Avoid Potential Groundloop Problems in Headphone Amp

[mattwalston]

I'm looking to start a project building a small headphone amp with 4 inputs combined. The amp will potential share a power source with the input devices and I'm unsure as to how good of a ground reference the devices will have due to small conductors, long wires, and automotive fuse blocks.

Since I'm starting from scratch, what design considerations should I incorporate into the amp to avoid issues with ground loops? The only option I'm familiar with is 1:1 transformers, but it's hard to find decent ones that are small.

My skill level is novice-intermediate. I've got a strong electrical background, but less strong with the electronics. I've repaired countless devices but this is my first real ground up project.

[Mooly]

If you could perhaps post a circuit we might be able to better advise...

The answer to correct grounding is to imagine and treat all conductors and wire as resistances. Length of wire doesn't really matter as you can design that out of the equation with good wiring practice. Even a 1cm piece of wire has enough resistance to introduce hum if the wrong things are connected to each end.

There's no magic involved, it's all common sense once you understand the mechanisms at work.

I would definitely recommend you get hold of a copy of Doug Selfs book on power amplifier design as that covers all of this. Libraries will often get a copy for you.

The Audio Power Amplifier Design Handbook

[mattwalston]

Thanks. Requested book on inter-library loan.

Originally Posted by Mooly

If you could perhaps post a circuit we might be able to better advise...

The answer to correct grounding is to imagine and treat all conductors and wire as resistances. Length of wire doesn't really matter as you can design that out of the equation with good wiring practice. Even a 1cm piece of wire has enough resistance to introduce hum if the wrong things are connected to each end.

There's no magic involved, it's all common sense once you understand the mechanisms at work.

I would definitely recommend you get hold of a copy of Doug Selfs book on power amplifier design as that covers all of this. Libraries will often get a copy for you.

The Audio Power Amplifier Design Handbook

[Mooly]

Thanks for the update, the book is a good read... enjoy

So is this one too on small signal design,
The Audio Power Amplifier Design Handbook

[AndrewT]

Originally Posted by Mooly

................I would definitely recommend you get hold of a copy of Doug Selfs book on power amplifier design as that covers all of this. Libraries will often get a copy for you.

The Audio Power Amplifier Design Handbook

makes my second edition look old hat now.
Although I do have copies of all the relevant pages/sections to bring it up to 4th edition.

[Mooly]

Originally Posted by AndrewT

makes my second edition look old hat now.
Although I do have copies of all the relevant pages/sections to bring it up to 4th edition.

I was think that too... I'd like to see the Class XD details laid out.