"Floating Ground" - What do they mean?

Guest
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.

If the DC voltmeter is AC powered, Float the AC ground wire.

I (sort of) understand what they mean by a "Floating Ground", but I'm
not exactly sure what they mean. And, if I was to use a VTVM which is
plugged into the AC line, or an Oscilloscope (also plugged into an
outlet), how do I achieve a "floating ground"?

Now, lets say I use a pocket battery operated VOM. It's not plugged in,
so there is no ground. Is that safe to use on this device? (Seems to me
that a pocket VOM is NOT actually grounded to earth, so that WOULD be a
floating ground. (I think)....
 
The Old Fart wrote:
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.

If the DC voltmeter is AC powered, Float the AC ground wire.

I (sort of) understand what they mean by a "Floating Ground", but I'm
not exactly sure what they mean. And, if I was to use a VTVM which is
plugged into the AC line, or an Oscilloscope (also plugged into an
outlet), how do I achieve a "floating ground"?
Click to expand...

** You can't do it with good safety.

Disconnecting the AC ground does it unsafely.


Now, lets say I use a pocket battery operated VOM. It's not plugged in,
so there is no ground. Is that safe to use on this device? (Seems to me
that a pocket VOM is NOT actually grounded to earth, so that WOULD be a
floating ground. (I think)....
Click to expand...

** Of course.

The amp uses bridge mode output - right ?

So both speaker terminals are amp outputs.

So all YOU do is measure one of them to ground with your VTVM or scope and double the reading.


...... Phil
 
olds...@tubes.com:

Floating ground = shared, at least in my
experience.

On my early '80s GM stock stereo, there
were speaker outputs for four speakers
as follows:

Left-Front Positive, Left-Rear Positive,
and a single Left-Minus(both left speakers
Minus wires tied into that). Ditto on the
Right. It was called 'floating' ground
because there weren't individual negative
leads for the front and rear speakers
on each side.

Probably done to save space and money
by using less copper.
 
On 22/04/17 06:35, oldschool@tubes.com wrote:
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.

If the DC voltmeter is AC powered, Float the AC ground wire.

I (sort of) understand what they mean by a "Floating Ground", but I'm
not exactly sure what they mean. And, if I was to use a VTVM which is
plugged into the AC line, or an Oscilloscope (also plugged into an
outlet), how do I achieve a "floating ground"?
Click to expand...

Use a safety isolation transformer, or batteries.

--
Adrian C
 
Adrian Caspersz wrote:



Use a safety isolation transformer, or batteries.
Click to expand...

** FFS - that IS absurd advice from another fucking, know nothing "phrase matching" idiot.



..... Phil
 
On Friday, April 21, 2017 at 11:37:24 PM UTC-7, olds...@tubes.com wrote:
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.
Click to expand...

Possibly it means that the 'ground' terminals are actually connected to the
AC neutral wire (not to a third-wire ground). That connection is
permitted only with limiting resistance so that shock hazard is nil,
but 'test equipment' can easily see high-voltage transients.

That would make sense only if this is a two-wire AC powered gizmo.
It would make MORE sense if the device were an old TV set.
 
whit3rd wrote:

Possibly it means that the 'ground' terminals are actually connected to the
AC neutral wire (not to a third-wire ground). That connection is
permitted only with limiting resistance so that shock hazard is nil,
but 'test equipment' can easily see high-voltage transients.

That would make sense only if this is a two-wire AC powered gizmo.
It would make MORE sense if the device were an old TV set.
Click to expand...

** You know something, just because you see a question posted on this NG - that does not mean you have to try an answer it.

FFS - it was not posted to you.

If you haven't got a clue - shut the fuck up.



..... Phil
 
On 22/04/17 11:23, Phil Allison wrote:
Adrian Caspersz wrote:

Use a safety isolation transformer, or batteries.


** FFS - that IS absurd advice from another fucking, know nothing "phrase matching" idiot.
Click to expand...

Use of a mains isolation transformer allows a safe floating ground
reference. I've done that with 'scopes on a live television chassis,
with a 500W lump of a 240V/240V transformer.

Nice day outside?

--
Absurd C
 
On 4/22/2017 1:54 AM, Phil Allison wrote:
The amp uses bridge mode output - right ?

So both speaker terminals are amp outputs.
Click to expand...

I'm going to go with this as the correct answer.
The audio output of a Motorola Spectra is like this, and
there are warnings repeatedly through the service manual
NOT to ground either side of the audio.

This has nothing to do with "hot chassis" or floating
grounds.


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com
 
In article <7cqlfcp3p9t9pu6f192morv3991n86bidl@4ax.com>,
oldschool@tubes.com says...
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.

If the DC voltmeter is AC powered, Float the AC ground wire.

I (sort of) understand what they mean by a "Floating Ground", but I'm
not exactly sure what they mean. And, if I was to use a VTVM which is
plugged into the AC line, or an Oscilloscope (also plugged into an
outlet), how do I achieve a "floating ground"?

Now, lets say I use a pocket battery operated VOM. It's not plugged in,
so there is no ground. Is that safe to use on this device? (Seems to me
that a pocket VOM is NOT actually grounded to earth, so that WOULD be a
floating ground. (I think)....
Click to expand...

There are 2 possibilities. The first one that comes to mind is the 'hot
chassis' where one side of the AC line is connected to the chassis.
Usually an isolation transformer is used, or battery powered instruments
that do not have a ground or conductive case.

The other is for mainly transistor audio output amplifiers. The speaker
has both leads floating above ground. If a meter is used that one side
of the test leads go to the chassis and the chassis of the meter is
grounded by the 3 wire AC plug, the amp will be dammaged.

The same for the battery powered meter applies. If it does not have a
conductive chassis and no AC line cord then you can use it.


Another rare,but possiable case is that a 'ground loop' can be made
where a lot of hum or other undesired signals can be made.
 
"Ralph Mowery" wrote in message
news:MPG.3365329ffcfd725e9898dd@news.east.earthlink.net...

In article <7cqlfcp3p9t9pu6f192morv3991n86bidl@4ax.com>,
oldschool@tubes.com says...
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.

If the DC voltmeter is AC powered, Float the AC ground wire.

I (sort of) understand what they mean by a "Floating Ground", but I'm
not exactly sure what they mean. And, if I was to use a VTVM which is
plugged into the AC line, or an Oscilloscope (also plugged into an
outlet), how do I achieve a "floating ground"?

Now, lets say I use a pocket battery operated VOM. It's not plugged in,
so there is no ground. Is that safe to use on this device? (Seems to me
that a pocket VOM is NOT actually grounded to earth, so that WOULD be a
floating ground. (I think)....
Click to expand...

There are 2 possibilities. The first one that comes to mind is the 'hot
chassis' where one side of the AC line is connected to the chassis.
Usually an isolation transformer is used, or battery powered instruments
that do not have a ground or conductive case.

The other is for mainly transistor audio output amplifiers. The speaker
has both leads floating above ground. If a meter is used that one side
of the test leads go to the chassis and the chassis of the meter is
grounded by the 3 wire AC plug, the amp will be dammaged.

The same for the battery powered meter applies. If it does not have a
conductive chassis and no AC line cord then you can use it.


Another rare,but possiable case is that a 'ground loop' can be made
where a lot of hum or other undesired signals can be made.





********************************************************


There is another situation whereby some stereo power amplifiers polarity
swap the inputs and outputs, so that on one channel the negative (black)
speaker terminal is at ground, but the other side has the positive (red)
terminal at ground, and the power amp output connected to black.

It would not be immediately obvious that one channels "black" terminal is
actually the power amp output. Connecting this to ground would short the
amplifier.


This is done to maximise the efficiency of the power supply common to both
channels.



Gareth.
 
How about you post the make and model of the thing so we can see how it is configured and explain better ?
 
On Sat, 22 Apr 2017 08:21:01 -0500, Foxs Mercantile <jdangus@att.net>
wrote:

On 4/22/2017 1:54 AM, Phil Allison wrote:
The amp uses bridge mode output - right ?
So both speaker terminals are amp outputs.

I'm going to go with this as the correct answer.
The audio output of a Motorola Spectra is like this, and
there are warnings repeatedly through the service manual
NOT to ground either side of the audio.

This has nothing to do with "hot chassis" or floating
grounds.
Click to expand...

I just hate to agree with you, but y're right. Nobody builds AC-DC
transformerless radios and audio amps these daze.

It's probably a bridge amp:
<https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers>
That looks like this:
<https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#/media/File:Bridge_amp.GIF>
Notice that neither speaker wire is grounded.

If you want to look at the output of a bridge amp with a scope, you
need to have a scope with an A-B (that's channel A minus channel B)
input. Connect one probe each from each scope channel to each speaker
lead. Connect both scope ground leads to ground.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
Foxs Mercantile wrote:
Phil Allison wrote:

The amp uses bridge mode output - right ?

So both speaker terminals are amp outputs.


I'm going to go with this as the correct answer.
The audio output of a Motorola Spectra is like this, and
there are warnings repeatedly through the service manual
NOT to ground either side of the audio.

This has nothing to do with "hot chassis" or floating
grounds.
Click to expand...

** The OldFart claims the manual says:

"If the DC voltmeter is AC powered, Float the AC ground wire."

That can only refer to a VTVM.

Few techs have used them beyond the 1960s.

His idea of "high powered" could mean anything - maybe some Germanium pile of shit from the early 60s.


...... Phil






Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com
Click to expand...
 
"Gareth Magennis" wrote in message news:A1OKA.537183$4n3.303630@fx14.am4...



"Ralph Mowery" wrote in message
news:MPG.3365329ffcfd725e9898dd@news.east.earthlink.net...

In article <7cqlfcp3p9t9pu6f192morv3991n86bidl@4ax.com>,
oldschool@tubes.com says...
I'm looking at a repair manual for a high powered transistorized audio
amplifier. It repeatedly says:

DO NOT use any test equipment to test or evaluate this amplifier, which
does not have floating grounds.

If the DC voltmeter is AC powered, Float the AC ground wire.

I (sort of) understand what they mean by a "Floating Ground", but I'm
not exactly sure what they mean. And, if I was to use a VTVM which is
plugged into the AC line, or an Oscilloscope (also plugged into an
outlet), how do I achieve a "floating ground"?

Now, lets say I use a pocket battery operated VOM. It's not plugged in,
so there is no ground. Is that safe to use on this device? (Seems to me
that a pocket VOM is NOT actually grounded to earth, so that WOULD be a
floating ground. (I think)....
Click to expand...

There are 2 possibilities. The first one that comes to mind is the 'hot
chassis' where one side of the AC line is connected to the chassis.
Usually an isolation transformer is used, or battery powered instruments
that do not have a ground or conductive case.

The other is for mainly transistor audio output amplifiers. The speaker
has both leads floating above ground. If a meter is used that one side
of the test leads go to the chassis and the chassis of the meter is
grounded by the 3 wire AC plug, the amp will be dammaged.

The same for the battery powered meter applies. If it does not have a
conductive chassis and no AC line cord then you can use it.


Another rare,but possiable case is that a 'ground loop' can be made
where a lot of hum or other undesired signals can be made.





********************************************************


There is another situation whereby some stereo power amplifiers polarity
swap the inputs and outputs, so that on one channel the negative (black)
speaker terminal is at ground, but the other side has the positive (red)
terminal at ground, and the power amp output connected to black.

It would not be immediately obvious that one channels "black" terminal is
actually the power amp output. Connecting this to ground would short the
amplifier.


This is done to maximise the efficiency of the power supply common to both
channels.



Gareth.







************************************************************


To clarify, most amps using this method don't actually have red and black
terminals, but use Speakon connectors, where the terminals are not visible.
One Speakon is wired 1+ hot, 1- ground, the other is wired the opposite,
with the signal input to the amplifier polarity reversed.
The end user doesn't need to know or care this is the case when using
Speakons, but a repair tech certainly does.

One notable user of this method is the Yamaha Stagepass series, which has
1/4 inch jack outputs. In this case, one side has the jack body grounded
and the power amp output going to the tip, whilst the other has the tip
grounded and the jack body is actually live.
A terrible idea really.



Gareth.
 
On Sat, 22 Apr 2017 18:56:51 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sat, 22 Apr 2017 08:21:01 -0500, Foxs Mercantile <jdangus@att.net
wrote:

On 4/22/2017 1:54 AM, Phil Allison wrote:
The amp uses bridge mode output - right ?
So both speaker terminals are amp outputs.

I'm going to go with this as the correct answer.
The audio output of a Motorola Spectra is like this, and
there are warnings repeatedly through the service manual
NOT to ground either side of the audio.

This has nothing to do with "hot chassis" or floating
grounds.

I just hate to agree with you, but y're right. Nobody builds AC-DC
transformerless radios and audio amps these daze.

It's probably a bridge amp:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers
That looks like this:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#/media/File:Bridge_amp.GIF
Notice that neither speaker wire is grounded.

If you want to look at the output of a bridge amp with a scope, you
need to have a scope with an A-B (that's channel A minus channel B)
input. Connect one probe each from each scope channel to each speaker
lead. Connect both scope ground leads to ground.
Click to expand...

You're right. First off, it has a power transformer.
Secondly it is an amp made to be bridged. After reading the user manual
a second time, I determined that this floating ground is only needed in
Bridge mode.

I have never had an amp that was bridgable (that I know of anyhow). I
dont think this is possible with the old tube amps, but I could be
wrong. This amp is a solid state, with power transistors (not chips for
the output). 16 power transistors to be exact.

Although I like tube amps, I could not pass this amp up for the price he
wanted. It's rated at 300W per channel using 4ohm speaker load, or 200W
per channel using 8 ohm speakers. Or it's brigable to be a 600W mono
amp. I'm gonna have fun with this thing....

It's a Altec Lansing 9444A power amp. It appears it was made around 1988
to 1990.
And Altec Lansing is top of the line equipment.

This is a commercial amp, with balanced XLR inputs, so I will have to
buy or make some adaptors so I can connect 1/4" or RCA jacks to it for
home use. But I know that my speakers wont handle that full power
either, but I suppose I dont have to run it wide open either....
 
Some Old Fart olds...@tubes.com wrote:
Phil Allison wrote:
The amp uses bridge mode output - right ?
So both speaker terminals are amp outputs.

I'm going to go with this as the correct answer.
The audio output of a Motorola Spectra is like this, and
there are warnings repeatedly through the service manual
NOT to ground either side of the audio.

This has nothing to do with "hot chassis" or floating
grounds.

I just hate to agree with you, but y're right. Nobody builds AC-DC
transformerless radios and audio amps these daze.

It's probably a bridge amp:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers
That looks like this:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#/media/File:Bridge_amp.GIF
Notice that neither speaker wire is grounded.

If you want to look at the output of a bridge amp with a scope, you
need to have a scope with an A-B (that's channel A minus channel B)
input. Connect one probe each from each scope channel to each speaker
lead. Connect both scope ground leads to ground.


You're right. First off, it has a power transformer.
Secondly it is an amp made to be bridged. After reading the user manual
a second time, I determined that this floating ground is only needed in
Bridge mode.

I have never had an amp that was bridgable (that I know of anyhow). I
dont think this is possible with the old tube amps, but I could be
wrong.
Click to expand...

** You are.



This amp is a solid state, with power transistors (not chips for
the output). 16 power transistors to be exact.

Although I like tube amps, I could not pass this amp up for the price he
wanted. It's rated at 300W per channel using 4ohm speaker load, or 200W
per channel using 8 ohm speakers. Or it's brigable to be a 600W mono
amp. I'm gonna have fun with this thing....

It's a Altec Lansing 9444A power amp. It appears it was made around 1988
to 1990.
And Altec Lansing is top of the line equipment.
Click to expand...

** Altec & Lansing are loudspeaker brands.

That amp is just some "badge engineered" POS.



This is a commercial amp, with balanced XLR inputs, so I will have to
buy or make some adaptors so I can connect 1/4" or RCA jacks to it for
home use. But I know that my speakers wont handle that full power
either, but I suppose I dont have to run it wide open either....
Click to expand...

** Be a devil - let the badger loose ....



..... Phil
 
oldschool@tubes.com wrote:
On Sat, 22 Apr 2017 18:56:51 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

On Sat, 22 Apr 2017 08:21:01 -0500, Foxs Mercantile <jdangus@att.net
wrote:

On 4/22/2017 1:54 AM, Phil Allison wrote:
The amp uses bridge mode output - right ?
So both speaker terminals are amp outputs.

I'm going to go with this as the correct answer.
The audio output of a Motorola Spectra is like this, and
there are warnings repeatedly through the service manual
NOT to ground either side of the audio.

This has nothing to do with "hot chassis" or floating
grounds.

I just hate to agree with you, but y're right. Nobody builds AC-DC
transformerless radios and audio amps these daze.

It's probably a bridge amp:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers
That looks like this:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#/media/File:Bridge_amp.GIF
Notice that neither speaker wire is grounded.

If you want to look at the output of a bridge amp with a scope, you
need to have a scope with an A-B (that's channel A minus channel B)
input. Connect one probe each from each scope channel to each speaker
lead. Connect both scope ground leads to ground.

You're right. First off, it has a power transformer.
Secondly it is an amp made to be bridged. After reading the user manual
a second time, I determined that this floating ground is only needed in
Bridge mode.

I have never had an amp that was bridgable (that I know of anyhow). I
dont think this is possible with the old tube amps, but I could be
wrong. This amp is a solid state, with power transistors (not chips for
the output). 16 power transistors to be exact.

Although I like tube amps, I could not pass this amp up for the price he
wanted. It's rated at 300W per channel using 4ohm speaker load, or 200W
per channel using 8 ohm speakers. Or it's brigable to be a 600W mono
amp. I'm gonna have fun with this thing....

It's a Altec Lansing 9444A power amp. It appears it was made around 1988
to 1990.
And Altec Lansing is top of the line equipment.
Click to expand...

It was popular for industrial and commercial sound systems. It was a
US company, and I've seen their equipment for decades. I've been out of
the business for years, so I don't know if they are still around.

Some stadiums used their equipment, with thousands of watts of
amplification, with each amp driving a single zone. Some had N+1
installations that would automatically switch a spare amp into service
if needed.


This is a commercial amp, with balanced XLR inputs, so I will have to
buy or make some adapters so I can connect 1/4" or RCA jacks to it for
home use. But I know that my speakers wont handle that full power
either, but I suppose I don't have to run it wide open either....
Click to expand...

Here is the manual, which shows how to connect an unbalanced input.

<https://www.manualslib.com/download/365773/Altec-Lansing-9444a-Power-Amplifier.html>


--
Never piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)
 
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