Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
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).... |
#2
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
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"? ** 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).... ** 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 |
#3
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
:
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. |
#4
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
|
#5
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
Adrian Caspersz wrote:
Use a safety isolation transformer, or batteries. ** FFS - that IS absurd advice from another ****ing, know nothing "phrase matching" idiot. ..... Phil |
#6
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
On Friday, April 21, 2017 at 11:37:24 PM UTC-7, 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. 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. |
#7
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
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. ** 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 **** up. ..... Phil |
#8
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
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 ****ing, know nothing "phrase matching" idiot. 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 |
#9
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
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. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com --- This email has been checked for viruses by AVG. http://www.avg.com |
#10
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
|
#11
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
How about you post the make and model of the thing so we can see how it is configured and explain better ?
|
#12
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
On Sat, 22 Apr 2017 08:21:01 -0500, Foxs Mercantile
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. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#13
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
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. ** 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 **** 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 |
#14
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
On Sat, 22 Apr 2017 18:56:51 -0700, Jeff Liebermann
wrote: On Sat, 22 Apr 2017 08:21:01 -0500, Foxs Mercantile 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. 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.... |
#15
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
Some Old Fart 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. ** 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. ** 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.... ** Be a devil - let the badger loose .... ..... Phil |
#16
Posted to sci.electronics.repair
|
|||
|
|||
"Floating Ground" - What do they mean?
|
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
"floating" wall | UK diy | |||
How to connect "signal ground" terminals? (and DC power negative) | Metalworking | |||
"Earth" floating at 80-120V ... why? | UK diy | |||
2 "ground rod" questions (Thumper aka cable fault locator) | Home Repair | |||
Outcome (was 2 "ground rod" questions (Thumper aka cable fault locator)) | Home Repair |