Ground Lift/Phase switch?

[Colossal]

I'm working on a layout for a Dumble build. I know the Ground Lift switch is generally omitted as we do not want ungrounded amps (!) but I am interested in it from something I read in a story on Joe Bonamassa. For those that follow Joe and his tone, he uses 4 amps (a Van Weelden, a Two Rock or Carol Ann, a Category 5 JB-100 Superlead style custom, and a Marshall Jubilee). The Jubilee is the always-on amp and is combined with any of the other three amps via an A/B/C switch.

I noted on the Joe's Category 5 JB-100 Superlead that S2 included a Phase Switch (see enclosed photo) and I am wondering if this is of similar function or the same thing as a ground lift switch.

Per Joe, <b>"...you've got to get your phasing correct. You have to make sure the ground is proper. If you plugged in my four heads with a normal 3-pronged cable, it would buzz like crazy. You have to go through the rig with ground lifters and painstakingly figure out what to lift and what not to lift to get it as quiet as possible".</b>

Any thoughts or help on the utility of adding this switch would be appreciated. I am planning to run a multi-amp setup in stereo so presume ground loops could be an issue when powering all from a single mains power supply.

Thanks, in advance.

[ayan]

I'm working on a layout for a Dumble build. I know the Ground Lift switch is generally omitted as we do not want ungrounded amps (!) but I am interested in it from something I read in a story on Joe Bonamassa. For those that follow Joe and his tone, he uses 4 amps (a Van Weelden, a Two Rock or Carol Ann, a Category 5 JB-100 Superlead style custom, and a Marshall Jubilee). The Jubilee is the always-on amp and is combined with any of the other three amps via an A/B/C switch.

I noted on the Joe's Category 5 JB-100 Superlead that S2 included a Phase Switch (see enclosed photo) and I am wondering if this is of similar function or the same thing as a ground lift switch.

Per Joe, <b>"...you've got to get your phasing correct. You have to make sure the ground is proper. If you plugged in my four heads with a normal 3-pronged cable, it would buzz like crazy. You have to go through the rig with ground lifters and painstakingly figure out what to lift and what not to lift to get it as quiet as possible".</b>

Any thoughts or help on the utility of adding this switch would be appreciated. I am planning to run a multi-amp setup in stereo so presume ground loops could be an issue when powering all from a single mains power supply.

Thanks, in advance.

This is my 2 cents. Perhapas Joes is talking about speaker phasing when using several amps, in that some could have an even number of common cathode stages and some an odd one, such that at the end they would be out of phase with one another. You could have a phase switch at the speaker jack to flip that and correct the phase. Maybe I'm all off here and Joe is using the term "phase" to discuss something else.

With regards to defeating the chassis ground, this is always a concern because you could end up frying yourself if you did. However, you wouldn't lift the ground on every single amp you used. I believe that if you have the chassis of the amp in which you plug your guitar grounded, then you'd be safe from lethal shocks. However, you could still get shocked... and let me share with you a recent story. To minimize ground loops in my rig, I would keep my amp grounded but would lift the Dumbleator ground to keep things quieter. One day, at a gig, I am setting up and when -- on a dark stage -- I plugged the cords from the Dumbleator to and from my amp, I saw some "light" -- yep, teeny tiny sparks. I frowned and when I touched the guitar strings, they felt "funny," menaning that the ground had obviously been compromised. Why was that? Well, stupid me, I had a "death cap" in my gigging Dumbleator switch and, as you'd have it, it was on other than the MANDATORY neutral position -- my subsequent Dumbleators omitted the ground switch. Needless to say, I unplugged the rig, put the ground switch in the neutral position and grounded the Dumbleator. Evrything was fine after that.

Quite frankly, I would have thought that the fact that the amp was properly grounded would have been good insurance that nothing like that would ever happen, but I was wrong. So, just be careful when lifting the grounds of your rig's components.

Gil

[hairyandy]

I almost always run multi-amp setups, whether it's my own or when I'm working on the SC gig. I now ALWAYS have a Radial Hotshot ABY box around in case of any ground loops or other weird buzzes or hums. The 'B' output of this particular Radial box has a transformer and switches to lift ground and flip phase 180. With the 65 London amps that have an uneven amount of gain stages between the two channels, this box makes it easy to flip phase and use both channels together if you need to. I can't count how many times the ability to transformer isolate a signal has saved my ass!

Andy

[Structo]

Makes sense Gil.

I found a different picture of the JB-100 and it sure looks like they are doing something with the power wiring with that phase switch.

[Colossal]

This is my 2 cents. Perhaps Joes is talking about speaker phasing when using several amps, in that some could have an even number of common cathode stages and some an odd one, such that at the end they would be out of phase with one another. You could have a phase switch at the speaker jack to flip that and correct the phase. Maybe I'm all off here and Joe is using the term "phase" to discuss something else.

Gil,

First, thanks a lot for your response. I too am a bit confused as to exactly what Joe means but it almost seems like he is talking about both speaker phasing <i>and</i> ground lifting, at least that's the way I interpreted it. I'm trying to sort out exactly what the "phase" switch is in his Cat 5 JB-100 Superlead amp does. I did not see one on the Carol Ann or Van Weelden (Dumble Style) amps, but that doesn't mean they aren't there somewhere as Joe had signature models made of those amps as well.

With regards to defeating the chassis ground, this is always a concern because you could end up frying yourself if you did. However, you wouldn't lift the ground on every single amp you used. I believe that if you have the chassis of the amp in which you plug your guitar grounded, then you'd be safe from lethal shocks.

I'm thinking that the master amp (in Joe's case the Jubilee), the guitar would be grounded as its chassis ground would not be lifted but any of the other 3 could be depending on the where any ground loop hum might be lurking. But you are very right that ungrounding an amp is a recipe for potential disaster.

I've enclosed another shot of the JB-100 Superlead amp with this "phase" switch. Looking at it I wonder if it switches polarity but does not defeat the ground (?). Without making a mountain out of this, I am just trying to a) build the quietest multi-amp rig possible with future builds and b) decide whether to include such a switch (in a Dumble style build) if it is of real benefit.

Quite frankly, I would have thought that the fact that the amp was properly grounded would have been good insurance that nothing like that would ever happen, but I was wrong. So, just be careful when lifting the grounds of your rig's components.

Sound advice! Words to [keep] living by.

Thanks.

[txbluesboy]

I think what is happening here is that they are swapping the line and neutral power inputs to prevent a ground loop.

[Colossal]

I think what is happening here is that they are swapping the line and neutral power inputs to prevent a ground loop.

Thanks man, I think you are correct.

[heisthl]

The green wire and the white wire are the same.
Open the fuse box on your house, remove the cover around the breakers, you will see that the hot wires are black and go to their respective breakers, the neutral is white and goes to a common terminal strip and the 3rd wire is bare (ground) and goes to a rod in the dirt, most importamt is that the earth ground and the neutral(white wires) are tied together! So unless your playing in a place that was wired before the codes of the mid 60's, wired by some "handyman" who had no clue or unless you are using a 2 wire extension cord plugged in backwards there is absolutely no need for a ground switch.

[talbany]

Several years ago I hooked up with Joe here in DC @ Blues Alley.. At the time he was intrestred in one of our early Derringers and liked the Idea of the 4X6V amp..He talked at some length about how some amps didn't sound very good with his Marshall and explaind it had to do with speaker phasing when running 2 amps.. I remember asking him if he was refuering to AC phasing he said no speaker phasing...he was pretty passionate about it..It's has been a while but I am pretty sure that's what he said..

.

..you've got to get your phasing correct. You have to make sure the ground is proper. If you plugged in my four heads with a normal 3-pronged cable, it would buzz like crazy. You have to go through the rig with ground lifters and painstakingly figure out what to lift and what not to lift to get it as quiet as possible".

This to me sure sounds like AC phasing and grounding issues..





Tony VVT

[Tavda3172]

Hi Guys,
I have worked with a lot of pro studio gear and a ground lift switch should lift the circuit ground (this connection should remain grounded at RF). The safety ground should NEVER be lifted or disconnected. In order to do this you have to lay out your grounding very carefully and only have one connection from the circuit to the chassis, which is tricky if you are used to building things with random grounds. This will allow you to eliminate ground loops if/when they happen and keep you safe from electrical shock. I'm not sure how Joe's gear is built or laid out but I can only hope that they aren't eliminating the safety ground.
-Kevin

[txbluesboy]

Never mind-stupid post.

[M Fowler]

Dave,

That looks like to me a polarity switch as used in many old Fenders since it is using only the black and white wires (ground and neutral) and the switch has the X pattern wiring to the terminals, to switch polarity between the two paths.

Mark

[Colossal]

I have decided to retract my opinion that they are swapping the line and neutral wires as that could cause some real problems. It might be that they are lifting the neutral wire (assuming this is a 115 volt amp ) and using the ground prong as the neutral return. I only see two wires going to the switch. I've never seen this done and don't think it would be up to code but it would work and might prevent a ground loop.

The amp in question does have a mains voltage select switch (120/220V). I spent the morning studying the pictures and drew up a schematic as best I could. It was tricky following the various wires through that twisted bundle over the PT, but I am pretty darn certain it is flipping the black load wire (coming from the fuse) and the white neutral wire from the mains.

Dave,

That looks like to me a polarity switch as used in many old Fenders since it is using only the black and white wires (ground and neutral) and the switch has the X pattern wiring to the terminals, to switch polarity between the two paths.

Mark

Mark,

I'm pretty sure now that's what it is. You're right, you can clearly see the X pattern on the switch.

[heisthl]

It would seem to me that JB needs an amp tech who can correct some of the amps in his set up so every amp is the same and can all plug into the same source using the 3 prong cords without issues.

[M Fowler]

There was a youtube video with JB talking about his grounding of his amps in his rig? Or I better thumb through my collection of guitar mags as I know he recent talked about ground loops. I'll check but my place is a mess still.

Mark