeve (common). You could try just connecting tip and ring to the positive output (called "A3" in the MAX98357 datasheet) and the sleeve to the negative output ("B3" ).

Line output is harder. I would not advise it. This sort of amplifier has a lot of high frequency output, which is (usually) ok if driven to a speaker, buy may or may not cause problems if sent to other equipment which expects a normal analog signal.
 
Thank you Paul.

I think I am going to add an i2s DAC (PCM5102) to get a proper line output.
Do you think I can share the same i2s wires for both the i2s amp and i2s DAC (BCLK, LRCLK, DIN) ?

Emmanuel
 
Thank you.

I think the PCM5102 will be automatically set to slave mode if I connect the System Clock pin (SCL) to ground. I will try that and report.
 
It works.

I have used a UDA 1334 DAC. This is perfect for line output. It is also known to be OK for driving headphones (even if it is not designed for it).
 
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