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Polarize plug, 3 wire or keep as is
Polarize plug, 3 wire or keep as is
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Old 15th May 2020, 09:18 PM   #1
Tommyboy60 is offline Tommyboy60
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Default Polarize plug, 3 wire or keep as is

A topic came up about changing over to the AC 3-wire plug on an old amp that has a non-polarized AC plug. What is the thought on this? Keep the original non-polarized, change to polarized or change to 3-wire. I have always thought about this but have never done made the change. I have told customers about reverse plug noise or about what the polarize switch does (if available) but never actually changed the plug. I think this is a good topic for this forum. I really like all the responses I have gotten for my Stromberg restore questions and I thank you all. Wish I knew about this site a few weeks ago when I did the Gibson GA40.
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Old 15th May 2020, 10:15 PM   #2
audiowize is online now audiowize  United States
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It's much safer to have the chassis earthed through the power cord. There are situations with items like the old AA5 radios where you need to add an isolation transformer to make this possible, but it's certainly worth the extra effort.
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Old 15th May 2020, 11:29 PM   #3
6A3sUMMER is online now 6A3sUMMER  United States
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There is no single correct answer.

1. Before you change anything, you need to have a complete and accurate schematic of the amplifier.

For example, does the amplifier (already) have a power transformer that isolates the amp from the power mains?

Based on the schematic, etc., there are some decisions to be made. Modification may require more than just a 3 wire cord (internal circuitry may need to change).

Depending on everything that will be connected to the amplifier, just using an isolation transformer to "Float" the amp, may be dangerous.

2. Next, you need to know how the amplifier will be used.
Electric Guitar?
Microphone?

Hi Fi?
Tuner, Phono preamp, line preamp?
What are the signal sources, are they floating or grounded?

3. Next, you need to know about your local mains power.
For example, does it consist of Hot, Neutral, and Ground?
Are the mains outlets wired correctly?
(some houses are mis-wired)
Does it use another power method (220v Hot, Hot, Ground)?

4. What are your countries regulations for power mains and plug-in products, like power amplifiers?
For example, if you were to purchase a brand new power amplifier in your country, would it come with a 3 wire power cord?

5. Safety First!

6. Prevent "Surviving Spouse Syndrome".
(Refer to 1 - 5 above)

Last edited by 6A3sUMMER; 15th May 2020 at 11:35 PM.
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Old 16th May 2020, 12:15 AM   #4
Tommyboy60 is offline Tommyboy60
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I use my isolating transformer almost every time I am working on equipment in my shop unless I know for sure I do not have a hot chassis.


I know this has nothing to do with equipment isolation but I did learn that the hard way many years ago. I remember asking my Dad back in the early 80's, advice on working around high voltage areas of a TV specially the ones with the power resistors that were mounted on cross bars when I first started repairing them. He said, "you have to be put against the wall a few times, then you will learn", and I sure was a couple times. Thanks Dad! He was very good at analog circuit repair. Even though I did learn a lot about analog during my EE college years, I learned more from my father and on the side with my professor than I did in college. My main study was Computers and Networks. I had a hard time with the capacitor because when I was an auto mechanic, we called it a condenser and all we knew about it was that if we threw it at someone you got a shock. My father help me get past that one then everything else fell into place. He had a hard time learning TTL logic, basic AND gate type logic, I helped him through that then showed him a gate array that had a window on top (a Digital Equipment chip where I was working as a Hardware Engineer), I told him this is where your going. In college on the side, I build a JK flip flop out of 11 NAND gates because I wanted to be able to see the inner workings of a JK. Back then the computers we had in college, the ALU, program counter, register etc... were all single boards with small scale components. We learned the sequence of events for a computer to wake up internally.
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Old 16th May 2020, 12:36 AM   #5
anatech is offline anatech  Canada
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Polarize plug, 3 wire or keep as is
Hi Tommy,
I wouldn't change it without a good reason. You can install a polarized plug, put the common towards the side with the highest leakage to keep the chassis leakage as low as you can. Of course if the outlet isn't wired properly, the opposite is achieved.

A grounded chassis is the safest, but you might create a ground loop if any connection is made to another amp or recording console. It goes without saying that no direct mains connection should ever go to the chassis. Remove the widowmaker capacitor of course!

-Chris
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Old 16th May 2020, 12:43 AM   #6
6A3sUMMER is online now 6A3sUMMER  United States
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There are some houses that have two-wire mains power outlets wired incorrectly,
Hot and Neutral are reversed. Who knew that? (someone was shocked to find out!)

And there are some houses that have three-wire mains power outlets wired incorrectly.
That is why they manufacture those three-wire mains power outlet safety testers (with the glowing lamps).

There are some three-wire IEC power cords that have been incorrectly wired.

Test your amplifier, test your power cords, test your mains power outlets; and test your friends mains power outlets when you bring your amplifier over to his house.

Using a polarized plug that is incorrectly wired on an amplifier, can cause the chassis to be connected to HOT!

Know thy devices and mains outlets, etc.
Or . . . Know thy maker!

Last edited by 6A3sUMMER; 16th May 2020 at 12:45 AM.
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Old 16th May 2020, 12:49 AM   #7
anatech is offline anatech  Canada
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Polarize plug, 3 wire or keep as is
Hi 6A3sUMMER,
Absolutely! It has happened. Anyone with older equipment should have a tester, every musician should carry one too.

-Chris
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Old 16th May 2020, 12:04 PM   #8
Burnedfingers is offline Burnedfingers  United States
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Quote:
Originally Posted by anatech View Post
Hi Tommy,
I wouldn't change it without a good reason. You can install a polarized plug, put the common towards the side with the highest leakage to keep the chassis leakage as low as you can. Of course if the outlet isn't wired properly, the opposite is achieved.

A grounded chassis is the safest, but you might create a ground loop if any connection is made to another amp or recording console. It goes without saying that no direct mains connection should ever go to the chassis. Remove the widowmaker capacitor of course!

-Chris
Exactly!

Did pro audio systems and there is nothing more frustrating than chasing ground loop problems caused by the 3 wire. Same is true with large commercial/industrial systems. I had one system once where I had to insulate the rack from the cement floor and use non conductive bolts to bolt the rack to the floor and employ a super neutral in order to get the noise down to nothing.

With audio you can always expect the unexpected. One system I did I had to use cheater on all power cords except one and I ended up insulating the chassis from the rack on each piece of gear except one in order to obtain a zero noise floor.
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Old 16th May 2020, 12:09 PM   #9
Burnedfingers is offline Burnedfingers  United States
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Quote:
Originally Posted by 6A3sUMMER View Post
There are some houses that have two-wire mains power outlets wired incorrectly,
Hot and Neutral are reversed. Who knew that? (someone was shocked to find out!)

And there are some houses that have three-wire mains power outlets wired incorrectly.
That is why they manufacture those three-wire mains power outlet safety testers (with the glowing lamps).

There are some three-wire IEC power cords that have been incorrectly wired.

Test your amplifier, test your power cords, test your mains power outlets; and test your friends mains power outlets when you bring your amplifier over to his house.

Using a polarized plug that is incorrectly wired on an amplifier, can cause the chassis to be connected to HOT!

Know thy devices and mains outlets, etc.
Or . . . Know thy maker!
If you have purchased a home in say the last 10-15 years the home was inspected prior to the loan going thru and or occupancy. Testing was done in order to confirm proper wiring, operation of circuits and ground fault circuits.

With respect to wiring of amplifiers, power cords and such... that is a function a any cheap VOM meter available for $2 at Harbor Freight. A simple continuity or ohms test will reveal a problem.
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Old 16th May 2020, 05:05 PM   #10
6A3sUMMER is online now 6A3sUMMER  United States
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Burnedfingers,

A broad statement about power mains outlets in a home that was purchased in the last 10 to 15 years, may not apply to all cities, counties, and states in the US.
And it may not apply to all other countries outside the US, either.
This is an international forum.

But, my home is 43 years old, and it does comply with the latest power outlet electrical standards.

Safety First!

Last edited by 6A3sUMMER; 16th May 2020 at 05:09 PM.
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