Please explain how/why a "cheater" plug adapter functions

[LarryC]

I had a bad 60-Hz hum (NOT a buzz) from plugging a pair of Mark Levinson ML-2 monoblocs into either the same or separate circuits that could be solved only by using a cheater plug on one of the ML-2's.  I don't recall if the hum was from one amp or both.

 

It was not possible to solve it any other way, and there was no way I or anyone else would be dabbling or checking out or revising those amps' circuitry.  No one could explain it, except to say "ground loop" without any real explanation.

 

I had 20-amp isolated ground circuitry installed on those outlets, but to no benefit on the hum.  I had to live with the single cheater plug permanently.  A hum-X would have been interesting to try. 

Edited November 8, 2015 by LarryC

[westom]

I had a bad 60-Hz hum (NOT a buzz) from plugging a pair of Mark Levinson ML-2 monoblocs into either the same or separate circuits that could be solved only by using a cheater plug on one of the ML-2's.  

 

Which means you completely ignored this description of what a hum is, how to find it, and what 'curing symptoms' is.

[LarryC]

Which means you completely ignored this description of what a hum is, how to find it, and what 'curing symptoms' is.

I only said no one could explain it to me, meaning the smattering of upper-level techs in the industry that I spoke to.  As I said, I wasn't about to mess with internal circuitry that I didn't know a thing about in expensive amplifiers like the ML-2.  I also wasn't about to make a research project of it like you did, but rather just asked around about realistic, simple explanations and fixes that would go to the heart of the issue.

 

Your citation would have been of no use or help to me -- so why shouldn't I have "ignored" it, if I wasn't delving into that kind of esoterica that wouldn't help me solve the problem?

Edited November 8, 2015 by LarryC

[Shiva]

 

http://www.lowes.com/pd_145257-33536-C629171___?productId=1135905&pl=1&Ntt=circuit+breaker+power+cord

 

I had a similar issue with a power amp and adding  a cheater plug also stopped the hum. Through some reading I bought the above power cord that I plugged the cheater plug into for some added safety.   For those in the know does this not make the ungrounded amp safe from possible shocks.g

Nope.

 

Lol, your answer was a bit terse.  Care to elaborate.  If there is a short of some kind in the amp that could cause a shock, would that not trip the circuit breaker in the power cord and cut the power. 

[westom]

As I said, I wasn't about to mess with internal circuitry that I didn't know a thing about in expensive amplifiers like the ML-2.  I also wasn't about to make a research project of it like you did, but rather just asked around about realistic, simple explanations and fixes that would go to the heart of the issue.

 

Simple solution was posted.  Nobody said or even implied messing with internal circuitry.  Nobody said anything about making it a research project.  Both examples of not reading what was posted.  Simple explanation went right to the relevant question. What is the loop?  Then defined is a part to return for warranty repair. 

 

Living "with the single cheater plug permanently" is obviously a worst possible solution.  An example of curing symptoms and of arrogance.  Problem was explained.  A layman knows compromising human safety is not acceptable.

 

Isolated ground circuitry is irrelevant to the problem and not a solution. Upper-level techs would know the concept in these paragrasphs.  Why did they not?  Or maybe you assumed what they did not say; as you did with a previous post.

 

Your permanent solution was unacceptable and unnecessary.

Edited November 8, 2015 by westom

[mike stehr]

Here's Miss Beasley...obsolete and unacceptable in today's society.

 

[Travis In Austin]

I had a bad 60-Hz hum (NOT a buzz) from plugging a pair of Mark Levinson ML-2 monoblocs into either the same or separate circuits that could be solved only by using a cheater plug on one of the ML-2's.

Which means you completely ignored this description of what a hum is, how to find it, and what 'curing symptoms' is.

So are you saying a hum or a buzz is only caused by a particular piece of equipment having an internal problem?

[xxJPMxx]

So are you saying a hum or a buzz is only caused by a particular piece of equipment having an internal problem?

 

No. I would refrain from taking westoms advice.

 

 

 

The tube amp's transformer has a large stray magnetic field most likely being induced into the chassis.

 

It is not uncommon to have an induced voltage of perhaps 1V RMS between the earth connections of power outlets that are wired separately back to the electrical panel. This small voltage, with a total resistance of perhaps 0.5 Ohm, will cause a loop current of 5 Amps, all of which flows in the shield of the interconnect. This is sufficient to cause a voltage difference across the interconnect, which the amplifier cannot differentiate from the wanted signal. The earth loop will inject a 60Hz (United states transmission frequency) hum into the signal.

 

If you want the equipment to be safe and get rid of the hum, you need to at the very least use a quality isolation transformer between the equipment or switch to balanced connects. I have made a loop breaker with a 35 amp bridge rectifier, a resistor, and a cap, this is very safe to do but might not be legal.

[westom]

So are you saying a hum or a buzz is only caused by a particular piece of equipment having an internal problem?

Maybe. Hum also may be created by some inconsistency between two components. Does not matter. Problems are best solved by breaking them down into parts. Then solve each separately - one at a time.

In this case, it does not yet matter what is causing the hum. First determine a circuit that must exist to have that ground loop and hum. An electrical loop must exist. A cheater plug may break the loop in one part; but does not solve the problem A cheater plug can locate one wire in that loop. Doing same for other connected between components defines other parts of that loop.

Once a ground loop is known, then move on to find the defective part. Having defined the loop, one has now enabled the fewer who really know this stuff.

Two types of answers exist. Naive will say "it could be this" or "maybe try that ...". Also called speculation The informed need facts to provide assistance. Facts then enables the informed to make recommendations or even help to define the rest of that loop. What typically results is an answer to fix the problem - not cure symptoms.

xxJPMxx said, "It is not uncommon to have an induced voltage of perhaps 1V RMS between the earth connections of power outlets that are wired separately back to the electrical panel." He has simply defined another connection in the loop. To 'keep it simple', all components should connect to a common receptacle. It is an example of learning that ground loop. If components are connected to separate receptacles and create a hum. And if no hum when all components are powered from the same receptacle, THEN we have defined one part of a ground loop. It might be that safety ground wire between two receptacles. It might be something else. But that fact then empowers the fewer who really know this stuff.

[xxJPMxx]

Once a ground loop is known, then move on to find the defective part.

 

It is most likely the power transformer and not a defective part. This is a very common problem, if you don't want to break the loop at the safety ground it must be broken at the interconnect which requires a quality transformer. http://www.jensen-transformers.com/product/ci-2rr/

Edited November 8, 2015 by xxJPMxx

[babadono]

 

 

http://www.lowes.com/pd_145257-33536-C629171___?productId=1135905&pl=1&Ntt=circuit+breaker+power+cord

 

I had a similar issue with a power amp and adding  a cheater plug also stopped the hum. Through some reading I bought the above power cord that I plugged the cheater plug into for some added safety.   For those in the know does this not make the ungrounded amp safe from possible shocks.g

Nope.

 

Lol, your answer was a bit terse.  Care to elaborate.  If there is a short of some kind in the amp that could cause a shock, would that not trip the circuit breaker in the power cord and cut the power. 

 

Sorry about the short answer, I did not think you wanted an explanation. But briefly, if you have defeated the safety ground anywhere in the cord supplying power to a piece of equipment that has the third prong it does not matter how close to the equipment a circuit breaker is. It will still not trip. If you have a 'fault' in your equipment and the chassis gets energized and the path to ground is open(by installing the cheater) there will be no overload current flow for the breaker to sense.

[mark1101]

As long as you have 1 component in the chain grounded via the 3rd prong, the rest can have ground lifted with a cheater plug.  They are all tied together with RCAs grounding the chassis.  Additionally, if you are lifting ground, your components should be plugged into a GFI outlet which will protect a person from becoming the ground conductor.

 

Another good way to help prevent a ground loop is to plug all components into a single outlet..........not a single circuit, a single outlet.  Use multiple daisy chained power strips if you have to.

[xxJPMxx]

As long as you have 1 component in the chain grounded via the 3rd prong, the rest can have ground lifted with a cheater plug. They are all tied together with RCAs grounding the chassis.

 

True but the sheilding of the RCA cables will most likely melt @ 20A of current.

 

 

 

Another good way to help prevent a ground loop is to plug all components into a single outlet..........not a single circuit, a single outlet.

 

This does indeed help, but there is still a loop, only shorter.

Edited November 9, 2015 by xxJPMxx

[mark1101]

 

As long as you have 1 component in the chain grounded via the 3rd prong, the rest can have ground lifted with a cheater plug. They are all tied together with RCAs grounding the chassis.

 

True but the sheilding of the RCA cables will most likely melt @ 20A or current.

 

 

 

If you are plugged into a GFI, that won't happen.  Shutdown would be instant.  Mine hasn't triggered yet.

[mark1101]

The RCA ground path in addition to the power cord ground path is one source of a loop.

[xxJPMxx]

Sorry I should have clarified. I meant under fault conditions it's not safe to rely on the shielding of the interconnects as the safety ground.

[mark1101]

Right.  I agree.  The ground path for my audio components is one 3 prong plug and RCAs.  Only 1 ground and everything plugged into 1 outlet.  I have probably 12-15 cheater plugs in my system.  Haven't counted in a while.  But I have no hum, only tiny hiss, and a LOT of components.

 

I have over 3800 WPC, a total of 7 amplifiers, 2 preamps, and several source components including Dish network which will give you some hum, and a PC music server.

 

The GFI is what I rely on in case I touch something hot.

 

When our house was built the entire house with the exception of the livingroom and dining room were put on GFI outlets.  Even the master bedroom.

 

So that was already available.

 

If I ever get a shock I'll let everyone know because this is actually a pretty dangerous subject and especially with many of us using vintage equipment that has either been or not been rebuilt.  You never know.

[xxJPMxx]

GFI's are good!   I only have them in certain rooms, like the bathrooms and outdoors. I am only concerned in regard to safety if kids are around, anything else is just culling the herd   I mean really electrical receptacles themselves aren't really safe, kids are always trying to shove stuff in them.

[westom]

 

Another good way to help prevent a ground loop is to plug all components into a single outlet..........not a single circuit, a single outlet.

 

This does indeed help, but there is still a loop, only shorter.

 

 

A shorter loop may not include a voltage difference between two receptacle ground prongs.  Wire is always an electronic component.  A safety ground between two receptacles need not be at the same voltage; might contribute to hum.

 

But again, using a common ground is not a repair. It is a process of identifying the entire offending ground loop.  Fixing the problem comes later.

 

If noise is introduced by a voltage difference between two receptacle safety grounds, then a problem has been identified. Fix what may also be a potential human safety problem in household wiring. Using a cheater plug to mask what must not exist is a classic example of curing symptoms.  In this case to ignore a potentially dangerous defect.  Hum was only a symptom of that defect.

Edited November 9, 2015 by westom

[babadono]

 

Once a ground loop is known, then move on to find the defective part.

 

It is most likely the power transformer and not a defective part. This is a very common problem, if you don't want to break the loop at the safety ground it must be broken at the interconnect which requires a quality transformer. http://www.jensen-transformers.com/product/ci-2rr/

 

Interesting you mention Jensen Transformers. There are resources on their website that will teach you how to locate and fix your ground loop problems. And they use real science not smoke and mirrors. And the real cool thing is they only want to sell you a transformer if you absolutely cannot fix your problem any other safe way.

 

No affiliation with Jensen Transformers yada...yada...yada