Noise, hum and AC polarity

I've been having a problem with a specific component combination generating a hum in my computer room system. The hum was only present when the gain of the preamp was cranked WAY up, so it was something that i was able to live with. Of course, i had verified that the outlets were wired correctly and had followed all of the other "procedures" that one does in a similar situation. I had tried every combination of "hum reduction" known to man. Lifting this ground and leaving that one hooked up, floating all the grounds, floating all but one ground, using / not using a PLC ( Power Line Conditioner ), etc... Nothing seemed to work.

With all of my tinkering, I was able to narrow it down to an interaction between the DAC and my preamp. Only problem is that i don't want to loose or substitute either of them. With that in mind, i decided to try an old trick that i had initially overlooked when hooking this system up. I mention this simply because this "old trick" seems to have made a very noticeable difference in total system performance. With that in mind, i'm sure that a few others may not know about this or have forgotten about it or simply not wanted to bother. What reminded me about this was reading a book by Laura Dearborn entitled "Good Sound" and Martin DeWulf's writings in Bound for Sound mentioning the same subject. What i'm getting round to talking about is AC polarity.

As any of you with beloved "old" gear ( aka "boat anchors", "antiques", "fossils" ) may remember, many products used to have two pronged AC plugs. Most of these plugs were not polarized, meaning that they would fit into the wall receptacle in either direction. The product works fine either way, so many people have never paid attention to such things. Newer products now have polarized plugs and / or a third pin used for grounding. This makes it next to impossible ( or so one would think ) to improperly orient the plug in the wall socket.

Since i have four components in that system that have fixed power cords with two pin non-polarized plugs, i decided to see which polarization worked best. While i was at it, i decided to check all of the other components too, even though they all have grounded three prong plugs.

In order to do this, one has to isolate each component from the other ( remove all interconnects ) and measure the voltage on the chassis of each component. You do this by connecting the black lead of a multimeter to an electrical ground and the red lead to the chassis of the component. Touching a screw is the easiest way to do this since many components are painted, etc... The multimeter should be set to read at least 120 volts on the AC voltage scale. By "ground", i'm talking about the third pin on your wall outlet OR whatever you are using as a ground if you have a dedicated ground. Keep in mind that these directions are for U.S. residents that use 120 volts as an operating standard. If you are somewhere else or using a different voltage standard, make sure that your multimeter is adjusted to handle that amount of voltage. On top of all things, be careful and take your time when doing this.

What you are trying to achieve is the lowest voltage potential on the chassis. To achieve this, you have to take a reading with the power cord plugged in one way and then reverse the polarity of the plug in the wall and take another reading. Whichever reading is lowest, that would be the "most correct" orientation.

With a non polarized two prong cord, doing the above is easy. You can simply pull the plug and flip it around with no hassles. One polarity will give you a notably higher reading than the other polarity ( in most cases ). The one that gives you the lowest reading is the most desirable. Since you run the risk of hooking the non-polarized plug up the wrong way again if the unit ever gets disconnected from the wall, you might want to mark one side of the plug. You will have to use some type of code that you will remember and do it with something that is pretty permanent. Nail polish is the "marker" of choice around here. Another alternative would be to install a polarized plug and be done with it.

If you have a polarized two prong or grounded ( 3 pin ) plug, this becomes a little more difficult. Since most "cheater plugs" that are used to lift the ground are now polarized, i had to look for another way to get around this. What worked best for me was a little outlet adapter from the hardware store. This device plugs into a single grounded outlet and gives you three grounded outlets to work from. The key ingredient as to why this works well is that, even though it has a ground pin, the other two prongs are NOT polarized. As such, we can remove the ground pin and we are home free. It will still accept the grounded power cord that you are plugging into it, but you can now flip the 3 into 1 adapter around to reverse polarity at the wall. Once again, you are looking for the polarity with the lowest voltage reading on the chassis.

One might think that checking 3 pronged components as i did is "goofy", but i will explain why it isn't:

1)Some components can be wired internally incorrectly from the factory.

2)Some power cords can be wired incorrectly

3)Some wall outlets can be wired incorrectly

Checking these possibilities out will either confirm or deny "proper operation". If you find something amiss, you can easily take the steps to correct it. I was able to measure 61 volts on the chassis of two components that had improper polarity, so it COULD become some type of a safety concern also. This is not to mention that it costs nothing ( if you already have a multimeter ) and will add to your "audio peace of mind".

As it turns out, all of my "three pronged" gear and cords were fine. As it turns out, I did have two components improperly polarized. One was my preamp and the other was a tuner. My other two prongers, which are a cassette deck and turntable, were fine. I corrected this, hooked everything back up and gave it a listen.

Initially, everything sounded somewhat thinner and sibilant. My first thoughts were "yuck". I let it play on for a while and ended up going to bed. Left the tuner on at low level just to keep things warmed up for when i woke up.

After climbing out of bed at a VERY leisurely hour : ), i popped in a disc and we were back to making magic. Whether it is my imagination or not, the sound seems more focused with greater detail and a noticeably lower noise floor. I am now obtaining results in the middle of the day comparable to what i was hearing in the middle of the night ( 1 or 2 AM ). That is the time that i've always gotten the best results / sonics out of any of my systems.

As to the hum situation, it has improved somewhat. The hum is still there, but it is lower in amplitude and comes in at an even higher gain setting. As such, the "old AC polarity trick" DID pay off in several aspects but was not a cure-all. Then again, few things in audio rarely are : )

I hope that someone else can put this info to use and is beneficial. Sean

PS... If you are going to do this, you obviously have to disconnect interconnects, power cords, etc... Make note of what cable goes where, in what direction, etc... BEFORE taking it all apart. Before re-installing everything, you might want to take the time to clean the various jacks involved with your favorite "snake oil". We can start a new thread on solvents / lubricants and techniques later : ) This would also be a good time to CAREFULLY lay out your cords so that the signal wires are not near the power cables, etc... if you have not done so previously.
Bravo! A great post, Sean, thank you.
Sorry if I missed it in your post, but everyone should also check the polarity of their wall plugs. Don't assume that the folks who wire your house installed all your wall plugs correctly. Also check the ground while your at it. All hardware stores should stock an inexpensive polarity checker.
Sean, upon re-reading, I am not clear as to how you "flip" the polarity of the 3:1 hardware store adapter.
Sugar is right and thanks for bringing that up. Sometimes we forget that people are "joining the conversation" with little to no background on previous threads.

You can pick up an AC Polarity Tester at your local hardware store or even Rat Shack. These typically cost well under $10 and can verify if things are "right" to begin with. There is NOTHING involved with using these, as there are three colored LED's and a chart to show if the outlet is wired correctly. You simply plug it in and it works. If something is wired incorrectly, you need to correct that before doing any further testing of your system. After all, it is hard to work with a corrupt point of reference.

As to "flipping" the polarity of the 3 outlet to 1 adapter, you have to break off the ground lug. The one that i had used two same sized ( non polarized ) prongs. That is the key factor in making the adapter acceptable for this type of task, as you can now flip it around in the outlet going in either polarity. The "adapter" would then have your three prong grounded power cord plugged into it yet it would convert it to a two prong non-polarized plug when going into the wall. Hope this helps and clarifies the above. Sean
Strongly agree. Have done this for years. Have my two-prong plugs painted with a dab of red nail polish on what is the hot side when properly inserted. Only thing that always amazes me is how quickly many will insert a 39-cent adapter between their $1200 fat boy and the hospital grade outlet on the dedicated line while listening for differences in bi-wire jumpers. :)
As I 've said before, what the world needs is an audiophile-grade cheater plug.

But more seriously (folks), maybe we need AC cords that are easily changed, or some other simple, user-configurable option.
I'm amazed that you read 61 volts from ground to chassis. Heck, I might have to check my gear just out of curiosity now. Obviously this was your highest reading? What were you able to correct the voltage to by flipping the cord? Sounds to me like something is shorting out inside the component. One time I read 50 volts on a ceiling wire. I don't think I have to tell you I got a nice little jolt every time I touched it.
Yeah, that has me kind of worried too Glen. I'm thinking that some of the coupling caps from board ground to chassis ground are coupling just a "bit" too much. The two that were up that high are also older pieces of gear, so i bet more than a few cap's are WAY out of tolerance. I'm going to have to go through them part by part to see what is going on. The power amp in that system measured about 35 volts with the polarity reversed.

As it is, the voltage went from 60 - 61 volts with the polarity reversed down to about 14 volts. I had one piece that showed less than 1 volt when reversed and another that was less than 4 volts.

I can probably spend a fortune "upgrading" and replacing out of tolerance components on this system. Then again, i'm very happy with the performance overall, so adding even more transparency to it via higher quality parts may be worthwhile. Sean
Thanks for the ideas, a very informative post. I'll be trying it soon!
Sean, thanks for reminding us! You've practically repeated, what Enid Lumley told us some 30 years ago. She was thought to be nutty then, which she certainly wasn't. By the way, there used to be a Jap. product on the market, I think it was called the Nakamiki Direction Finder, which did for more money, what a simple voltmeter would do for you. I think I've got it stashed away somewhere, must go look for it and check my more time to chat now....cheers,
Thanks Sean - you've cleared up a mystery. Have heard the term "absolute polarity" - is that a different type or one and the same.
Grandpad - absolute polarity usually refers to signal phase, i.e. whether it is correct or inverted. See the recent posts, including my own, under amps/preamps titled "Question about inverting polarity".
Another good trick to know is filing. You can file down the wide prong of a polarized 2-prong plug so that both prongs are the same width & it will plug in either way. I've had to do this once...
Yes, i agree Detlof. Enid Lumley was WAY, WAY ahead of her time. I can go back and read some of her stuff today and STILL think that she's a nut. None the less, i respect what she has to say, as she has more than proven herself. Only problem is that, like most others on the cutting edge of any field, "only time will tell" who's right and who's a lunatic. Too bad she didn't stick around and ride it out. With a few more folks like her around, we'd have no use for HP and all of the other "false prophets" that have taken root. She was one of the few that really did try to be an "audio alchemist".

Grandpad, as to "absolute polarity", you should check out some of Clark Johnsen's writings. Personally, Clark and i share some common ideas and thoughts but not on this one. I think that there is SO much "phase" & "polarity" junk taking place in the recording, mixing, mastering procedures that it would be next to impossible to verify "absolute" anything. One would literally have to supervise and understand the entire process from beginning to end in order for a recording to not be "corrupted" in one way or another. Sean
I rebuilt the antique pole lamp next to my listening chair( has 3 regular sockets and a HUGE centeral one for a 100/200/300 bulb. I painted the bronze trim with gold leaf paint, spent $80 on a classy shade...and sometimes noticed that when I happened to touch it lightly while listening that my fingers would tingle! Thought it was part of the goosebump-factor from my reference system....
Since it has a vintage non-polarized plug, I thought I'd check it for lowest "chassis" voltage.
So I stuck the VTVM's negative in the polarized outlet ground, and gently touched the positive to the lamp post.
I quickly reversed the plug and saw 8 volts.
$3 at Home Depot got me an old-looking black rubber polarized Leviton. The +8 volts doesn't raise the goosebumps
as easily, though!
Hope you guys are all well. Ern
Hey Ern, you should have stuck that lamp outside in the winter. If kids stuck their tongue to the metal to see if they would "stick" or freeze to it, you could have always done them a favor and turned on the "defroster" : ) Sean
Bob honed his "filing skills" when he was trying to go through the bars at Joliet State Correctional Facility when trying to break out. He was temporarily incarcerated there with his brother, Jake. Most people don't know it, but Bob is actually the third ( and little known ) Blues Brother. While Jake & Elwood were working the crowd, Bob "Blues" was the one behind the scenes flipping the switches and working the PA system. That's how he learned all of the technical stuff that he talks about here. He simply changed his name to hide his affiliation. Otherwise, he'd have to take time out every day to personally sign and autograph every email that he sent out : ) Sean

PS... I'm glad that Bob and most others here have a good sense of humour : )
See Mike Vansevers thoughts at:
Sean, I tried your test on an old 1970s two wire cord and plug Marantz Receiver, With the plug inserted into the 120V outlet one way I measure around 5.7VAC. With the plug rotated 180 degrees I measured around 18VAC. Lowest reading being the correct plug orientation.

I have tried to test three newer two wire cord and plug componets, CDP, DVD, and a CDR. Being the case on the units are floating, no equipment ground, I did the test from earth ground to the ground of the RCA connectors on the back of the units. I could not get a voltage reading. What did I do wrong.

Do the test the same way you did the first one and you will get your readings.
OK.......I did not read all of the repsonses, and not in any detail.

In short: There are VERY small leakage currents associated with the power transformers. It has to do with the winding polarity. That is why if you reverse them, you can measure and/or hear a difference.

If you go to Jensen Transformer's site, they have a very good paper there that explains this in more technical terms. May be too technical for most, but a good read anyway.

Also explains why noise filters that use a cap from either side of the line to ground are a bad idea. Use medical grade filters, if you must use filters.

Yes, after reading it, you may be more inclined to use coupling transformers. It worked on me. (The original text appeared in EDN about 10-15 years ago.)
If you go to Jensen Transformer's site, they have a very good paper there that explains this in more technical terms. May be too technical for most, but a good read anyway.

Great info.
Thanks for the post My vintage tuner happened to be oriented properly already. 1.1 volts versus 16v the other way. Experienced some disappointment that I didn't get a cheap improvement, ha! Someone may have already mentioned this but in case not make sure you turn off all your gear even though you disconnected the particular component being tested. Unplugging and plugging in your unit being tested can cause problems with anything on the same line which will manifest itself at the speakers. Just one thing though. Uh Sean you have my highest respect but er um red nail polish. I've got some red paint? Never mind. Don't wanna know.
Charles Hansen posted this on AA.
This is a great thread I have come back a couple of times to. Yesterday I checked this again, after making new power lines, duplex boxes, new duplexes, and new DIY power cords for my amp and pre. WTF!!!! What's wrong???

Lamm LL2 pre: 120V, and 100V after reversing polarity! This, of course, is ground to chassis with a lifted ground and ICs disconnected.
McIntosh MC275 amp: 85V and 60V after reversing polarity! This same amp had given me 4.4V and 2.4V in the past (glad I kept the notes). Weird.

Note we have 220V at home here. In case you are wondering if the volt meter was screwed up or wrongly set, it did measure 220V when checking + vs -, and + vs. ground.
After the ICs were punt back in place those readings all went to zero.

I get no hum, no hizz. I'm very surprised.

what could be wrong??? Seems hazardous.
Disconnecting ground (third prong) is very dangerous since device was designed to operate with ground present (different design). Reversing HOT and NEUTRAL when unit is not designed for that is also dangerous. It might also, in case of failure, create fire hazard since internal fuse will be on the NEUTRAL instead of HOT. 61V that you measure is leakage voltage that is not present when case is grounded. Get Jensen coupling transformers per Ar_t advice.

I'm surprised that you advertise making dangerous changes.
Read here:

Safety issue might be remedied (still not best solution) with GFCI outlet.