Help needed with haptic driver design

Audioguru again

Joined Oct 21, 2019
You are making some statements in this that to my simple mind don't add up. How can 30KHz be 2hz at the same time? Or are you meaning your giving a 30KHz wave for 2Hz as a burst? 30KHZ will be moving so fast it will seem to be only moving as a snap action.
The PAM amplifier has a class-D output which is a 250kHz squarewave with its pulse widths modulated by the audio. If the audio is a 2Hz sinewave then the pulse widths will change the same as the 2Hz sinewave. Usually the output filters away the 250kHz but the speaker will also filter it away.


Joined Aug 21, 2017
Haptic? You are very near to the frequency range where some frequencies induce the unstoppable panic attack, some are making the heart attack, some are instantly destroing the liver or what-s-know-what. Just be careful with and visit the notarius before the push Your switch button on.

Thread Starter


Joined Nov 23, 2019
Thank you everyone that has given advice on this topic. As I said earlier I got the set up working great with the older PAM8402 by shorting out the coupling capacitors and biasing the input PWM wave at 2.5V. I am able to drive a small 8 Ohm audio exciter backwards and forwards throughout its entire "throw" at very low sub Herz frequencies. At full extension the amp is actually delivering around 400mA which is more than expected! - the drivers get fairly warm after a bit of running but the little amplifier chip seems perfectly fine.

However, I just received some 8403 amps to get a little extra power and multiple channels. I prepared them the same way and shorted out the input coupling capacitors so that I could get nice low frequencies. However when I tested all the paths in my circuit before switching everything on (just to check I hadn't shorted anything) - I noticed that the "Vref in" and the "V-" (power) to the 8403 have zero resistance between them.

I thought that I would be able to bias the input like with the Adafruit PAM8402 board that I used earlier, but this packaging of the PAM8403 (just a generic green one made in China from Amazon) - seems to only allow "Vref in" to be the same ground as the V-. This appears to stop me driving the speaker in both directions.

Do you think I am missing something - or is there an easy fix to this? I could revert to having mulitples of the PAM8402. I want 4 channels in all - but would like the extra power and smaller size of the PAM8403 if possible