Eliminating Battery Charger Noise on DIY Stereo

Hey,

I'm currently working on a DIY stereo that will be powered by a 14.4V NiMH battery pack. I've already built a previous stereo with a similar design and the same style of battery pack, which I recharge with a "smart charger" I purchased online. My problem is this: If I turn on the stereo when the battery is charging, the charger produces noise on the line. I suppose this should be expected, as there is nothing regulating the power to the amplifiers (in this case, dual TDA7240A ICs), so the charging voltage is not only going to the battery, it's going right into the power supply for the ICs, decidedly not the best design. So I'd like to fix it in the next stereo. Is the solution as simple as adding a voltage regulator? If this is a solution, I'm thinking I'd want to use a regulator rated for the voltage of my battery pack (14.4V+). Is this a sound approach?

Thanks, SCW

Most decent IC audio amps already have a tremendous ability to reject voltage variation on the supply (see PSRR spec on the data sheet). Your problem is likely a "ground loop", which is caused by the layout of your wiring...

If your amp is homebrew (and hence has no PSRR), then voltage regulation may help. Any linear voltage regulator has a spec on "dropOut" voltage, which means that your regulated output voltage MUST be lower than the unregulated input voltage by some "headroom".