This Grounding Thing

[mlucitt]

Improved Grounding Scheme on Stock PL400

A member from Central Ohio asked me to conjure up a drawing for an improved grounding scheme for a PL400 that has not received a White Oak Audio main board (why would anyone want one of those?) Anyway, with no other modifications, this would be the improved grounding scheme for a "stock" PL400.

This method separates the inputs by giving them individual paths to ground. It also brings all grounds to a "star" connection to prevent ground loops, and floats the chassis with a reference to ground through a low-value resistor in case of an internal short-circuit. This is as simple as I can make it and still reduce the grounding anomalies; I strongly recommend a three-prong power plug and cord with the long ground wire firmly connected to the chassis so if there is a pull on the cable, it is the last wire to break.

Mark

 

[Gepetto]

A member from Central Ohio asked me to conjure up a drawing for an improved grounding scheme for a PL400 that has not received a White Oak Audio main board (why would anyone want one of those?) Anyway, with no other modifications, this would be the improved grounding scheme for a "stock" PL400.

This method separates the inputs by giving them individual paths to ground. It also brings all grounds to a "star" connection to prevent ground loops, and floats the chassis with a reference to ground through a low-value resistor in case of an internal short-circuit. This is as simple as I can make it and still reduce the grounding anomalies; I strongly recommend a three-prong power plug and cord with the long ground wire firmly connected to the chassis so if there is a pull on the cable, it is the last wire to break.

Mark

Not sure what the 2.2 ohm is Mark? Otherwise follows the WOA prescribed ground scheme.

 

[mlucitt]

I have seen the low-value resistor used in other manufacturer's gear, it is installed instead of a straight wire to partially isolate the chassis from the signal path of the output and other grounds. I cannot explain it in engineering terms but it seems logical to me. The low value will block low levels of EMF but not the higher voltages if a short-circuit occurs. Am I all wet?

Mark

 

[laatsch55]

Depends on where you're standing....

 

[Gepetto]

I have seen the low-value resistor used in other manufacturer's gear, it is installed instead of a straight wire to partially isolate the chassis from the signal path of the output and other grounds. I cannot explain it in engineering terms but it seems logical to me. The low value will block low levels of EMF but not the higher voltages if a short-circuit occurs. Am I all wet?

Mark

Hi Mark
That usually occurs in gear where there is a third safety ground pin from the AC cord attached to the chassis where you want to have a quasi-connection between chassis and analog ground to occur. In the case of the PL, the chassis is not safety grounded and serves more as an overall shield to external noise coming in. In that case, you want as solid a ground as you can get.

2.2 ohms is not a high value so will do no harm. Was just wondering where that came from is all.

 

[mlucitt]

Joe,
Thanks, I did take that chassis isolation resistor from a drawing that had a three-conductor cord, so we are on the same page. I agree, with a two-conductor cord the chassis should be the shield and be at the same potential as the audio source ground. I wonder when connecting a two-conductor piece of equipment through an interconnect to a three-conductor piece of equipment if both of the cabinets are grounded through the three-conductor cord and, what would happen if a short occurred in either component?

Mark

 

[Northwinds]

There is no ground on the incoming AC. The PL's were not made to be grounded on the AC in. It could cause a lot of hum in the 60HZ range. In fact to battle ground loops PL recommended that you unplug it, turn the plug 180 and plug it back in. Yes there is a ground, the chassis is the ground point.

So this is probably why my Carver equipment is not 3 prong then! They say the same thing about reversing polarity with the plug if there is a ground loop. Well that eliminates a ground problem for sure right off the bat

 

[laatsch55]

MAYBE----YMMV.....

 

[laatsch55]

And at the last moment a 3 prong 12 gauge power cord was requested for Stephens 400. Do I chassis ground the 3rd prong or float it??

 

[Gepetto]

And at the last moment a 3 prong 12 gauge power cord was requested for Stephens 400. Do I chassis ground the 3rd prong or float it??

You can tie it to the chassis Lee IF AND ONLY IF this is the only piece of equipment that will be plugged into a 3 prong AC source. Else you will be chasing ground loop problems. The AC safety ground network is meant to be a safety ground only. Electricians that wire buildings don't give a rat's ass about your audio grounding considerations.

 

[Gepetto]

Joe,
Thanks, I did take that chassis isolation resistor from a drawing that had a three-conductor cord, so we are on the same page. I agree, with a two-conductor cord the chassis should be the shield and be at the same potential as the audio source ground. I wonder when connecting a two-conductor piece of equipment through an interconnect to a three-conductor piece of equipment if both of the cabinets are grounded through the three-conductor cord and, what would happen if a short occurred in either component?

Mark

If the short to the chassis occurred in the equipment with the 3 pronged plug, then the fault current would go right into the safety ground and trip the breaker at your box.

If the short to the chassis occurred in the equipment with the 2 pronged plug, then the fault current would flow through the shield of the interconnects between the components and into the safety ground of the equipment with the 3 pronged cord (which hopefully has a single connection between its analog ground and its safety ground) and then trips the breaker at your box.

The answer depends on how the grounds are interconnected on the one component with the safety ground.

 

[mlucitt]

Screw it down hard to the chassis, Lee. The chassis is the first line of defense for shock protection. If you have noisy mains, then a input line filter is needed. I like these from Mouser and they might fit into the PL400 chassis (barely).

Mouser P/N: 592-15EJS1 or 693-5110.1543.3

Mark

 

[Gepetto]

Screw it down hard to the chassis, Lee. The chassis is the first line of defense for shock protection. If you have noisy mains, then a input line filter is needed. I like these from Mouser and they might fit into the PL400 chassis (barely).

Mouser P/N: 592-15EJS1 or 693-5110.1543.3

Mark

If you use these filters though Lee, then you CANNOT float the chassis because there are Y-caps between line and neutral to the safety ground which create leakage current that normally flows down the safety ground wire. If you float it then half the AC mains voltage (60VAC) will appear on the chassis shell which presents both an audio and safety concern.

 

[mlucitt]

Good point Joe. Even though Lee could use a good jolt now and then to keep his BP up, his customers might not appreciate it.

Lee, what Joe said.

Mark

 

[laatsch55]

So ground it immediately with no filters.

 

[laatsch55]

Good point Joe. Even though Lee could use a good jolt now and then to keep his BP up, his customers might not appreciate it.

Lee, what Joe said.

Mark

Thanks Matk, you're a peach bud.

 

[laatsch55]

You can tie it to the chassis Lee IF AND ONLY IF this is the only piece of equipment that will be plugged into a 3 prong AC source. Else you will be chasing ground loop problems. The AC safety ground network is meant to be a safety ground only. Electricians that wire buildings don't give a rat's ass about your audio grounding considerations.

Of course we don';t, long as nobody gets fried it's all good, till some one plugs in s damn stereo!!!

 

[speakerman1]

When I do an IEC conversion I ground to the chassis. What I plug it into usually will trip before the CB. I run conditioners that will trip. Yea Lee a hot ground isn't fun. I can see your hair standing on end.

 

[laatsch55]

It's pretty used to that profile Larrt....

 

[speakerman1]

EMF coming off transformers. In the Homemade preamp or whatever it is. The Kit. I wrapped the toroidal with 1/4 inch lead. The reg. I covered the top and sides. The toro I just wrapped the sides. Could it make a difference. I did it w/o even listening hard. It couldn't hurt could it? Lee do you have a dedicated grd. rod on your stereo circuit. Aircraft grd.s are important. Everything has it's own grd. point. Working avionics you carried a burnishing brush to get good grd.s. 120vac 400 cycles. It don't knock you back. It holds onto you. You are running florescent lights without noise. No interference on instruments and communications. The gens are 3 phase hooked to a CSD. Tracking down a bad grd. can take days. Cannon plugs are even grd. on the back shell.