AC cord on vintage amp

[KEW]

My 30 year old Sansui AU-717 is in the shop for an overhaul. The guy is mainly cleaning off a glue that was used which becomes acidic and damages components causing failures and replacing any caps that are leaking or that have been in contact with the glue.

One of the options he suggested was installing an IEC connector for the AC cord. I can't see spending much money on that but I am thinking about simply replacing the current cord with a slightly better one myself. The original cable is 18AWG.
So my questions:

1) Could I expect to realize any benefit in performance? - I am considering de-soldering the current cord and replacing it with, say, a simple 14AWG cable. The Amp is rated at 85 Watts X 2. It has two outlets on the back. Only one will be used (for a Sansui TU-717 tuner).

2) Does polarity matter? - The plug is non grounded and predates modern plugs which have the larger blade on one side to force correct polarity. The fellow working on my amp says it will run either way, but it is better to use correct polarity (the cord does has a white stripe down the positive wire). Is he right?

Thanks,
Kurt

[highfigh]

My 30 year old Sansui AU-717 is in the shop for an overhaul. The guy is mainly cleaning off a glue that was used which becomes acidic and damages components causing failures and replacing any caps that are leaking or that have been in contact with the glue.

One of the options he suggested was installing an IEC connector for the AC cord. I can't see spending much money on that but I am thinking about simply replacing the current cord with a slightly better one myself. The original cable is 18AWG.
So my questions:

1) Could I expect to realize any benefit in performance? - I am considering de-soldering the current cord and replacing it with, say, a simple 14AWG cable. The Amp is rated at 85 Watts X 2. It has two outlets on the back. Only one will be used (for a Sansui TU-717 tuner).

2) Does polarity matter? - The plug is non grounded and predates modern plugs which have the larger blade on one side to force correct polarity. The fellow working on my amp says it will run either way, but it is better to use correct polarity (the cord does has a white stripe down the positive wire). Is he right?

Thanks,
Kurt

That Sansui may have a polarized plug already and you won't gain anything by replacing it. If you look at the original plug, one tab is probably wider than the other. A stripe means nothing- it's whether the plug is polarized, whether the design calls for a polarized plug and whether the polarized plug has the small tab connected to what needs to be the hot conductor. The tuner won't care and the chassis isn't grounded. The power transformer doesn't care, either.

[KEW]

Thanks highfigh!

The plug is definitely not polarized (nor are the outlets on the back of the amp). That is what I was attempting to say when I wrote "The plug is non grounded and predates modern plugs which have the larger blade on one side to force correct polarity."

So, if I follow, 18 AWG is fine.

Are you saying switching to a polarized plug would be worthwhile? Or that you are not sure on that point?

Thanks,
Kurt

[jonnythan]

Switching to a polarized plug does nothing for you.

There's nothing wrong with replacing an old power cord. I probably would, since it's so easy and already in the shop. Wouldn't bother spending the extra money to put an IEC connector on it though.

[highfigh]

Thanks highfigh!

The plug is definitely not polarized (nor are the outlets on the back of the amp). That is what I was attempting to say when I wrote "The plug is non grounded and predates modern plugs which have the larger blade on one side to force correct polarity."

So, if I follow, 18 AWG is fine.

Are you saying switching to a polarized plug would be worthwhile? Or that you are not sure on that point?

Thanks,
Kurt

I have audio equipment from the same vintage and unless the cord is cracked, spliced or damaged in some other way, I wouldn't bother. If it's 85W/ch, whatever is on it will be fine. The transformer has two wires going to the primary winding- one goes to hot and the other to neutral. There's no wrong way to connect them and the non-polarized plug is there because it just doesn't matter.

"It just doesn't matter" should be our mantra for a lot of things concerning audio and video.

[KEW]

Good to know!
Thanks!
If and when I find a good cord off of an old hair dryer, etc, destined for the trash, I might just go ahead with it since it'd be free, but based on this info, I'll wait until the cord finds me (rather than actively hunting for one).

[Johnny2Bad]

" ... Switching to a polarized plug does nothing for you. ..."

That will be true only if the Sansui uses a double-pole AC switch. I would expect it does, but you should have your service tech confirm it.

Assuming your home is properly wired (not always a safe assumption) the polarized plug insures that the hot and neutral wires are connected properly to the internal wiring of the amp (or home appliance).

With many more modern devices, the AC switch operates on the hot side of the unit only, and that is a normal way to build electronics and appliances today. The polarized plug insures the hot leg is connected across the unit's power switch (if the home is properly wired).

If it were to operate on the neutral leg, the device could be switched "off" and still have live wiring internally, creating a safety hazard if you were working on the amp or if there was a short of some kind, and it also has the potential of starting a fire if plugged into the wall but turned off.

Have your tech check and make sure the Sansui has a double-pole power switch. If it does not, the polarized plug is highly recommended.

I don't know if these safety issues also exist with the AC fuse, which normally is across only one leg of the AC supply, but they might be, and if so, again a polarized plug is the answer.

There is an advantage of a non-polarized plug on audio equipment; you can swap the AC plug by turning it 180 degrees and plugging it back in to the AC socket. This sometimes helps with issues regarding AC hum. I would not expect an integrated amp to have issues that way, but you never know. If you don't, then it's probably not important to retain the non-polarized plug.

A replacement AC cable and moulded plug is a relatively cheap part; we're talking like $3 here, assuming you get it from a "real" electronics parts supply store (eg DigiKey). There is no need to go with a boutique part on this particular unit; a regular UL listed replacement cord is fine. There is not much cost penalty in using a 16 or 14 GA version; I would personally avoid an 18GA cable on any unit that does amplification, but if you want, there is nothing stopping you from replacing it with the same gauge cable it came with.

The 3-wire IEC cable/connector, or simply a hard-wired 3-prong cable, offer some benefits regarding reducing AC noise, especially when other cables are near it (closer than 6") and parallel for any length, because it will be spiral wound. The straight parallel twin AC cord is somewhat more susceptible to introducing hum. Again, if this isn't a problem now, it's not worth panicking over, but there might be an improvement in system noise with the 3-conductor cord.

[highfigh]

" ... Switching to a polarized plug does nothing for you. ..."

That will be true only if the Sansui uses a double-pole AC switch. I would expect it does, but you should have your service tech confirm it.

Assuming your home is properly wired (not always a safe assumption) the polarized plug insures that the hot and neutral wires are connected properly to the internal wiring of the amp (or home appliance).

With many more modern devices, the AC switch operates on the hot side of the unit only, and that is a normal way to build electronics and appliances today. The polarized plug insures the hot leg is connected across the unit's power switch (if the home is properly wired).

If it were to operate on the neutral leg, the device could be switched "off" and still have live wiring internally, creating a safety hazard if you were working on the amp or if there was a short of some kind, and it also has the potential of starting a fire if plugged into the wall but turned off.

Have your tech check and make sure the Sansui has a double-pole power switch. If it does not, the polarized plug is highly recommended.

I don't know if these safety issues also exist with the AC fuse, which normally is across only one leg of the AC supply, but they might be, and if so, again a polarized plug is the answer.

There is an advantage of a non-polarized plug on audio equipment; you can swap the AC plug by turning it 180 degrees and plugging it back in to the AC socket. This sometimes helps with issues regarding AC hum. I would not expect an integrated amp to have issues that way, but you never know. If you don't, then it's probably not important to retain the non-polarized plug.

A replacement AC cable and moulded plug is a relatively cheap part; we're talking like $3 here, assuming you get it from a "real" electronics parts supply store (eg DigiKey). There is no need to go with a boutique part on this particular unit; a regular UL listed replacement cord is fine. There is not much cost penalty in using a 16 or 14 GA version; I would personally avoid an 18GA cable on any unit that does amplification, but if you want, there is nothing stopping you from replacing it with the same gauge cable it came with.

The 3-wire IEC cable/connector, or simply a hard-wired 3-prong cable, offer some benefits regarding reducing AC noise, especially when other cables are near it (closer than 6") and parallel for any length, because it will be spiral wound. The straight parallel twin AC cord is somewhat more susceptible to introducing hum. Again, if this isn't a problem now, it's not worth panicking over, but there might be an improvement in system noise with the 3-conductor cord.

I agree with the comments about the double pole switch and given the vintage of the amp in this thread, it probably is, since the plug isn't polarized and the dangers of switching the neutral have been known for a long time but the part about the parallel vs slightly twisted power cord is doubtful. The twist rate isn't sufficient to cause common-mode noise rejection and there's a lot of really good equipment out there with zip cord power cables that have great A/N ratio. My integrated amp is rated at 105dB and it's not twisted or grounded, but it it polarized.

If the audio cables are bundled with the power cord, all bets are off, anyway but the noise won't come in through the power cord unless a really strong magnetic field is very close and even then, the power supply will remove it.

[Johnny2Bad]

I agree with the comments about the double pole switch and given the vintage of the amp in this thread, it probably is, since the plug isn't polarized and the dangers of switching the neutral have been known for a long time but the part about the parallel vs slightly twisted power cord is doubtful. The twist rate isn't sufficient to cause common-mode noise rejection and there's a lot of really good equipment out there with zip cord power cables that have great A/N ratio. My integrated amp is rated at 105dB and it's not twisted or grounded, but it it polarized.

If the audio cables are bundled with the power cord, all bets are off, anyway but the noise won't come in through the power cord unless a really strong magnetic field is very close and even then, the power supply will remove it.

But the power supply is the source of the magnetic field; there is a field running parallel to the cord that is easily measured several inches from the cord, or your home wiring, and the power transformer emits an electromagnetic field. It's controlled, not removed, by shielding. The power supply cannot remove it; it runs on it. Filtering in the audio or video circuitry may attempt to remove it, but not inducing it in the first place is the first line of defense.

Unfortunately, there is more than one kind of noise that can be introduced in equipment. Common mode rejection is one means to reduce a certain kind of noise; it is not the only form of noise nor the only method to control noise.

Spiral wound construction and twisted wire are well established means to reduce interference between cables or internal wiring, and AC cords are available in a fully shielded form.

If cables carrying audio or video signals are within roughly 8" of an AC cord, there will be an electromagnetic field induced in that signal-carrying cable. It's minimized by avoiding parallel runs within that distance, and crossing, if necessary, at right angles, like a cross + instead of side-by-side =

The 8" value is just a practical limit, it's often necessary, due to practical issues, to be closer, and the appropriate distance depends on the strength of the AC field (how much power is being carried) and the level in the signal cable ... a turntable signal cable will be much more susceptible than a line level cable, for example. But, as a rule, try to get as much distance as you can.

You can also attempt to reduce the strength of that AC field. Spiral winding is simply a means to avoid that parallel construction so that the chances of interference are reduced somewhat.

None of this is exotic or expensive, or relies on anything beyond basic electronic theory, taught to every student for the last 60 years. For example, you can buy fully shielded IEC power cords at retail for $5. I know of no 3-conductor IEC-rated cord that is not spiral wound. TEK Cable (armored cable for running power outdoors or in wet locations) is spiral wound. Extension cords larger than 18GA are spiral wound. Why would that be, do you suppose? Spiral construction requires more copper per foot of cable than parallel ... is the entire planet wasting money for no reason, or is there a point to that method?

Of course, you can buy poorly constructed cords for the same price, or more. In order to make a good consumer choice, you should be aware of the differences ... it does not cost any more to buy the suitably constructed cable.

Also, the only reason this amplifier got away with an 18GA cable to begin with, is because the switched and unswitched AC outlets it has will have a maximum wattage rating printed on the back panel that are fairly low. It's easy to exceed those ratings, and things will definitely "work", but safety will be compromised if you do. A more robust power cable will mitigate that issue somewhat.

I'm sure we both agree that he does not need to replace the AC cable with anything beyond what is already installed, with the condition that the polarization issue be confirmed with regard to the amp's power switch, and the wattage rating is carefully followed for other AC equipment you may plug into the amp's accessory sockets.

But certainly there are good reasons that do not rely on "snake oil" to consider what your options are at this stage, since work is being done anyway, and there is no reason to choose poorly when soundly constructed options exist and cost essentially the same.

[highfigh]

But the power supply is the source of the magnetic field; there is a field running parallel to the cord that is easily measured several inches from the cord, or your home wiring, and the power transformer emits an electromagnetic field. It's controlled, not removed, by shielding. The power supply cannot remove it; it runs on it. Filtering in the audio or video circuitry may attempt to remove it, but not inducing it in the first place is the first line of defense.

Unfortunately, there is more than one kind of noise that can be introduced in equipment. Common mode rejection is one means to reduce a certain kind of noise; it is not the only form of noise nor the only method to control noise.

Spiral wound construction and twisted wire are well established means to reduce interference between cables or internal wiring, and AC cords are available in a fully shielded form.

If cables carrying audio or video signals are within roughly 8" of an AC cord, there will be an electromagnetic field induced in that signal-carrying cable. It's minimized by avoiding parallel runs within that distance, and crossing, if necessary, at right angles, like a cross + instead of side-by-side =

The 8" value is just a practical limit, it's often necessary, due to practical issues, to be closer, and the appropriate distance depends on the strength of the AC field (how much power is being carried) and the level in the signal cable ... a turntable signal cable will be much more susceptible than a line level cable, for example. But, as a rule, try to get as much distance as you can.

You can also attempt to reduce the strength of that AC field. Spiral winding is simply a means to avoid that parallel construction so that the chances of interference are reduced somewhat.

None of this is exotic or expensive, or relies on anything beyond basic electronic theory, taught to every student for the last 60 years. For example, you can buy fully shielded IEC power cords at retail for $5. I know of no 3-conductor IEC-rated cord that is not spiral wound. TEK Cable (armored cable for running power outdoors or in wet locations) is spiral wound. Extension cords larger than 18GA are spiral wound. Why would that be, do you suppose? Spiral construction requires more copper per foot of cable than parallel ... is the entire planet wasting money for no reason, or is there a point to that method?

Of course, you can buy poorly constructed cords for the same price, or more. In order to make a good consumer choice, you should be aware of the differences ... it does not cost any more to buy the suitably constructed cable.

Also, the only reason this amplifier got away with an 18GA cable to begin with, is because the switched and unswitched AC outlets it has will have a maximum wattage rating printed on the back panel that are fairly low. It's easy to exceed those ratings, and things will definitely "work", but safety will be compromised if you do. A more robust power cable will mitigate that issue somewhat.

I'm sure we both agree that he does not need to replace the AC cable with anything beyond what is already installed, with the condition that the polarization issue be confirmed with regard to the amp's power switch, and the wattage rating is carefully followed for other AC equipment you may plug into the amp's accessory sockets.

But certainly there are good reasons that do not rely on "snake oil" to consider what your options are at this stage, since work is being done anyway, and there is no reason to choose poorly when soundly constructed options exist and cost essentially the same.

Almost nothing in consumer electronics had a spiral wound cord until fairly recently and it all worked fine. The reason they wind the spiral is that with three conductors, round is more convenient than three conductors laying side-by-side and since extension cords were already being made, it only required a different ferrule or the IEC receptacle and plug to make this a possibility on consumer electronics. We know current flow creates a field but by having two conductors adjacent and parallel, it's minimized. The transformer doesn't do much for the added noise but the filter caps do if they're sized correctly. The induced voltage (EMI) can be a problem if it's from an extremely strong field, though, if it can increase/decrease the amplitude but the transformer uses the field its windings creates so no, it obviously can't be eliminated in that or we wouldn't be able to have high and low B+ voltages as cheaply.

I'm not sure this Sansui has an 18 gs power cord but if it does, Sansui was walking on the edge of 'adequate' and 'not quite enough'. My 30W/ch Sony integrated amp's cord was at least 16ga. If it's 18ga, I would probably change it, but I would look at the markings first.

Also, there's really no reason to run audio/Video cabling parallel to the power cords and intelligent system design/cable layout minimizes this, partly by avoiding most intersections and by crossing at right angles.