Guitar humming (not in a good way)

[Paul Douglas]

I've been building lap steels for a little while now and I've just finished my fourth. It's by far the best so far, and the first to have all good quality components. I'm generally pleased with it except for the fact that it makes a terrible noise - more of a buzz or crackle than a hum, really.

I know this is a very common problem and I have had it before, but this is different because it completely goes away if I use a wireless link between the guitar and the amp. I've been using this a lot lately, it's better for me than cables, but the wireless thing I have is a cheap one and it tends to cut the high frequencies a bit. That's why I thought I'd try the new guitar with a wired connection, otherwise I'd never have noticed the hum. I plugged it in and it immediately started making a racket. Previously, I've had hum issues and they generally stop if I touch something metal on the guitar, but this time it gets worse if anything.

I've tried different cables. I've tried using a different amp - a battery one so there is no mains hum issue. I've inspected all the wiring and everything looks fine, and trying to ground various bits of it makes no difference. It's a humbucker pickup so not a single coil problem. The only thing I can think of is that the pickup has fairly long unshielded leads. I'm reluctant to cut them short because I'll probably be moving it to the next home-made guitar in due course, so they are just stuffed into the cavity under the controls.

I'd be grateful for any suggestions for what might be causing this. It doesn't matter a great deal because I'll be using it with the wireless link, but I'd like to correct the matter if I can.

Thank you.

[Dave Grafe]

It sounds like your guitar's ground is connected to the hot (tip) side of the 1/4" jack instead of the sleeve contact. Your wireless transmitter may have a floating ground scheme but any wired connection must be wired correctly.

Don't cut the wires yet but do twist them tightly to help cancel interference, they are not the issue here. Remember that the bridge and strings, and tone capacitor if included, need to be well grounded to the sleeve contact of the 1/4" jack as well as the low side of the pickup, and only the high side of the pickup and tone pot wiper (or switch to such) should be connected to the jack's tip contact.

Check your wiring scheme and remedy any cold solder or otherwise faulty connections and get back to us.

[Paul Douglas]

It sounds like your guitar's ground is connected to the hot (tip) side of the 1/4" jack instead of the sleeve contact. Your wireless transmitter may have a floating ground scheme but any wired connection must be wired correctly.

Exactly the problem. Thank you so much - I could have spent many hours looking for that as I simply wasn't aware that it might be the issue. I feel like a complete fool for connecting them the wrong way around but, otherwise, brilliant.

Didn't know anything at all about the floating ground thing but it obviously explains why the wireless worked.

Thanks again!