Ground out" Adapter to reduce hum.Dangerous?

DJ Sillito · Post by **DJ Sillito** » 25 Sep 2001 3:37 pm

I have an adapter which converts a three pronged extension cord to a two pronged cord. Basically this is removing the ground portion of the cord. I heard Jeff Newman mention that this can be used to get rid of the hum we sometimes encounter when we plug in on stage depending on how the the stage was wired. Well I tried it and it worked, however,
1. This adapter I found out is not sold in Canada because it may be considered a fire hazzard.

2. Also I was afraid that if your amp was running through a grounded circuit and your mic was plugged into the PA which was not grounded could you run the risk of being zapped so to speak. Essentially you become the ground?

If anyone with some electrical background could help I would appreciate your comments. I know very little in this area. I don't want to risk the safety of the other band members.

Thank you much!

DOC DJ

Blake Hawkins · Post by **Blake Hawkins** » 25 Sep 2001 3:56 pm

DJ,
Your concerns are correct. The ground wire on your amp is a Safety Ground and is ment to protect you if a power transformer shorts out or any other malfunction which would place voltage on the ground.

In stage work with amplifiers it is better to have other solutions to get rid of the ground hum.
If the ground loop is between you and the PA, you could plug into the same circuit which is providing power to the PA.
You could try different outlets on the stage
in an effort to find one which will not hum.
You could obtain an audio isolation transformer and connect that in your signal line.
All of the above assume that you are connecting your amp to the PA or other sound system and the ground loop is caused by a difference in voltage between them.
This trouble happens most often in unbalanced audio systems which are used on musical instruments. It is possible to obtain a balance box which will convert your output to a balanced line and elemiate the hum.
Defeating the safety ground can give you a nasty shock in the USA or Canada...in Europe where the mains are 220 to 240 volts it can be fatal.
Blake

[This message was edited by Blake Hawkins on 25 September 2001 at 04:58 PM.]

CrowBear Schmitt · Post by **CrowBear Schmitt** » 26 Sep 2001 2:48 am

i will agree w: Blake.
i would'nt disconnect the Ground because it's being there, is Vital to Safety.
Blake is also correct about finding other plugs ( or lines) that won't have hum.
it is rare for amps to be plugged into lines having Stage Lighting on them 'cause they sure do cause Hummmmm... (humaditty)
Steel grounded

Glenn Austin · Post by **Glenn Austin** » 26 Sep 2001 6:50 am

There is a great article at www.rane.com about grounding and sound system interconnection. It explains everything.

DJ Sillito · Post by **DJ Sillito** » 27 Sep 2001 9:49 am

Thank you for the comments Glen , Crowbear , And Blake. I'll try the website for more info. The instructional video I have explaining the profex II and the session 2000 etc. had Jeff Newman mentioning the use of the adapter and even resorting to cutting the ground off with a pair of pliers. However I'll have to watch it again to get the full context of what he mentioned. He may have been explaining a hum problem between his amp and the Preamp (DP 750, I think). Anyways I think he knows what he's doing. The problem is I don't know when it comes to electrical questions. I just didn't want anyone else to get hurt if they use this adapter for the wrong situation.

Thanks again,

DJ

Jack Stoner · Post by **Jack Stoner** » 27 Sep 2001 11:20 am

Removing the "protective" ground is not the thing to do. I've never watched the Newman tape but you have to have at least one unit grounded for safety. If you run two separate amps (e.g. two Nashville 400's) and a preamp/processor, such as a Profex II there is a possiblity of a difference in ground potential or hum or "ground loop hum". However, one of the amps must remain grounded and then everything is basically grounded through the one amp. This is not the best way but an option.

With one amp and a Profex II , you should not have any ground loop hum. If you do you have major problems.

If the Newman tape tells you to cut off all the ground lugs that is "dead" wrong.

Bobby Boggs · Post by **Bobby Boggs** » 27 Sep 2001 9:12 pm

I'd never thought about this as a personal hazard.None of my Fender amps have the 3 prong plugs.And a couple of them are nearly 40 years old.Original cords too.Do I like to live dangerously or what?

-------bb[This message was edited by Bobby Boggs on 27 September 2001 at 10:45 PM.]

George Rozak · Post by **George Rozak** » 27 Sep 2001 9:31 pm

I've got an old Fender Princeton Reverb with a 2 prong plug also. I've been considering changing it to a 3 prong. Any suggestions or comments as to the best way to do this?

Rich Paton · Post by **Rich Paton** » 28 Sep 2001 1:54 am

George, try posting your question here, for good answers. It's all good folks there as well... http://www.firebottle.com/fireforum/fireBB.cgi
I've been an industrial electrician / part-time musician almost 30 years now...I always check all the receptacles a band will be using at a venue for proper configuration, and have seen too many electrical "case studies" & horror stories in clubs. One bowling-alley dive we worked regularly had a series of beat to hell plugmold strips lying along the back of the stage, strung together & connected to the source of power with a disgusting looking hank of old Romex cable with a plug attached to it. Probably 12 or so receptacles in it, and every one tested differently! Reverse polarity, open grounds, intermittents and everything between. I christened it "The Death Strip" and never used it fr my gear.
You have to be really careful out there in the "real world" of electrical hazards.
Found one duplex receptacle in the stage area of a club, which some cretain had ponied into a 277 VAC lighting circuit.
Please be careful...always check all receptacles for proper connections & voltage before you connect anything to it! If it don't do YOU in, it could easily do your Quadraverb, Profex, & power amp in, quicker than you can say "zzzzzzzzzzzzffffffft!

Blake Hawkins · Post by **Blake Hawkins** » 28 Sep 2001 5:47 am

I've seen similar electrical horrors as described by Rich.
I carry one of those "Test" plugs with the three lights which shows you if the plug is wired correctly. They are inexpensive and are available at Home Depot, Lowes, and similar stores.
Although I have seen it many times, you should NEVER cut the ground pin off your amp plug. If you MUST operate from an older two wire circuit, then take along one of the "Ground Lift" adapters to use in that instance. (or you could refuse to set up until the venue operator gave you proper and safe power.)
I, too, have an old Fender Deluxe (5B3)Amp which I use. Many years ago, I installed a 3 wire cord and eliminated the "Line Bypass"
capacitor.
There was a thread on this modification some time ago on the forum and some one had a link to a site which had detailed instructions on replacing the line cord.
It's not something to do yourself unless you
are a qualified tech.
The old amps with the two prong plugs and the ground switch were made in a time before the safety ground was required in electrical wiring. The Neutral side of the line (white wire) is grounded. The amps had a bypass cap from one side of the line to chassis ground. Trouble was, since the two prong plug would go in either way, you couldn't tell which side of the line went to the chassis through the cap. If you got a hum or a mild shock, you would turn the plug over and things would be OK. The Fender amps had the cap on a switch which would put the cap on either side of the line so you didn't have to umplug the amp to get rid of the hum/shock. Over time the caps developed
current leakage or, in some cases just shorted out. Then you got the full line voltage and a nasty shock.
Later, the two wire sockets had one wide and one narrow pin...the wide pin was the neutral, but they could still be wired incorrectly.
Blake
[This message was edited by Blake Hawkins on 28 September 2001 at 03:16 PM.]

Johan Jansen · Post by **Johan Jansen** » 1 Oct 2001 10:21 am

When I hear a ground-hum, some little voice inside my head says it's not safe!
A good circuit does not hum, period!
Never play with your life!
JJ

DJ Sillito · Post by **DJ Sillito** » 5 Oct 2001 7:39 am

I watched the video with Jeff Newman again and what he said was if you are using two amplifiers with your profex unit to get the stereo effect you may encounter some hum in the system. He said if you use the adapter on ONE of the amplifiers it will reduce or remove the hum. This makes a little more sense nd doesn't seem quite as hazzardous.!?
Anyway thanks to those who answere my question

Rich Paton · Post by **Rich Paton** » 10 Oct 2001 5:36 pm

I haven't delved into the theory behind the use of those amps using double throw switches & capacitors, so I really have no idea how they are supposed to work.
However, the basic premise behind using a grounded cord and connectors (on amps, sound gear, and/or ANY appliance or equipment which comes supplied with a "three prong cord" is to ~attempt~ to ensure this:
In the event that for whatever reason the "hot" side of an AC circuit should make contact with the chassis (and therefore your signal cable connectors, guitar strings, microphones, etc), having the chassis solidly grounded should cause the "fault clearing equipment" of the power distribution system of a facility (circuit breakers, fuses, or lately, possibly more sophisticated fault-detecting circuits) will open (tripped breaker, blown fuse, actuated fault detector(s)) and thereby remove the source of power until such a fault is "cleared" (unplugged and repaired) from the circuit. This action, of course, depends on having a good, solid connection from the equipment back to the breaker panel or fuse panel which powers the circuit.
I can assure you that such optimal connections are often comprimised in the "real world". Even using an extension cord which is rolled up in a coil can (and often does) comprimise the ground return path.
Murphy's law states that %^&* can and will happen, so the best option is always to correct any such fault and not remove the design elements (ground prong etc.) incorporated into equipment to ensure safety against electrical shock.
When in doubt, have your gear and (ALWAYS is my rule on this) the circuits you connect it to checked, to play it safe!
Considering what I've seen in electrical wiring installations, I'm ALWAYS in doubt.