Dick,
It has actually been in the National Electrical code for some time (Ca. 1970!) for a single point of safety ground to neutral connection. Electrical supply houses all sell optional isolated ground bus bars for sub-panels. It has taken practicing electricians some time to note the change! (I don't know when they added the class 2 to the mix though.)
Of course if the safety ground is tied to the neutral at the sub-panels then every safety ground has a different voltage on it. Interconnecting gear on different sub-panels makes the shield carry current and often lots of it!
Now more folks are getting fussy about how the the neutral is handled in the sub-panel to minimize hot leg balancing currents. So of course one noted consultant asks for a neutral for each hot. (For those who don't get it, if I have three sub-woofer amplifiers and three phase power, by using one hot for each amplifier there should be no current on the neutral.)
George,
I forgot to mention the consultants' also specify a separate technical ground. So at the building entrance the neutral and safety ground are tied to an actual earth ground and the incoming neutral. Now in a typical installation the actual ground system will be around 30 ohms. (Really!) The combined neutral/ground will be below 3 ohms, as it is tied into many other ground points. So due to current in the neutral there is always some actual voltage above ground at the neutral/ground tie. This voltage will now have a second path from the safety ground through the chassis to the ground buss and back to earth through the second ground point.
Even using the original neutral/ground connection will result in some current flow as the safety ground wire in it's travels to the sub-panels and outlets will pick up stray currents from inductive coupling, capacitive coupling and of course from the current it has to sink from power line filters and SY's internal transformer shield. So if you run a clean isolated wire to the ground point you will often measure substantial voltage between that and the safety ground. Many folks call this a ground loop thinking the voltage difference is impressed by stray magnetic fields. If you do the math for a loop that big the magnetic field would be large enough to rattle your key chain.
If the voltage between the safety ground and the neutral is less than 6 volts, most modern gear can handle it without adding hum. More than that is a problem.
ES
It has actually been in the National Electrical code for some time (Ca. 1970!) for a single point of safety ground to neutral connection. Electrical supply houses all sell optional isolated ground bus bars for sub-panels. It has taken practicing electricians some time to note the change! (I don't know when they added the class 2 to the mix though.)
Of course if the safety ground is tied to the neutral at the sub-panels then every safety ground has a different voltage on it. Interconnecting gear on different sub-panels makes the shield carry current and often lots of it!
Now more folks are getting fussy about how the the neutral is handled in the sub-panel to minimize hot leg balancing currents. So of course one noted consultant asks for a neutral for each hot. (For those who don't get it, if I have three sub-woofer amplifiers and three phase power, by using one hot for each amplifier there should be no current on the neutral.)
George,
I forgot to mention the consultants' also specify a separate technical ground. So at the building entrance the neutral and safety ground are tied to an actual earth ground and the incoming neutral. Now in a typical installation the actual ground system will be around 30 ohms. (Really!) The combined neutral/ground will be below 3 ohms, as it is tied into many other ground points. So due to current in the neutral there is always some actual voltage above ground at the neutral/ground tie. This voltage will now have a second path from the safety ground through the chassis to the ground buss and back to earth through the second ground point.
Even using the original neutral/ground connection will result in some current flow as the safety ground wire in it's travels to the sub-panels and outlets will pick up stray currents from inductive coupling, capacitive coupling and of course from the current it has to sink from power line filters and SY's internal transformer shield. So if you run a clean isolated wire to the ground point you will often measure substantial voltage between that and the safety ground. Many folks call this a ground loop thinking the voltage difference is impressed by stray magnetic fields. If you do the math for a loop that big the magnetic field would be large enough to rattle your key chain.
If the voltage between the safety ground and the neutral is less than 6 volts, most modern gear can handle it without adding hum. More than that is a problem.
ES
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Figure 1 is without the diodes, Figure 2 is with. There is 10 db less noise from the 120 Hz modulation and 30% duty cycle.
As there are inductances and capacitances in real circuits there is less overall and momentary noise.
Attachments
IMHO MP3 will go away soon.
There is no marketing advantage to compression now that the internet is so fast and storage space is so great.
I think market forces will produce better quality.
There is really nothing else to offer.
Better hurry and smarten up the masses so they even know there is a difference. I have a different take, the technology will get so cheap that the high end will be able to separate and maintain its own agenda and be able to sustain itself and no longer rely on any financial input or consequence from the mainstream.
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Lower than the capacitance measured on a bridge with no DC applied. So if you had a 400 PIV diode that measure 25 pF and a 1000 PIV diode that measured 18 on the bridge. In a real power supply at 80 Vdc (160 PIV) the 1000V diode would still have lower capacitance than the 400V unit.
Hello Scott, let us put away marketing BS (DSP)
Now please check my questions without paying attention to expenses
Walter Jung proposed very good voltage regulators many years ago. They have 10nV/sqrtHz noise or better. Taking into account that PSRR in opamps is more than 40dB in audio range, will you put Walter’s regulators in your own audio system or will use LM317/337?
Victor swapped thick film resistors with metal film ones in his low distortion oscillator (discussed in different thread). 2nd and 3rd harmonics became 2-4dB lower. The distortion level is below -120dB and most of all isn’t audible, will you use thick film or metal film resistors in your audio system?
Keith Johnson measured cables with his test rig. He found that some cables produce larger jitter than others. Jitter caused by cables is considered as a marketing BS, but which cable will you use in your own audio system, good or better?
Scott Wurcer designed the opamp. This opamp has the additional pin to reduce distortion by extra 10dB at low gain at ultrasound frequencies. The distortion of the opamp is already below the hearing limit, will you add one more cap for distortion reduction trick in your own audio system?
Scott, I wish it would but you can see all these years that the high end doesn’t touch cheap technology. It is against it’s public image.
IMO the only cheap technology that touched the chicks of hi-end was LM1875
D but no )George
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Thanks. I know the grounds are tied together in various way but that is not what i was refering to. There have been recent changes to the NEC (within 5-10 years is recent to me) regarding HOW it is done. The aspect I am discussing relates to grounds and lightning and how it was mitigated via revised grounding practices.
The 6 volt grnd potential difference is way too high. More like < 6 tenths would be a better goal.
Thx-RNMarsh
IMO the only cheap technology that touched the chicks of hi-end was LM1875
Abby -
It was in the dressing and the $$$ check
-Normal
George
If you're building an instrument it is a different story. If we relied on audio custoners we would be broke.
I suspect it is the actual practice catching up to the code changes. There were items considered good practice on the California licensing test when I took it, that are now specifically banned in the NEC.
Now lightning protection is a bit of a different issue. In some areas the neutral is the top wire on the poles. Others it is in the middle. When it is in the middle you hear stories of how a lightning strike mysteriously took out half of the stuff in a house but amazingly didn't touch...
Where the neutral is on top it is a much bigger issue. Part of that is because many utilities use auto transformers to step down the HV to 220. If you lose the neutral, then all the line voltages go up. So what was thought to be a better way works to a point and then really zaps you.
The requirements have changed to three ground points, some of which may be cold water pipes but at least one driven ground rod and in some areas two.
Around here the telephone and cable companies always used the same ground when easy. So I wouldn't notice a change.
What I did notice is the requirement for arc interrupting circuit breakers wherever it is not a GFI. (Now you have mentioned you see almost all your line noise as in house sources, around here we have a clear channel AM station that can trip GFIs and arc interrupters! Also noise from the power companies data system.)
So what is a change where you live may not be much of one elsewhere. Remember the NEC is a guide that although used by many is not the only code throughout the country!
6 volts is a noise level balanced pro gear can live with. High End is quite different!
actually it appears ADI nearly went broke in the early 90's - while improving product quality, reducing production cost
Analog Devices Paper -- Quality Improvement Paradox
Whether you have noise coming from a local AM broadcast station has no bearing on home equipment also producing noise on the ac line. All audio-video-computer systems in the home produce unwanted frequencies/interference onto the ac power lines. All need individual isolated noise filters. All may not need AM filtering on the incoming ac power lines. Thx-RNMarsh
My take is that cheap technology has always been capable of excellent sound, but it has to be correctly engineered for this to happen. So, off the shelf low cost gear never sounds up to scratch because silly, and sometimes ridiculous, shortcuts are taken; generally the only solution in this case is for the individual to apply intelligent tweaking to get a good result. Which, of course, is effectively a very expensive solution ...
Once better understanding slowly filters through to those who count, and the desire by the "great unwashed" for something significantly above mediocrity builds, then things can happen ...
Frank
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