The most naive approach would be to change the cord and connect pin 3 to the chassis. My concern, because I don't yet have a full understanding of grounding, is, would this cause negative performance changes to the circuit, since it was not designed with an earth ground in mind? What sorts of factors would go into such a consideration?
The short answer to your question is: most, but not all, ungrounded devices can be converted to grounded, and there are safety and performance consequences if this is not done correctly. You are not allowed to connect to ground the so called "hot chassis" devices: on those devices, there is no galvanic insulation between mains and chassis. This means: you will measure a low resistence between the chassis and one or both power leads, on some cases even while the power is off. This was common in the last century, but rare on today devices. If you connect to ground a hot chassis device, the mains circuit breaker will trip and/or the safety ground feature is defeated.
If the device is not a hot-chassis one, then the chassis may be connected to ground, but where and how you connect the ground wire of the power cord to the chassis is important. This is also very closely regulated. I know the CE regulations only, but UL regulations should be similar. The main concept is this: in the event of failure a very high fault current will briefly flow on the ground connection, so the wire needs to be at least the same size of the mains wire and must be attached to the chassis very well, otherwise the connection will vaporize or the circuit breaker will not trip in a timely fashion, and fire could start. As example, if the chassis is painted and a hole needs to be drilled to attach a new properly sized ground screw, then the paint must be scraped around the hole to ensure the best possible contact with the screw and nut. Another consequence of a faulty or poorly implemented grounding is the increase of background noise on audio devices. This may have several causes such as ground loops (hum) and radio frequency injection to the device trough the groud connection. A common cause is a faulty outlet that does not draw to ground the leakage current generated by the input electromagnetic interference filter of another device connected to the same outlet.
If the device is not a hot-chassis one, then the chassis may be connected to ground, but where and how you connect the ground wire of the power cord to the chassis is important. This is also very closely regulated. I know the CE regulations only, but UL regulations should be similar. The main concept is this: in the event of failure a very high fault current will briefly flow on the ground connection, so the wire needs to be at least the same size of the mains wire and must be attached to the chassis very well, otherwise the connection will vaporize or the circuit breaker will not trip in a timely fashion, and fire could start. As example, if the chassis is painted and a hole needs to be drilled to attach a new properly sized ground screw, then the paint must be scraped around the hole to ensure the best possible contact with the screw and nut. Another consequence of a faulty or poorly implemented grounding is the increase of background noise on audio devices. This may have several causes such as ground loops (hum) and radio frequency injection to the device trough the groud connection. A common cause is a faulty outlet that does not draw to ground the leakage current generated by the input electromagnetic interference filter of another device connected to the same outlet.
Thank you, that's very helpful! Can a resistor or diode be placed in the path to ground to prevent loops or interference?
If a device provides switched or unswitched secondary outlets, can they be converted to grounded, and connected to the same ground wire?
Thank you again for the info!
If a device provides switched or unswitched secondary outlets, can they be converted to grounded, and connected to the same ground wire?
Thank you again for the info!
This is pretty easy to answer - as long as the device has a mains transformer. Go ahead and connect that ground wire to the chassis.
Now if the device is designed to run two - wire polarized (as evidenced by one prong being wider) connecting earth to chassis can create a ground loop when this device connected to others.
I'm imagining I/O connectors with a chassis connection; now there's an AC socket to device, interconnect to other 3-wire corded device, back to AC socket loop. You can always plum 'em all into the same extension strip, to minimize the loop length.
And why do you want to malign said device for 3 wire cording? Electrical Safety?
Now if the device is designed to run two - wire polarized (as evidenced by one prong being wider) connecting earth to chassis can create a ground loop when this device connected to others.
I'm imagining I/O connectors with a chassis connection; now there's an AC socket to device, interconnect to other 3-wire corded device, back to AC socket loop. You can always plum 'em all into the same extension strip, to minimize the loop length.
And why do you want to malign said device for 3 wire cording? Electrical Safety?
It's best to read up on and understand proper electrical codes, and how grounding is implimented.
If you have no background or experience in such things, you're liable to cause a dangerous situation.
Skipping such education is, to put it plainly, dumb.
If you have no background or experience in such things, you're liable to cause a dangerous situation.
Skipping such education is, to put it plainly, dumb.
Partly because I'm curious to know if it can be done. Is there any reason for a device not to be grounded?
More directly, I'm working on a preamp with several secondary outlets provided, and it would be cool to switch them to three-prong so they would be more useful in todays world.
It may be workable to fit 3 prong outlets with safety ground for equipment that requires it without actually connecting the ground to the preamp chassis thus preserving the original grounding scheme.
Note, I am not suggesting that this is the best scheme nor whether your preamp would be better or worse with an added ground connection.
The bible on grounding -
Audio Component Grounding and Interconnection - diyAudio
Note, I am not suggesting that this is the best scheme nor whether your preamp would be better or worse with an added ground connection.
The bible on grounding -
Audio Component Grounding and Interconnection - diyAudio
Only for DIY would/could you insert an impedance in the IEC safety ground to chassis connection.
A diode block is safest because it won't burn up before the fuse blows.
Otherwise, use a wire bolted directly to the chassis, larger than (or the same size as) the line cord.