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 <i>need to</i> 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 <i>need to</i> 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.

 

[Johnny2Bad]

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.

I'm not sure this Sansui has an 18 gs power cord but if it does ...

Yep ... almost nothing. Like my 1978 Bryston 2B, a whopping 50wpc amplifier. (If anyone remembers, Bryston would coil 2/3rds of the length to fit rackmounts better). LIke every serious power amplifier from the 1970's on. Or every TEAC, Technics (... Otari, MCI, Studer, ...) open reel recorder, dating back to the 60's at least. I could go on.

The IEC does not apply in the US or Canada; nor is it a set of regulations; it is a guideline document suggesting best practices in Europe, which is sometimes referenced in actual regulations. The NEC (US) and CSA (Canada) are law. Condition of power cords and replacement of power cords must comply with the NEC in the US. There are specific regulations regarding how power cords must be constructed, and how extension cords must be constructed, and they are most certainly not the same.

I've seen Sansui integrated amps of that series (AU-<i>n</i>1<i>n</i>) with 18GA,16GA and 14GA power cords. I once owned one, but it's long gone now, so I can't check for you. However, at the time, SPT-1 cord was allowable under the NEC for power cable ... if it's replaced with stranded two conductor cable, it must now meet SPT-2 at a minimum. The regulation refers to insulation thickness, so a 16GA SPT-1 cable may resemble 18GA SPT-2 if you just judge by the overall appearance; you would have to strip and examine the current carrying copper strands to know for sure what the gauge was.

I have no idea what you're trying to say with the rest of that post.

 

[highfigh]

Yep ... almost nothing. Like my 1978 Bryston 2B, a whopping 50wpc amplifier. (If anyone remembers, Bryston would coil 2/3rds of the length to fit rackmounts better). LIke every serious power amplifier from the 1970's on. Or every TEAC, Technics (... Otari, MCI, Studer, ...) open reel recorder, dating back to the 60's at least. I could go on.

The IEC does not apply in the US or Canada; nor is it a set of regulations; it is a guideline document suggesting best practices in Europe, which is sometimes referenced in actual regulations. The NEC (US) and CSA (Canada) are law. Condition of power cords and replacement of power cords must comply with the NEC in the US. There are specific regulations regarding how power cords must be constructed, and how extension cords must be constructed, and they are most certainly not the same.

I've seen Sansui integrated amps of that series (AU-<i>n</i>1<i>n</i>) with 18GA,16GA and 14GA power cords. I once owned one, but it's long gone now, so I can't check for you.

I have no idea what you're trying to say with the rest of that post.

I have a Conrad Johnson amp from the early '80s and it has a relatively heavy cord but it's only rated at 45W/ch and the fuse is 5V Slo-Blo. It's two-conductor and last time I talked with someone in their technical department, I asked about whether I should put a three-conductor on and he said it won't matter since the audio isn't at chassis potential. The plug is polarized, though.

I have to assume the manufacturers put IEC on everything now because they don't want to have one production line for IEC and another for non-IEC.

I was saying the fields around the power cord have minimal affect on sound and general performance unless they're extremely strong. It's the low voltage signals that are most easily altered.

 

[KEW]

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.

I used the markings on the cord to determine it was 18AWG.

 

[Johnny2Bad]

I have a Conrad Johnson amp from the early '80s and it has a relatively heavy cord but it's only rated at 45W/ch and the fuse is 5V Slo-Blo. It's two-conductor and last time I talked with someone in their technical department, I asked about whether I should put a three-conductor on and he said it won't matter since the audio isn't at chassis potential. The plug is polarized, though.

That unit would have been manufactured under somewhat more stringent requirements than the Sansui the OP was asking about. Prior to about mid-60's, there were virtually no safety regulation or requirements about stuff that was beyond the AC socket in the wall (ie appliances, audio equipment, etc).

More than 95% of those regulations were written since 1980, often the process for studying a new rule begins with the listing of names of those who died as a result of some safety deficiency.

The Sansui would have had to meet only the most minimal rules during it's time of manufacture.

I have to assume the manufacturers put IEC on everything now because they don't want to have one production line for IEC and another for non-IEC.

The IEC is not a regulatory body. Nothing is required to meet IEC standards, here or anywhere else. Sometimes an IEC standard is given as an example in the NEC code of what would meet the regulation, but there is no need to meet an IEC proposal to none the less be compliant with the actual regulating bodies.

In part it's because if it meets UL or CSA-US (for example) it may also meet IEC. For example, there is an IEC standard that describes the connector at the equipment side (not the AC plug side). Provided the cord meets other regulations that apply to the connector at the equipment side, the IEC connector is allowed. That should not be confused to mean all IEC compliant power cords would automatically meet UL or CSA-US; many would not.

When you read "IEC connector" they're referring to IEC 60320, which lists 13 types of connectors at the equipment side of the power cable.

However, it probably has something to do with impressing the consumer. Manufacturers like to stick compliance logos all over their gear, and talk about governing bodies as if they actually all were mandatory. ISO 9000-this and CE that; you see the CE logo on lots of stuff, for just one example.

But what is the requirement to certify as meeting CE standards (and use the logo)? There are none ... it is compliant if the manufacturer claims it is; the compliance procedure consists entirely on self-declaration by the manufacturer. Nothing more.

I was saying the fields around the power cord have minimal affect on sound and general performance unless they're extremely strong. It's the low voltage signals that are most easily altered.

And I was saying those low voltage signals are most easily affected by the power cord and the power transformer. You can achieve better results by both minimizing the susceptibility of the low voltage cables and also minimizing the emissions of the power cable and supply, than by doing one alone.

Thanks for clarifying that earlier post. We are not that far apart as it might have looked before.

 

[highfigh]

However, it probably has something to do with impressing the consumer. Manufacturers like to stick compliance logos all over their gear, and talk about governing bodies as if they actually all were mandatory. ISO 9000-this and CE that; you see the CE logo on lots of stuff, for just one example.

And I was saying those low voltage signals are most easily affected by the power cord and the power transformer. You can achieve better results by both minimizing the susceptibility of the low voltage cables and also minimizing the emissions of the power cable and supply, than by doing one alone.

Thanks for clarifying that earlier post. We are not that far apart as it might have looked before.

Like the Tom Waits song says, "The large print giveth and the small print taketh away". All of the acronyms, logos and initials that really say "We strive to "comply" with every "rule and regulation" that makes it possible for us to make you confused, give up all reasoning and pay us more for this product of dubious quality and if we happen to make it in a way that it meets safety requirements, that's cool " work very well. PArt of the reason products need to be made "idiot-proof" is that so many people who install electrical wiring are idiots, too. They don't follow code (like the nimrod who wired my garage) and just do things wrong (like my parents' friend who was an EE and wired their garage with a three-way switch that switched the neutral, making the aluminum siding hot when it alternated). Apparently, my family is a good attractor for bad electricians.

You're right- we're close, just wording it differently and the common theme here is that neither of us wants to be the load.

 

[KEW]

Okay, I just checked my Yamaha P7000S pro amp with 950WPC into 4 ohms from 20 - 20kHz at 0.1%THD, and although the cord is much heavier (better insulation?), it is 18AWG. There are no outlets and Yamaha extols the efficiency of this amp, which I am sure totally eclipses my Sansui; but is 18AWG really enough for the Yamaha?

 

[Johnny2Bad]

Okay, I just checked my Yamaha P7000S pro amp with 950WPC into 4 ohms from 20 - 20kHz at 0.1%THD, and although the cord is much heavier (better insulation?), it is 18AWG. There are no outlets and Yamaha extols the efficiency of this amp, which I am sure totally eclipses my Sansui; but is 18AWG really enough for the Yamaha?

That is not such a simple question to answer.

The specs you mention are dancing around the question but not actually nailing it. Plus, they are incomplete, so we can't actually reference "950 watts per channel" into something meaningful without more descriptors.

Just by way of example, if that's 950 watts into 4 ohms with one channel driven, it's one thing; if it's 950 watts into 4 ohms at 20~20,000 Hz, both channels driven, at x% THD, that's another (the latter spec will mean it probably draws more current from the AC supply). If it has a conventional power supply, it may be only 55% efficient; if it has a switching supply, it may be 90%+ efficient. The latter will require less current draw from the AC supply. And so on. (I can tell you the Sansui definitely has a conventional supply, and, without looking at the specs online, it sounds like the Yamaha has a switching supply).

The important one is the current draw in Watts (voltage is also an issue, but it's 120V in the US, mostly, for audio gear).

That must be listed on the unit near the AC cord. I think (don't quote me, but you could look it up) that if the current draw is somewhere around 350 watts or less it's OK with 18 GA. You should be able to read that by examining the unit; either embossed or on a sticker. It's supposed to be on every thing that plugs into a wall outlet.

You also want to see a certification lab mark; UL (an insurance industry certification; Underwriter's Laboratories) and CSA (a Government safety testing lab, Canada Standards Association) are good and are considered equivalent. There's more, but basically you don't need to worry about it much if one or more of those marks are present and you use the gear in the US or Canada.

Be aware that it's hardly unheard of for cheap imported goods to counterfeit the marks. More common with lamps and cheap consumer goods, but not unheard of with audio gear. Buy from trusted manufacturers if there is any doubt. It's also possible, but not exactly easy, to cross reference the number to see if that matches the unit, or if it exists at all.

Although I don't know of many actual cases, it's possible that if an amp burns your house down, and it isn't certified by one of those two, they can deny your insurance claim. For the whole house. Just so you know. That's where we extend the "buy from trusted manufacturers" to "get insurance from a decent company" that isn't bent on denying claims at all costs, if only because you don't want to have to settle for less or go to court.

Also, the unit will be certified based on the regulations in existence when it was made. It may not pass today's muster. Having said that, if it passed at some point in the past, it's still OK to use it today, assuming it's in good condition.

Oh, and How About Dem Saints! It's the first time in about a decade that a team I cheered for won. My rule is if my team doesn't make it, I cheer for the other conference.

 

[KEW]

Thanks!

That is not such a simple question to answer.

The specs you mention are dancing around the question but not actually nailing it. Plus, they are incomplete, so we can't actually reference "950 watts per channel" into something meaningful without more descriptors.

Just by way of example, if that's 950 watts into 4 ohms with one channel driven, it's one thing; if it's 950 watts into 4 ohms at 20~20,000 Hz, both channels driven, at x% THD, that's another (the latter spec will mean it probably draws more current from the AC supply). If it has a conventional power supply, it may be only 55% efficient; if it has a switching supply, it may be 90%+ efficient. The latter will require less current draw from the AC supply. And so on. (I can tell you the Sansui definitely has a conventional supply, and, without looking at the specs online, it sounds like the Yamaha has a switching supply).

Actually, I did give the specs with everything you mention except "both channels driven". The Yamaha spec say in stereo mode, so I would presume that means both channels driven.
Yamaha literature states:
EEEngine (Energy Efficient Engine) Technology makes more efficient use of AC power by reducing power consumption and heat generation without sacrificing output power or sound quality. When power requirements are low, the system uses a highly efficient current buffer to transparently switch input power on and off as needed. As power requirements increase, an independently responding auxiliary power line supplies additional power as required. Output isn't compromised because the auxiliary power line is driven by the power supply voltage which maintains maximum output to the speaker load.

I think you are right - that seems like a gussied-up way of saying it has a switching supply.

The important one is the current draw in Watts (voltage is also an issue, but it's 120V in the US, mostly, for audio gear).

That must be listed on the unit near the AC cord. I think (don't quote me, but you could look it up) that if the current draw is somewhere around 350 watts or less it's OK with 18 GA. You should be able to read that by examining the unit; either embossed or on a sticker. It's supposed to be on every thing that plugs into a wall outlet.

I couldn't find it on the back of the unit! However, if I interpret it correctly 650Watts would be the answer. The spec sheet is here:
http://www.yamahaproaudio.com/products/power_amps/p7000s/specifications.html
http://www.yamahaproaudio.com/downloads/documents/data/utilities_data/p_heatspec.pdf

You also want to see a certification lab mark; UL (an insurance industry certification; Underwriter's Laboratories) and CSA (a Government safety testing lab, Canada Standards Association) are good and are considered equivalent. There's more, but basically you don't need to worry about it much if one or more of those marks are present and you use the gear in the US or Canada.

Be aware that it's hardly unheard of for cheap imported goods to counterfeit the marks. More common with lamps and cheap consumer goods, but not unheard of with audio gear. Buy from trusted manufacturers if there is any doubt. It's also possible, but not exactly easy, to cross reference the number to see if that matches the unit, or if it exists at all.

Although I don't know of many actual cases, it's possible that if an amp burns your house down, and it isn't certified by one of those two, they can deny your insurance claim. For the whole house. Just so you know. That's where we extend the "buy from trusted manufacturers" to "get insurance from a decent company" that isn't bent on denying claims at all costs, if only because you don't want to have to settle for less or go to court.

Also, the unit will be certified based on the regulations in existence when it was made. It may not pass today's muster. Having said that, if it passed at some point in the past, it's still OK to use it today, assuming it's in good condition.

My Yamaha amp seems to be running under the radar. It has no markings! The cord is marked UL and CSA, but I'm not sure if that applies to the generic cord or applies to the specific amplifier. Could the markings be inside? I wonder if pro-amps are somehow different? Yamaha is a pretty established player not to be meeting industry norms!

Oh, and How About Dem Saints! It's the first time in about a decade that a team I cheered for won. My rule is if my team doesn't make it, I cheer for the other conference.

I was pulling for the Saints (mainly because they were losing at 10-0 when I tuned in) but mainly just enjoyed a good game with a great comeback!

 

[Johnny2Bad]

The markings must be on the outside of the unit.

This is not a home hifi amplifier. Current draw can be as high as 21 Amps from a 120V line for the P7000S, when operating at continuous 1/3 power with music signals into 4 ohms (what Yamaha calls "significant clipping"). No home AC line can deliver that much power, at least without tripping a breaker (good) or starting a fire (bad).

Under "normal" use (ie "occasional clipping" according to Yamaha, or about 1/8 continuous power), draw is around 10A or less.

The AC power supply ratings are usually in watts, but they can be in amps. Amps x Volts = watts, so 10A x 120V = 1200 watts.

That 650 Watts from the link is not the current draw, its the thermal dissipation value.

The unit does not appear to have any power draw regulation so it basically just sucks up whatever it needs, until the job is done or it gets too hot and goes into thermal protection (90C or above).

You have to download a pdf to get this power info.

As for power output, this is rated in terms of sound reinforcement use, not what we would expect in a hifi amp. For example, rated power into 8 ohms, 20~20K, 0.1% THD+N is listed as 700 watts. Yet, all specifications are indicated at "half power", including Power Bandwith, THD+N, IMD, etc. One wonders what the true clipping level with continuous signal would be.

This is like a stadium facility amp or sound reinforcement amp, designed to supply large sound pressure levels at live events, using a version of Class D amplification (whenever you see any Class other than A, B, AB, C, or D, it's a manufacturer's own name for one of the above; in this case Yamaha calls it "EEEngine").

I would probably not use such an amp in a hifi setting, myself. Broadly speaking, they do not always sound that good compared to a true hifi amp. It's different when you're creating the sound versus reproducing it ... there are no sonic errors in music creation ... it is what it is. The home amp has the job of accurately recreating whatever "it" was.

But, there's no harm in trying it. A Musician I know says the Yamaha P7000S and it's sisters are not recommended for sub use; apparently a little weak in the low end at high power. He uses them for top end only. They are popular budget amps for clubs, discos, churches, and bands, he tells me.