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Old 10th November 2010, 04:29 AM   #1
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Default Adding a ground with a 3 prong cable and connector

I want to add a true ground to my magnavox 185-AA amp that Ive been modifying by adding a ground from the power connector
Ive added a PC D style power connector and would like to connect the ground pin and add proper ground to this amp
From what ive read I need to disconnect the capacitor from the ground in this schematic:
Click the image to open in full size.

Would that be correct?
Im going to also replace this capacitor with a new one anyway so would a normal 2 prong cap work since Im planning to remove the ground?

thanks in advance
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Old 10th November 2010, 06:11 AM   #2
jfitz57 is offline jfitz57  United States
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Quote:
Originally Posted by mackinthebox View Post
I want to add a true ground to my magnavox 185-AA amp that Ive been modifying by adding a ground from the power connector
Ive added a PC D style power connector and would like to connect the ground pin and add proper ground to this amp
From what ive read I need to disconnect the capacitor from the ground in this schematic:

Would that be correct?
Im going to also replace this capacitor with a new one anyway so would a normal 2 prong cap work since Im planning to remove the ground?

thanks in advance
Those capacitors (10000mmf = .01uf) in the original design are to keep the chassis at R.F. ground no matter what way you plug it in.
If you ground The chassis with a 3 wire power cable you don't need any capacitors.

But you may create a new problem called ground loops unless everything that you have connected to that anp is connected to the same outlet or is floating.

Jim
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Old 10th November 2010, 06:50 AM   #3
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Let me also add that the engineers have designed this equipment to operate properly without an added grounded plug.

So to say, what ain't broke, don't fix it!
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Old 10th November 2010, 07:17 AM   #4
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ok thats what i thought
I will give it a try and if it doesnt work correctly I can just replace the cap with a new one

Last edited by mackinthebox; 10th November 2010 at 07:20 AM.
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Old 10th November 2010, 12:52 PM   #5
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The .01 uF cap will only pass 0.5 mA at 120V, so it isn't a shock hazard, and it's a ceramic, not a potentially leaky paper type, so you could leave it alone...

But of course if that amp were manufactured TODAY, a 3-wire grounded cord would be required by safety standards!
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Old 10th November 2010, 01:44 PM   #6
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that why i want to install one, plus from everything ive read on other forums whenever someone adds a ground they trip breaker unless they remove that cap from ground
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Old 10th November 2010, 02:20 PM   #7
TheGimp is offline TheGimp  United States
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You could install a low value resistor (say 100R) in parallel with two antiparallel 3A diodes from the ground terminal of the power connector to the chassis.

This elevates the chassis for noise but still allows a low impedance path to blow the fuse in the event of a hot "short to chassis".
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Old 10th November 2010, 02:25 PM   #8
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what purpose do those capacitors actually serve?
ive never seen anything like it in any other devices ive opened up
but then ive never dealt with circuits this old...
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Old 10th November 2010, 03:15 PM   #9
DF96 is online now DF96  England
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See post #2 - RF ground for chassis. If present these must be modern mains rated capacitors, which are self-healing and guaranteed to fail open-circuit. 0.5mA of AC is enough to give you an unpleasant tingle, especially if you are not expecting it. If the capacitor fails short-circuit, or develops excessive leakage, then it gets more dangerous if the mains polarity is wrong.

If left in place after a true ground is added it may trip an earth leakage circuit breaker.

For safety, remove the cap and add a chassis ground. Then you have the fun of eliminating a ground loop from your system!
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