[Steve NJ]

Dear Roger,
 
Thank you for taking your very valuable time the other day, July 17, 2007, to help me and teach me, to walk me through how to use my volt meter to find the hum problem with my RM-10.  You were very pleasant and congenial, and spent over two and a half hours with me on the phone, between two phone calls, as you had me make up, and I forget what you called them, but they're two RCA plugs not attached to each other, with a hot and a ground wire twisted together, and you told me to call you back once I had made them, and we picked up from there, and spoke for another two hours, and words simply can't express how impressed I was in that, and I truly, truly am grateful.
 
Helping me find the problem with the hum was like having Derrick Jeter, or insert name of your favorite player, teaching me how to hit a baseball.  But that's not half of it.  You took your time with me and we had a very pleasurable conversation; you answered my questions, and by the way, I've never spoken with or had a conversation with a guru in the audio industry like I had with you.  You taught me more about electronics in that two and a half hours than I've learned in the twenty some odd years of messing around with audio equipment.  I don't know why, but I never would have imagined Roger Modjeski taking his time to help solve a customer’s problem over the phone.  But there it is.
 
You know that I've had that RM-10 for over ten years now, maybe twelve, and I really never had a problem with it before.  I think that speaks volumes of the built quality of Music Reference equipment.  Again, the built quality isn't the half of it.  My amp sounds magical, especially since you told me how to bias it properly.  It's never sounded more musical.  And, if that were enough, two of the most respected and influential audio reviewers in the industry, Michael Fremer and Sam Tellig have published that their reference tube power amp is the Music Reference RM-200.  WOWWWW!!!!  That's saying a lot.  Could there possibly be a better endorsement than that?  I don’t think anyone could get a better endorsement than that; considering all of the great equipment these guys have reviewed over the years. 
 
Well, all I really wanted to say to you, Roger, was thank you, thank you, thank you.  And congratulations on designing and building one of the finest family of amplifiers in the industry.

Best regards,

Steve W.
NJ

[Roger A. Modjeski]

Steve,

Thanks for the kind words and taking the time to join AC to relate your experience. Keep tuned because the fun is just beginning. It is always a delight for a teacher to have such a good student. It's not often I find someone who can follow my pace.

Tell your friends about AC. This is the best forum I have found to share ideas and report results in a sane environment.

Roger

[Steve NJ]

Thank you, Roger, I truly appreciate your sentiment. 

I'm enjoying reading the different entries on the Audio Circle, Music Reference site.  There are a lot of good questions and answers going back and forth, and I look forward to reading, learning and participating.

Here's one that I've often wondered about.  I've always been told that when plugging in a power amp, the plug should be inverted; I've even cut off the ground prong so I didn't have to use a cheater.  How can we determine the polarity of any component in terms of which way the plug should go into the socket; such as with the volt meter; on what position should it be set, where do we put the black and red probes (careful now); what reading(s) determine(s) which way the plug should go,  etc....?

Thank you, Roger. 

Best regards,

Steve W.
NJ

[jman66]

Hi Steve,

Interesting question. I read in my RM-9 manual and also mentioned yesterday in a conversation with Roger, the power amp should be the only grounded device in the audio chain. All other devices should have their grounds lifted, making the amp the focal point for grounding, diminishing the potential for ground loops.


Jim in NJ...

[Steve NJ]

Thank you, Jim.

I appreciate your helpful reply.

Best regards,

Steve

[lowrider]

Interesting question. I read in my RM-9 manual and also mentioned yesterday in a conversation with Roger, the power amp should be the only grounded device in the audio chain. All other devices should have their grounds lifted, making the amp the focal point for grounding, diminishing the potential for ground loops.

I thought it should be the preamp, as everything is connected to it... 

[jman66]

I thought it should be the preamp, as everything is connected to it... 

I came across that perspective too, posted on another tube amp manufacturer's website.
Guess is comes down to whatever grounding scheme works for you.

[lowrider]

Changed, grounded amplifier instead of pre, the PCs are also different, didnt bother modifying them again, just switched...

Didnt compare properly, apparentely there is not a big difference in sound...

Roger, why do you recommend grounding the amplifier, not the pre... 

[Bill Baker]

Hello Steve and others. First I hope I am not intruding posting on Roger's forum but I only wanted to respond to a particular question that I think I can help with.

How can we determine the polarity of any component in terms of which way the plug should go into the socket; such as with the volt meter; on what position should it be set, where do we put the black and red probes (careful now); what reading(s) determine(s) which way the plug should go,  etc....?

 A few years back, Stereophile posted an article on this subject. I tried it years ago and it does (can) make a huge difference. I have copies of it that I can fax right away or if given a day or so, I can scan it and send it via an email. I am not sure if the copies have the date and issue number but I will check shortly and post for those who still have their collection of Sterophile mags laying around.

 The only recommendation I have is not using a cheater or cutting the ground off a power cord. If possible, the best route (after determining best polarity) is to build or buy a power cord with the correct orientation.

[Steve NJ]

Thank you, Bill, and all for your thoughtful replies.

Bill, if you'd forward that Stereophile article on polarity, I'd appreciate it.

Thanks again, all.

Steve

[Gordy]

Is this the article you were referring to Bill?  It's not from Stereophile but, MGD at Bound For Sound...

http://www.boundforsound.com/tweak.htm

[Bill Baker]

 Yes Gordy, that is the same thing only with a bit more rambling in between. I would recommend giving this a try. It really can make a significant difference in imaging and soundtaging as well as lowering the noise floor.

For sake of protection, I have copied the warning which should always be considered before any attempt is made to play with AC current.

but remember, by floating the ground you may be defeating the UL rating for the device and maybe even voiding the warranty, which could be disastrous if for some reason a fire results. Play it safe.

[Roger A. Modjeski]

Thanks for all your responses and discussing it amongst yourselves.  I hope we continue along those lines. There are some good questions here and rather than quote each one I will take the subject on as a whole. If I miss a point you particularly want to discuss please post it.

In the beginning, nothing was grounded. Not radios, not amplifiers, nothin. I cannot say when 3 prong outlets came into vogue. I didn't have them in the house I grew up in which was built in VA in 1956. None of the classic Marantz, Fisher, Harmon Kardon or Dynaco... etc, etc had them. Adding one to these may make a quiet system into a hummer.

I recommend grounding only the power amp for the simple reason that it has the largest power transformer in the system. If your preamp had the largest transformer then I would ground it and not the power amp. The reason is quite simple: Every power transformer has capacitance between primary and secondary. The larger the transformer, the larger the capacitance. This capacitance is returned to the chassis making it have enough AC voltage that you can feel it. A high impedance digital AC voltmeter can often read several hundred volts between an ungrounded chassis and ground. But, if all is well, there is no current behind that voltage (Thevenin can be applied here). Most DVM (digital volt meters) have 10 megohm impedance. When I do these tests I put a 1 meg resistor right across the input terminals. If your meter has ¾ inch spaced bananas you can put a 1 meg resistor on the screws of a double banana plug and insert it in parallel with your probes. If you have any of the recent Fluke meters you will have to cut off that pesky plastic that hides the metal part of the banana. I’ve cut them off all of mine. With the 1 meg resistor in place the reading should go down by a factor of 10 and now every volt is a microamp. I typically see under 100 microamps, which presents no danger, but you might get a tingle.

Now we can answer the question of plug polarity. The Stereophile article, which I am not sure I have ever seen and would love to read it should a copy get posted here, likely refers to the following  practice which many audiophiles became aware of in the late 70’s. The trick was to disconnect all amps, preamps, tuners, tape decks, etc from each other and from the wall plug. So you have everything out in front of you, nothing connected to anything else. Then you found a good ground, a water pipe if no 3rd pin was available, and put the AC meter between the ground and the chassis of each component starting with the power amp as it should be the highest. Then you plugged the amp in the wall, noted the voltage (current), rotated the plug 180 degrees and noted the voltage in that polarity. You would choose the lower figure and mark the plug accordingly. Then on to the preamp, then on to the signal sources finding the lower current polarity for each and noting that the readings were getting smaller as you progressed toward the sources. A tape deck might have 1/10 the current of a power amp. It is also possible to get voltages from chassis to ground greater than the 120 volt line when the meter is 10 megs.

Now that the stage is set we can answer the question properly. If all this technical and measurement talk leaves you cold I encourage to take in what you can. As your knowledge builds these things will become more obvious. Often two engineers (or people skilled in the field) can say all of what I am explaining here in a sentence or two. One day when Bruce DePalma (I’ve mentioned him in previous posts) said to me: “I called the cable company to complain that their signal was rather weak causing noise (snow) in my picture. I asked the engineer  “Hey, why don’t you just turn up the gain a bit and give me a little more signal? The cable engineer replied “cross modulation”. Bruce chuckled, I chuckled as that’s all we had to hear. That problem had never occurred to us. The unsaid part, that the cable engineer felt would me immediately understood from his one word answer, was that higher gain in the amplifiers would allow cable channels to interfere with each other causing greater problems than a little noise in the picture. End of story. I hope many of you may gather the knowledge necessary to have such conversations. I also hope you will find that talking amongst each other about these matters makes conversations like  “This capacitor made my system really wonderful, you just have to try it”. There’s really nothing to discuss in such an exchange is there? It’s just a preference like white or whole wheat bread.

Since almost everything we buy these days has a 3 pin plug (which I usually cut off) we have a new situation to contend with. We can’t rotate that plug. The person who advised Steve to cut off the pin, rotate the plug and, I assume, leave it flipped over,  makes no sense at all. That implies that EVERY grounded plug we have is backwards. If his trick does reduce the hum, it is because he eliminated the problem when he cut off the ground pin. One could confirm that by flipping the plug back to the way it was. Nowadays most gear has IEC power cords so you can take a cheap one and cut the ground pin for your experiments or use a ground lifter (cheater they are also called) to make your experiments.  I have a box of IEC cords from computers with all their ground pins cut off. I reach for them more often than a grounded one. I have over a dozen instruments on my bench all missing but one missing their ground pins (or never had them).  The one unit I left the ground pin on has that ground brought out to a front panel binding post so I can use it or not without having to fool with plugs. Many home theater amps have a “ground lift” switch. Lifting the ground via the switch is the same as floating it at the plug.

Something that is often overlooked is a tuner or TV that is connected to cable or a roof antenna. At Beveridge we had a rooftop antenna only 30 feet below some high voltage power lines. The 60 Hz coming down that cable was very strong.  TV cable running along with AC distribution can pick up very strong 60 cycle currents. Even if you take my advice and ground just the power amp you can have very loud hum even with the TV off and listening to CD.. The best way to cure this is a simple cable isolator. It’s basically a 1:1 isolation transformer for cable frequencies. In a pinch I’ve made one by taking two 300 ohm to 75 ohm transformers connecting the 300 ohm leads back to back leaving a 75 ohm input and output. Then you get double isolation but a little more signal loss. This hum often intrudes on all inputs as it finds its way to ground via whatever path is available. This offending cable current is there whether the TV is on or not. Whether it is plugged into the wall or not. But this hum is easy to find, just pull the TV audio cables out of the back of you preamp and the hum goes away. For a quick fix the other choice it to float all the grounds, but I advise against that because I have measured (and felt) some sizable voltages between TV cable and ground. Anyone ever get shocked hooking the coax to the tuner RF jack while holding the tuner? Don’t be standing barefoot on concrete when you fool with the TV cable either.

Here is why I contend the power amp and only the power amp should be grounded. Remember that we measured or through logic decided that the power amp has the largest AC (60 Hz) current to ground. The preamp less and the sources even less. If we ground the preamp and not the power amp that current has to flow through the interconnects to the preamp to find ground via the preamp power cord. That’s where the hum enters the system. The current causes a small voltage drop across the shield wire of the  interconnect which, to the power amp, looks just like the audio signal and gets amplified and gets sent to your speaker. Many years ago I had loaned a power amp to a speaker maker and he was having more than a little problem at the CES with hum. I walked in the room and heard it, looked at the plugs, saw the CD player (of all things) was grounded. From a hum point of view a CD player should not be grounded. Let it and the preamp find ground through the interconnects. If you still have hum due to these currents a heavy wire tied along the interconnect from chassis to chassis will help. The cable should be shielded. Some cables have this third wire and it should be at least 18 gauge; thicker for longer runs.

So far none of this is about loops. Often the problem is not a ground loop but chassis current’s finding their way to ground. When something electrical doesn’t work, I find most people say “there must be a short”. In actually, 9 times out of 10 when something won’t work it’s an open. In the same way, the audio community has made the term “ ground loop” as the catch-all for hum problems. It is often not the case. In a simple system with a CD player, preamp and power amp (all with ground pins) you might find that arbitrary grounding only the preamp reduces the hum considerably, you might as well find that the system is even more hum free if just the power amp is grounded. That is the logical choice.

After we kick this one around for a bit, we can get into balanced lines.

[lowrider]

Thanks Roger,

I had this problem first time with my AV, since then I have always lifted the ground from all but one component, in my system in Portugal one subwoofer is the only grounded, as I found more convenient to disconnect the ground in the wall sockets, except that one...

In my last system I use only one socket, and disconnected the ground on all cables, but one...

As for antenna cables, I was several times "eltrocuted" touching the boxes... 

In Portugal no hum from cable, but in Latvia yes, from satellite, so I choose not to connect the box and the DVD at the same time, have to manually disconnect the cable to switch source, and digital audio goes by optical cable, the problem is that when watching satellite, neither the TV nor the box are grounded, so bigger shocks... 

In Europe no problem rotating the plugs, I use the "NEL" method to check polarity, I know some gear has wrong polarity, but doing listening tests, I always either hear no difference, or the NEL worked and it sounds better that way...

[Steve NJ]

Thank you for your indepth reply, Roger, regarding my question of how to determine the polarity of  an audio component.  I 've read it through, but will need to study it thoroughly to make complete sense of it all.

Thanks again, Roger.

Best regards,

Steve W.
NJ

[Scottdazzle]

Roger,

A previous owner cut off the ground plug from my RM-9.  I would like it to be grounded as you recommend and every other component not.  Do you recommend replacing the stock cable with an IEC to accomplish this goal?  Is there a right way to do it?  Thanks for the amp and the advice.

Scott

[Roger A. Modjeski]

Scott,

Too bad he didn't read the manual. There really is no good place nor good reason to put on an IEC connector. Go to a hardware store, buy a 3 pin plug and put it on.  Cut off the old plug and you will see 3 wires. White is hot, black is neutral, green is ground.

Roger

[Scottdazzle]

Thank you! I will.