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Topic: Buzzing in my headphone amp while laptop charging (Read 1699 times) previous topic - next topic
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Buzzing in my headphone amp while laptop charging

I bought an FiiO A3 a few months ago.  I've used it with my laptop all the time when I listen to music in bed.

Well, today was the first time I used it while the laptop was charging.

And boy did I get a lot of buzzing.  If I plug the headphones in directly, then I don't get any buzzing at all, only when the amp is plugged in.

If I disconnect the power and just run off laptop battery, then the buzzing goes away.

So, 2 questions:

1. Why am I only hearing the buzzing through the amp, not when headphones are plugged in directly?

2.  Is there any kind of inline filter I can buy to eliminate the buzzing?

Equipment:

Amp:  FiiO A3 battery powered headphone amp
Laptop:  Lenovo Thinkpad T440
Charger:  Lenovo provided Thinkpad charger
Headphones:  Sennheiser Amperior

Buzzing in my headphone amp while laptop charging

Reply #1 –
Its possible your laptop and your amp are trying to pull the headphone "ground" to different absolute potentials.  This is pretty common on low voltage audio amplifiers (e.g. stuff powered off of 5 or 12 v).  When you run off of battery it doesn't matter since the amp just floats at some level above your AC ground (probably half the supply voltage), but when you plug the amp into the wall, suddenly the amp and the laptop disagree on where ground is, and whichever one is stronger wins by pumping current into the other.

You could try putting a blocking capacitor in series with the ground line on your laptop's line/headphone out

Buzzing in my headphone amp while laptop charging

Reply #2 –
Quote from: saratoga on
Its possible your laptop and your amp are trying to pull the headphone "ground" to different absolute potentials.  This is pretty common on low voltage audio amplifiers (e.g. stuff powered off of 5 or 12 v).  When you run off of battery it doesn't matter since the amp just floats at some level above your AC ground (probably half the supply voltage), but when you plug the amp into the wall, suddenly the amp and the laptop disagree on where ground is, and whichever one is stronger wins by pumping current into the other.

You could try putting a blocking capacitor in series with the ground line on your laptop's line/headphone out


Well, it looks like the problem goes away when the battery gets above around 25%.  I turned the amp back on when the battery was around 27% and the problem was gone.  My battery was as 6% when I first plugged the amp in.