Bravo! A great post, Sean, thank you.
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.
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.
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