crate sound - headphone amplifier

duinotech PAM8403 amplifier module as headphone amplifier
Photo: Barry Ramage

The Crate Theatre sound is delivered through headphones, while I have been wanting to make myself a portable high fidelity headphone amplifier for some time, I needed to use parts available locally.

Enter the Duinotech 2 x 3W PAM8403 IC amplifier module, $5.00 locally...

There are many posts on the web stating that is not possible to common the output ground on the PAM8403 IC for use with 3 pole jack connectors, full H bridge output etc. I tried two options before finding a near working solution.

So, what DIDN'T work:

These two examples are taken from this post at StackExchange

Half bridge taps. Nice Idea, very clean layout, my test result: massive pops and distortion.

half bridge amp option PAM8403 IC
Fritzing Sketch: Barry Ramage

This idea wouldn't be ideal for The Crate Theatre anyway in that WS2812B LED are used for lighting. Common ground setup would create noise in the audio system in the same way dimmers interfere with audio signals when on the same phase in full scale setups.

What DID NEARLY work:

This approach was tried, massive cross talk between left and right.

load on ground PAM8403 IC headphone amplifier
Fritzing Sketch: Barry Ramage

Quite nice other than the cross talk, my test used 10R resistors, as that is what I had. As the post mentions, playing with capacitor values may improve bass response.

While it may be possible to get better results by changing some of the component values in the two examples above, my capacitor stock was low, so, onward...

Circuit to allow use of headphones.

While this post on edn.com is referring to the MAX9704 IC, it worked perfectly driving headphones with the PAM8403 chip.

On the schematic we are only dealing with the output components, the input components (or very close to) are already on the modules pcb.

Very few components, unperceivable L R cross talk, SNR comparable with unmodified board.

Unfortunately low level output, lower than the input!

crate theatre headphone amplifier schematic
Fritzing sketch: Barry Ramage.

So, if your need is to plug headphones into a speaker amp, great.

For the crate however, rewiring the headphones with two 2 pole connectors or a single 4 pole connector and thereby seperating the common ground is the way to go using this chip.

My second option is to go with option two and ignore crosstalk.

If anyone else has experemented with class d headphone amplifiers, maybe we can expand upon this page.