Lifting the ground an a Marshall amp

[hrn]

Just wonder if it's harmfull for a 100W Marshall amp to lift the ground on the voltage plug. I'm in Europe, 220 Volts.

Hans

[superspit]

Originally Posted by hrn

Just wonder if it's harmfull for a 100W Marshall amp to lift the ground on the voltage plug. I'm in Europe, 220 Volts.

Hans

Hi HRN,
harmful for the amp or for you? (hate it to be you!!)
I'm sure you can 'ground lift' safer externally, rather than on the amp itself?
I'm sure someone will help you out more betterererer.

[Thurgood]

Let me posite this question? What do you think could become the new path to ground? At 220v. I hope it is not you. Also why are you lifting? Humm? Maybe? I am not an electrician so here is the disclaimer, I am not an electrician or amp tech. However, removing the path to ground is generally not a good idea. I hope someone else will chime in on this as I know some workarounds and ways to solve this type of problem but I am not sticking my neck out to tell you to do it. Better safe than sorry. Not trying to be a jerk by not sharing, I just can't handle the ethical and legal implications.

[hrn]

Thanks guys,
Yes, it's a terrible hum/noise problem. Just trying to find an easy way around it. If I use guitar cables with earth connected at only one side (signal end) would it be so very dangerous then? It's very common with wall plugs here without any earth on them.

Would it be harmful for a Marshall amp do you think? I do it very often with a solid state bass amp getting it dead silent from hum and noise.

Hans

[dementedchord]

never lift a ground on an amp.... back when i was a tech one particular manufacturer would void warranties for this and my boss wouldn't let it outta the shop without one because of liability issues... and at 220/240 it's even more hazardous than our mere 120...

[hrn]

...and if I wear rubber gloves while playing...

[Zaphod B]

Originally Posted by hrn

...and if I wear rubber gloves while playing...

Is there a "latex fetish" forum around here?

[ggunn]

Originally Posted by hrn

Thanks guys,
Yes, it's a terrible hum/noise problem. Just trying to find an easy way around it. If I use guitar cables with earth connected at only one side (signal end) would it be so very dangerous then? It's very common with wall plugs here without any earth on them.

Would it be harmful for a Marshall amp do you think? I do it very often with a solid state bass amp getting it dead silent from hum and noise.

Hans

In the first place, you can't push a signal through a guitar cable that has the shield only connected on one end; the shield is part of the signal path. In the second place, unless you have something else that is connected to ground that is also connected to your amp, then it's not a ground loop that is causing the hum/buzz, and ground lifting the amp will a) do nothing for it, and b) be potentially very dangerous.

[Light]

Originally Posted by hrn

Just wonder if it's harmfull for a 100W Marshall amp to lift the ground on the voltage plug. I'm in Europe, 220 Volts.

Hans

As others have already said, don't do it if you value your life.

For what it is worth, that ground is NOT the cause of your problem. You would be much better served by tracing down the actual source of the hum.


Light

"Cowards can never be moral."
M.K. Gandhi

[MCI2424]

Originally Posted by hrn

Just wonder if it's harmfull for a 100W Marshall amp to lift the ground on the voltage plug. I'm in Europe, 220 Volts.

Hans

Ahh.......................No (if you wanna die).

Don't lift the ground plug especially on 220VAC

Not even at 110VAC

Just don't do it.

[hrn]

Thanks all of you,
I will track the hum without lifting the ground.
Hans

[Greg_L]

It's not the voltage that kills you, its the amperage. Voltage just hurts more.

[Adam P]

Here's a question along similar lines...

I have an old silverface Bassman (70s era, AB165 I believe). I bought it second hand, and the original power cord had been replaced with a three-prong plug, with the ground wire soldered to the amp chassis. The amp has a switch on the back marked "Ground", which I would presume is a ground lift, but it has no other indications. When the switch is flipped to one direction, it works fine. When it is switched the other way, it immediately pops the circuit breaker.

What's going on here? Does it sound like something is shorted? Is this simply caused by the amp being chassis grounded?

Here's a picture for those who aren't familiar (this isn't of my amp, just a picture I found on the Internet):

[superspit]

Originally Posted by Adam P

Here's a question along similar lines...

I have an old silverface Bassman (70s era, AB165 I believe). I bought it second hand, and the original power cord had been replaced with a three-prong plug, with the ground wire soldered to the amp chassis. The amp has a switch on the back marked "Ground", which I would presume is a ground lift, but it has no other indications. When the switch is flipped to one direction, it works fine. When it is switched the other way, it immediately pops the circuit breaker.

What's going on here? Does it sound like something is shorted? Is this simply caused by the amp being chassis grounded?

Here's a picture for those who aren't familiar (this isn't of my amp, just a picture I found on the Internet):

Hi,
I'm going to go out on a limb here..... and say that when you hit the 'ground switch' a 'residual current device' (maybe that is part of your circuit breaker?) trips, indicating that all 3 wires in the AC were being utilised at that time....ie...circuit breaker has found a fault and is tripping to save a life.
Now, if the switch is in the opposite position to the above, only 2 wires (just active and neutral, no earth) are being utilised, therefore RCD/circuit breaker won't trip, because it can't 'see' a fault.
Either way, I would have this amp checked out, or at least metered by a 'competent' person.
I am basing this on the assumption that it is your home's circuit breaker that is tripping, and that it has an RCD as part of it's breaker circuit????
Anyway....just going on what I see here...
Kindest Regards,
Superspit.

[Light]

Originally Posted by Adam P

Here's a question along similar lines...

I have an old silverface Bassman (70s era, AB165 I believe). I bought it second hand, and the original power cord had been replaced with a three-prong plug, with the ground wire soldered to the amp chassis. The amp has a switch on the back marked "Ground", which I would presume is a ground lift, but it has no other indications.

It's not a ground lift, it's a (not) clever little thing which also goes by the colorful name of "the death switch." If I were you, I'd take it to a good amp tech and have them disable it for you, because they really are a bad idea. Basically, what they do is to switch a cap-to-ground between the hot and neutral legs of the incoming Mains. The big problem with them is that, when the cap shorts (as they eventually do), if it is switched to the "hot" side it will send 120v at basically an infinite current to the chassis until it trips the breaker. If you don't have the amp grounded, or if you (through your guitar cable) are a better path to ground, then you may as well have stuck a key in the wall socket, because that is what is going through YOU.

Bad Juju, all around.

By the by, if it is blowing your breaker, it almost certainly means that cap IS blown. That being the case, I need to revise my advice; RUN to the nearest qualified tube amp tech and have them yank that fucker out of there before you turn the amp on again. It may be the cap is just leaky, and your not in danger of getting the full Don King hair treatment, but better safe than sorry, you know?

Seriously, those things EARNED the name "death switch."


Light

"Cowards can never be moral."
M.K. Gandhi

[MCI2424]

Originally Posted by Greg_L

It's not the voltage that kills you, its the amperage. Voltage just hurts more.

Current can't exist without voltage. No voltage, no current.

[Greg_L]

Originally Posted by MCI2424

Current can't exist without voltage. No voltage, no current.

I agree, but high-voltage can be low current. Ever get zapped by a faulty spark-plug wire on a car? Thats several thousand volts, but very low amperage, so it hurts like a motherfucker but won't kill you.

[ggunn]

Originally Posted by Greg_L

I agree, but high-voltage can be low current. Ever get zapped by a faulty spark-plug wire on a car? Thats several thousand volts, but very low amperage, so it hurts like a motherfucker but won't kill you.

Ever get zapped by a spark plug wire while leaning with your crotchal area in contact with the body of the car?

[c7sus]

Originally Posted by MCI2424

Current can't exist without voltage. No voltage, no current.

As little as 18 milliamps can be fatal under the right conditions.

That's 18/1000's of a SINGLE AMP.

And the higher the voltage delivering the current the more likely it can overcome the resistence of your skin.

[Greg_L]

Originally Posted by ggunn

Ever get zapped by a spark plug wire while leaning with your crotchal area in contact with the body of the car?

Yup. It sucked, but still didn't kill me.

[ggunn]

Originally Posted by Greg_L

Yup. It sucked, but still didn't kill me.

Well, of course not. Otherwise, anyone who could have answered "yes" to the question couldn't have answered at all, right? I was just looking for others who share that experience, which is kinda like getting hit simultaneously in the hand and in the nuts with ball peen hammers. I feel your pain.

[dementedchord]

i can kill ya with 12V but i can torure ya with 1200... ummhh boy that can hurt... i got thrown across the room once when i grabbed a 600V line in an old hammond.... it was outta the cabinett and as a smoothing filter they used a separate coil in the speaker (which also provided the magnetism... the speaker was not a permanant mag.. way wierd...) anyhow i had to "jumper" it and it bit me....

[ggunn]

Originally Posted by dementedchord

i can kill ya with 12V but i can torure ya with 1200... ummhh boy that can hurt... i got thrown across the room once when i grabbed a 600V line in an old hammond.... it was outta the cabinett and as a smoothing filter they used a separate coil in the speaker (which also provided the magnetism... the speaker was not a permanant mag.. way wierd...) anyhow i had to "jumper" it and it bit me....

Field coil speaker. Most jukeboxes have them, or used to. They are very efficient, but need high voltage power supplies to run them. I knew an old guy back home who built bass guitar baffles with field coil speakers many years ago.

[Adam P]

Originally Posted by Light

It's not a ground lift, it's a (not) clever little thing which also goes by the colorful name of "the death switch." If I were you, I'd take it to a good amp tech and have them disable it for you, because they really are a bad idea. Basically, what they do is to switch a cap-to-ground between the hot and neutral legs of the incoming Mains. The big problem with them is that, when the cap shorts (as they eventually do), if it is switched to the "hot" side it will send 120v at basically an infinite current to the chassis until it trips the breaker. If you don't have the amp grounded, or if you (through your guitar cable) are a better path to ground, then you may as well have stuck a key in the wall socket, because that is what is going through YOU.

Bad Juju, all around.

By the by, if it is blowing your breaker, it almost certainly means that cap IS blown. That being the case, I need to revise my advice; RUN to the nearest qualified tube amp tech and have them yank that fucker out of there before you turn the amp on again. It may be the cap is just leaky, and your not in danger of getting the full Don King hair treatment, but better safe than sorry, you know?

Seriously, those things EARNED the name "death switch."


Light

"Cowards can never be moral."
M.K. Gandhi

Many thanks. I'll get right on that.

[MCI2424]

Originally Posted by c7sus

As little as 18 milliamps can be fatal under the right conditions.

That's 18/1000's of a SINGLE AMP.

And the higher the voltage delivering the current the more likely it can overcome the resistence of your skin.

What matters is the path the current takes. Many, many more people get shocked through some part of their body, but a fatal shock is directly through the heart. That is what does you in. Never grab anything electrical with both hands. #1 rule in electrical/electronics. TV guys always have 1 hand in their pocket when working on CRT parts.