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.
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)
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)
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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.
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.
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
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
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!
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!
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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.
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.
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!
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!
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Ok,
Basically every U.S. home built in the last 10-15 years has been tested prior to sale for proper electrical wiring, grounds, and ground fault devices and therefore should be safe unless some idiot has gotten their hands into the wiring making changes. This very basic check does apply to all cities, counties, and states in the U.S. Its called an inspection and the normal charge for this service is in the neighborhood of $400-650. The inspection is mandatory, a termite or Ozone inspection is not mandatory. In addition most items in the home or concerning the home are tested. I just had my property in AZ inspected by its buyer and I had a property in Iowa inspected that I am purchasing. Its a lucrative business with inspectors inspecting 2 to three properties per day generating $1200-1800+ a day.
Today if you were to sell your 40+ year old home it would have to be inspected and the cost in most cases is born by the purchaser wishing to buy your property. In the case of FSBO (for sale by owner) the cost is born by the seller of the property. In the event that problems arose the seller is responsible for compliance and necessary repairs so the property will pass inspection.
About the only way out of this would be if you were to inherit a property without a lien on it. If a bank or credit union or other financial entity has their hands in the transaction there will be an inspection and this inspection insures that everything at the time of the inspection is normal and working.
Basically every U.S. home built in the last 10-15 years has been tested prior to sale for proper electrical wiring, grounds, and ground fault devices and therefore should be safe unless some idiot has gotten their hands into the wiring making changes. This very basic check does apply to all cities, counties, and states in the U.S. Its called an inspection and the normal charge for this service is in the neighborhood of $400-650. The inspection is mandatory, a termite or Ozone inspection is not mandatory. In addition most items in the home or concerning the home are tested. I just had my property in AZ inspected by its buyer and I had a property in Iowa inspected that I am purchasing. Its a lucrative business with inspectors inspecting 2 to three properties per day generating $1200-1800+ a day.
Today if you were to sell your 40+ year old home it would have to be inspected and the cost in most cases is born by the purchaser wishing to buy your property. In the case of FSBO (for sale by owner) the cost is born by the seller of the property. In the event that problems arose the seller is responsible for compliance and necessary repairs so the property will pass inspection.
About the only way out of this would be if you were to inherit a property without a lien on it. If a bank or credit union or other financial entity has their hands in the transaction there will be an inspection and this inspection insures that everything at the time of the inspection is normal and working.
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Old houses here in the Netherlands have two-terminal wall sockets everywhere except in the bathroom and kitchen and the plugs are symmetrical, so you never know which side is hot and which neutral. Three-pin plugs with safety earth fit in the two-terminal sockets, the earth terminal then simply doesn't get connected. Fortunately, ground fault interrupters (residual current devices) are used a lot, even in old Dutch houses.
Burnedfingers,
I am glad that you mentioned some idiot getting their hands on the wiring and making changes.
Incorrectly wired replacement of an outlet, because a shorted product smoked the correctly wired outlet.
Or, someone who purchases a "Hi Fi Specialty Outlet", installs it himself, and mis-wires it.
I have seen mis-wired 3-wire IEC power cords. You can not tell by "looking through" the molded wire and connectors.
Test everything, and trust nothing.
"If anything can go wrong, it will" - Murphy
I am glad that you mentioned some idiot getting their hands on the wiring and making changes.
Incorrectly wired replacement of an outlet, because a shorted product smoked the correctly wired outlet.
Or, someone who purchases a "Hi Fi Specialty Outlet", installs it himself, and mis-wires it.
I have seen mis-wired 3-wire IEC power cords. You can not tell by "looking through" the molded wire and connectors.
Test everything, and trust nothing.
"If anything can go wrong, it will" - Murphy
Since in many countries the polarity of the line and neutral are not fixed, and it is possible that even where the outlet does enforce polarity it may be incorrect, as Eli points out, then it is prudent to not make assumptions about polarity in the amp.
If the IEC plug that Eli was mis-wired had the earth wire incorrect, then that would be a big deal, but hopefully would blow the main fuse in the house.
Making use of the earth connection, by always converting 2 wire amps to 3 wire ones, is a mechanism to reduce the risk of using old electronics where safety related issues can occur in external equipment.
If the IEC plug that Eli was mis-wired had the earth wire incorrect, then that would be a big deal, but hopefully would blow the main fuse in the house.
Making use of the earth connection, by always converting 2 wire amps to 3 wire ones, is a mechanism to reduce the risk of using old electronics where safety related issues can occur in external equipment.
I absolutely like that.... "Test Everything and Trust Nothing"
That is exactly how I ran every service call I made before I retired. Basically I looked at the work ticket and then I asked the customer what their problem and concerns were. After doing that I tackled the problem. One has to approach any problem assuming nothing and starting at step one analyze the problem. Don't assume wiring is correct check it. Don't assume you have voltage check it. Don't assume polarity check it.
I had a service ticket one time where the customer of the business did his own wiring and I found the ceiling grid hot. This was just one of a number of things I encountered. It would seem that stupidy rules in a lot of cases.
Since you are doing this commercially, I would have thought it could be quite an attractive service to offer to the customer.
A garage I used to go to used to steam clean the engine as part of the work they did. They were doing it for themselves in the end (these were old 60's cars that used leaking oil running down the diff shaft as part of the rust proofing), but it seemed like a nice touch when collecting the car later.
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