do i need to connect anything to AC earth ground in a non-metal chassis?

[el_matt0]

i just threw together a sOHA/ jisbos / alien dac build, and its housed up in a bit of a DIY chassis made of plexiglass. do i need to connect anything to the IEC ground lug or do i simply leave it open? i did consider the possibility of maybe connecting my signal ground or something to it, but im really unsure so someone who knows better should probably advise! cheers

 

[Daveze]

Ground pad on the SOHA board.

 

[amb]

The purpose of connecting a metal chassis to AC earth is for safety, in case a live AC mains wire comes loose and touches the case or some other component, the high voltage will be shunted to earth where you could touch (the case).

A totally plastic enclosure is non-conductive so you can't touch anything to get shocked (except, perhaps, a metal volume knob which might be electrically connected to signal ground, and that may or may not be affected by a loose AC wire). Thus, it's up to you whether you want to connect the AC earth or not. Doing so does add the possibility of a ground loop. Many commercial home-audio gear have two-prong AC plugs with no connectivity to AC earth at all, even those with a metal chassis.

 

[Rescue Toaster]

Unless you can be absolutely certain that no single component failure (and in as many cases as possible even multiple failures) could result in AC being exposed on RCA/headphone jacks, USB jacks, etc... you should always earth your signal grounds. Commercial equipment that lacks a ground but has exposed metal parts is tested to meet UL Class 2 (double insulated) and it's not easy for a DIYer to verify that your device would be safe under all likely failure conditions.

There are less dangerous ways to defeat ground loops. Also since it's a combined DAC/preamp/output stage ground loops are much less likely. And you're connecting to a PC and you don't want to risk damaging your computer. A side effect of this is that the shield on the USB cable WILL be earthed by your computer, so if your equipment isn't earthed itself your USB shield will carry all leakage current generated by your supply transformer and in some cases could cause unreliable USB communication depending on the design of your supply.

 

[Uncle Erik]

Quote:

Originally Posted by Rescue Toaster /img/forum/go_quote.gif Unless you can be absolutely certain that no single component failure (and in as many cases as possible even multiple failures) could result in AC being exposed on RCA/headphone jacks, USB jacks, etc... you should always earth your signal grounds. Commercial equipment that lacks a ground but has exposed metal parts is tested to meet UL Class 2 (double insulated) and it's not easy for a DIYer to verify that your device would be safe under all likely failure conditions. There are less dangerous ways to defeat ground loops. Also since it's a combined DAC/preamp/output stage ground loops are much less likely. And you're connecting to a PC and you don't want to risk damaging your computer. A side effect of this is that the shield on the USB cable WILL be earthed by your computer, so if your equipment isn't earthed itself your USB shield will carry all leakage current generated by your supply transformer and in some cases could cause unreliable USB communication depending on the design of your supply.

I agree.

Ground that sucker. Ground anything that uses wall current. If you get a ground loop, deal with it directly. You are always better off with grounded equipment.

Also consider that you're not the only one who will come in contact with the amp. Maybe not today, but 10 years down the road you might have a child with curious fingers. Or you might give it to a friend or sell it or whatever. It is best to ground it.

 

[amb]

Whatever you do, treat AC mains wiring with respect. Use heatshrink and looms on wires, insulated FastOn connectors, route the wiring so that they are not under any stress/strain, make sure they are all mechanically-secure so there is no chance of anything shaking loose, etc. Rather than relying on AC earth to save you (and it's certainly a good idea to do so), make your build solid so that a chance of failure is almost next to nil under virtually all conditions. Fuse the AC line!

 

[gjavitt90]

i thought in a soha you can ground the case but you shouldn't ground the amp, because it uses starground techniques, which are better or something. does anyone know anything about that?

 

[cgrums]

Quote:

Originally Posted by gjavitt90 /img/forum/go_quote.gif i thought in a soha you can ground the case but you shouldn't ground the amp, because it uses starground techniques, which are better or something. does anyone know anything about that?

A 'star' grounding scheme is a means of eliminating ground loops and the hum induced by them. This involves tying all signal/power supply grounds to the chassis at only one location, but it still involves making a ground connection to the amp. The AC earth is then connected to the 'star' point as well. As mentioned above, for safety practices it's not a bad idea to ground the amp to AC earth ground.

 

[dBel84]

Some of the concerns with the SOHA was that tying the center tap of the transformer to the line ground induced nasty hum. A way to deal with this is to use a ground loop breaker between the amps ground ( star or multiple ground nodes ) and the mains earth..dB