Hi All!
I'm building an RH84 and have grounded it as follows: AC line green direct connection to chassis very close to IEC socket, all else star-grounded back to PT secondary. Upon checking continuities, I realized my secondary grounds are all isolated from the chassis ground (all my star-ground connections used insulated terminal strips). Is this an absolute no-no? What are the pros/cons of doing this? Thanks!
I'm building an RH84 and have grounded it as follows: AC line green direct connection to chassis very close to IEC socket, all else star-grounded back to PT secondary. Upon checking continuities, I realized my secondary grounds are all isolated from the chassis ground (all my star-ground connections used insulated terminal strips). Is this an absolute no-no? What are the pros/cons of doing this? Thanks!
I think the main con is that your chassis will not be as effective as a shield if you audio ground is not shared with chassis ground at one point. You're in a good position if you've built your power supply and audio circuits such that they are completely isolated because you can choose exactly how to do it. In some guitar amps, the circuit is referenced to chassis ground at the input, directly from the ground of the cathode resistor of the input stage.
But grounding is the black art of amp building. I'm aware of several other ideas, like making that ground through a resistor, etc... I'm not representing my answer as complete.
But grounding is the black art of amp building. I'm aware of several other ideas, like making that ground through a resistor, etc... I'm not representing my answer as complete.
That is dangerous, there should be a connection between the audio ground and the metal chassis.
However, the connection could be a low value resistor and/or a diode bridge.
Yes, very dangerous. Consider that your input jack's shield connection is floating above earth ground (Protective Earth) by some unknown amount of leakage. Then, consider that the chassis and signal grounds of all of your sources (which might include video or other devices with a distant-but-real earth ground) are separated from the amplifier's chassis by the interconnecting cables.
You hold the chassis at one end of the interconnecting cables with one hand to steady it when plugging in the cables. First end, no drama Mama. Second end, you (or a loved one) has the leakage current hand to hand. Even small risks to other people, if avoidable, are not forgivable. Nobody cares about you - your friends will look sad for a few weeks and then come sniffing around the pretty widow. But just don't.
As rayma has said, there are safe ways to isolate signal grounds from chassis, which must! connect directly to Protective Earth. Try a simple hard wire first, but if you have ground loop issues, investigate the various isolation schemes, all intended to give a high enough (even 10R is enough) impedance between signal ground and PE, but a low enough impedance in emergency-level failures to keep folks unhurt.
All good fortune,
Chris
You hold the chassis at one end of the interconnecting cables with one hand to steady it when plugging in the cables. First end, no drama Mama. Second end, you (or a loved one) has the leakage current hand to hand. Even small risks to other people, if avoidable, are not forgivable. Nobody cares about you - your friends will look sad for a few weeks and then come sniffing around the pretty widow. But just don't.
As rayma has said, there are safe ways to isolate signal grounds from chassis, which must! connect directly to Protective Earth. Try a simple hard wire first, but if you have ground loop issues, investigate the various isolation schemes, all intended to give a high enough (even 10R is enough) impedance between signal ground and PE, but a low enough impedance in emergency-level failures to keep folks unhurt.
All good fortune,
Chris
Don't use the direct connection as it won't be optimal causing ground loops. You can only use a direct connection if the other devices in the chain have "lifted" arrangements. Unless they're DIY they normally have direct connections....or no connection at all with classII devices. It would take a small investigation to check what you have.
The 10 Ohm 2W/diode bridge/thermistor solutions really are to be preferred.
The 10 Ohm 2W/diode bridge/thermistor solutions really are to be preferred.
Connecting all exposed chassis metal to the IEC socket Earth ground is a must. Ideally you want your signal ground to be at Earth potential as well. The real problem with ground loops tends to be from other equipment connected to your amp that also uses a three wire power connection. In some of these instances you MAY need a ground lift switch on the auxiliary piece of equipment. Or you can also use a simple line level isolation unit. You can build these yourself or buy one relatively inexpensively.
The bottom line is you really need to develop a grounding philosophy which promotes both safety and fidelity. Then you need to stick to it. Something like this: https://www.cascadetubes.com/2020/01/13/grounding-philosophy/ may be helpful.
The bottom line is you really need to develop a grounding philosophy which promotes both safety and fidelity. Then you need to stick to it. Something like this: https://www.cascadetubes.com/2020/01/13/grounding-philosophy/ may be helpful.
"Lifting" safety grounds is dangerous and foolish. Issues with Protective Earth (PE) ground loops need to be dealt with another way. For the vast, vast majority of home audio systems this requires only that they have all of the system's electronics plugged into the same power outlet strip. This keeps the PE ground loop small and local. In the worst case of a separate remote Earth ground in a video cable system, that incoming cable needs its shield to be Earthed to the power strip. (Commercial power strips with F-connectors do this internally, but it can be done externally).
Large room professional installations deal with these issues in different ways (differential inputs, sometimes floating), but disabling of safety (PE) grounds is never allowed. Small room home installations are easily tamed with a single power strip in essentially all cases. Those folks worried about the remnant ground loop current can isolate signal "ground" from PE with 10R in parallel with some back-to-back diodes properly sized to throw a breaker. Never "lift" PE grounds if a three wire outlet is available.
All good fortune,
Chris
Large room professional installations deal with these issues in different ways (differential inputs, sometimes floating), but disabling of safety (PE) grounds is never allowed. Small room home installations are easily tamed with a single power strip in essentially all cases. Those folks worried about the remnant ground loop current can isolate signal "ground" from PE with 10R in parallel with some back-to-back diodes properly sized to throw a breaker. Never "lift" PE grounds if a three wire outlet is available.
All good fortune,
Chris
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I copied and pasted this from Tubecad issue #282. One of the methods mentioned here.
https://www.tubecad.com/2014/03/blog0282.htm
New House-GND Kit
The wall outlet's third jack connects to the house ground, which is also known as "earth," as the house ground is often created by attaching the wall socket's neutral connection to an 8-foot metal rod buried in the dirt under your house or to the cold-water pipe, assuming that the pipe is made of metal. Many old houses and apartment buildings do not offer a connection to the house ground, only the two power wires, which is unfortunate, as the a connection to the house ground is a safety feature.
For example, say that something goes terribly wrong in your power amplifier and the B+ attaches to the chassis. Well, if the chassis does not make a connection to the house ground, you could receive a lethal shock from touching the energized chassis. But with a solid connection made to the house ground, the B+ voltage would drain away safely.
The big problem for us audiophiles is that house ground often becomes contaminated by other electrical devices in your house. This could be avoided, if when they laid out the house wiring, each wall socket got its own separate house-ground wire that in a star-grounding fashion traveled independently back to the houses fuse box and its ground connection. But as this excellent setup would require much more wire, it is seldom performed; instead, most house-ground connections daisy chain their way back to the electrical panel's house ground, much like Christmas-tree lights strung in series. Some electrical equipment is miswired internally, so the neutral and house-ground connections are reversed. This causes something which should never occur: the house-ground wire seeing a sustained current flow.
(Ham-radio operators face much more dangerous situations, as lightning can hit the transmitting antenna and then travel through the house wiring until it hits the house ground, setting your house ablaze along the way.)
How do you know if you have a dirty house ground connection? Simply attach an AC volt meter to the neutral and house ground connections on the wall socket and read the voltage. It should read 0V. In my listening room, it doesn't, as there is a 500mV AC voltage difference between the two. Is that a problem? Not if you plug a lamp or a toaster into the wall socket, but it is if you plug in some audio equipment, as the resulting hum testifies loudly.
The workaround is to use the following circuit.
The wall outlet's third jack connects to the house ground, which is also known as "earth," as the house ground is often created by attaching the wall socket's neutral connection to an 8-foot metal rod buried in the dirt under your house or to the cold-water pipe, assuming that the pipe is made of metal. Many old houses and apartment buildings do not offer a connection to the house ground, only the two power wires, which is unfortunate, as the a connection to the house ground is a safety feature.
For example, say that something goes terribly wrong in your power amplifier and the B+ attaches to the chassis. Well, if the chassis does not make a connection to the house ground, you could receive a lethal shock from touching the energized chassis. But with a solid connection made to the house ground, the B+ voltage would drain away safely.
The big problem for us audiophiles is that house ground often becomes contaminated by other electrical devices in your house. This could be avoided, if when they laid out the house wiring, each wall socket got its own separate house-ground wire that in a star-grounding fashion traveled independently back to the houses fuse box and its ground connection. But as this excellent setup would require much more wire, it is seldom performed; instead, most house-ground connections daisy chain their way back to the electrical panel's house ground, much like Christmas-tree lights strung in series. Some electrical equipment is miswired internally, so the neutral and house-ground connections are reversed. This causes something which should never occur: the house-ground wire seeing a sustained current flow.
(Ham-radio operators face much more dangerous situations, as lightning can hit the transmitting antenna and then travel through the house wiring until it hits the house ground, setting your house ablaze along the way.)
How do you know if you have a dirty house ground connection? Simply attach an AC volt meter to the neutral and house ground connections on the wall socket and read the voltage. It should read 0V. In my listening room, it doesn't, as there is a 500mV AC voltage difference between the two. Is that a problem? Not if you plug a lamp or a toaster into the wall socket, but it is if you plug in some audio equipment, as the resulting hum testifies loudly.
The workaround is to use the following circuit.
The diode bridge only connects the two grounds when the voltage difference between them exceeds about +/-1.4V. The capacitor allows high-frequency noise to find a path to the house ground. The 10-ohm power resistor makes a DC connection between grounds, while still offering some isolation between grounds.
As can be seen from these photos, the new GlassWare House GND kit is quite small, the PCB being only 1 by 1.4 inches big. The House GND kit is available now at the GlassWare-Yahoo store for the stupidly inexpensive price of $9.95. Why so cheap? I needed these kits myself, so made extra PCBs, as knew others need them as well.
Some of the explanation (about "contamination") seems a little garbled, but the solution is correct. Nowadays, a 35 Amp rectifier bridge is recommended, to insure survival long enough to throw the breaker in worst case failures. Because it's protected by the diodes, even a very small wattage resistor is fine. But even this solution is most often not needed if the PE ground loop is kept small and local. Specific situations vary, so it's good to know of this solution for extreme unction.
All good fortune,
Chris
All good fortune,
Chris
I picked up an analog Leader AC millivolt meter at a swap meet a while back... It will be interesting to measure how much potential exists between safety ground and neutral at various outlets in my home. The area where I have my AV receiver hums unless any source devices with a ground pin use a cheater. In that system my AV receiver must be the only thing safety grounded, all other sources have to ground via the interconnect. I probably have some millivolts between ground and neutral on that particular outlet. Of course that room has all kinds of alexas, blutooths, blu ray, computers, games, etc. a big hodge podge of entertainment sources.
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I work with a lot of musicians, and by far the main way that they get shocked is by becoming a ground path for AC leakage. For example, a guitar player may be singing into a microphone plugged into a PA system that is properly earth-grounded. But he's playing guitar through an old amp he's never had properly serviced, so it still has its original two-wire power cord and "death caps" that should be wired from chassis to AC neutral, but which have a 50/50 chance of being connected to AC hot. And then those caps are 60 years-old and leaky. He's connected to the chassis ground of his amp via his guitar strings, and his lips touch the metal mic screen. Bam. He gets shocked. Or it could be the other way around. His amp might be properly earth-grounded, but the PA system isn't. I suppose getting B+ to chassis could happen, as mentioned above, though I've never seen that occur. AC power leakage, though, is still quite common. Some older musicians are very cavalier about this and even scoff at younger musicians objections to being shocked. Even when you explain the danger to them, it seems not to sink in.
And some of these kitchen-table guitar amp builders who simply copy circuits without understanding them reinstall "death caps" because they don't know any better.
Even more insidious is AC leakage from the power transformer primary to the transformer laminations and bell-ends and, thus, to the chassis. It's a known issue in some old transformers, particularly those used by Ampeg. You should really run an AC leakage test on all old two-wire equipment before adding an earth ground, but few people know to do this.
As for me, personally, I live in a house built before 1960, and though the wiring is in good condition, my main HiFi system is located by necessity in a place that still has two-wire sockets. It's on the second story, and the floors are wood, so there's no easy way for me to become a ground path because there's no earth ground within reach. The kitchen and bathroom circuits were updated, but not the rest of the house.
And some of these kitchen-table guitar amp builders who simply copy circuits without understanding them reinstall "death caps" because they don't know any better.
Even more insidious is AC leakage from the power transformer primary to the transformer laminations and bell-ends and, thus, to the chassis. It's a known issue in some old transformers, particularly those used by Ampeg. You should really run an AC leakage test on all old two-wire equipment before adding an earth ground, but few people know to do this.
As for me, personally, I live in a house built before 1960, and though the wiring is in good condition, my main HiFi system is located by necessity in a place that still has two-wire sockets. It's on the second story, and the floors are wood, so there's no easy way for me to become a ground path because there's no earth ground within reach. The kitchen and bathroom circuits were updated, but not the rest of the house.
Does that system have a cable box? One often overlooked PE ground loop is the TV cable itself, which by code is Earthed before entering the house. Code usually requires using the same Earthing as AC power. Easily testable as an issue by simply unscrewing the cable. This ground loop can also be localized by connecting shield to PE (third wire). Some fancier power strips do this internally, but you can also do it externally. I'm assuming you already have everything plugged into a single power strip.
I've seen particularly sensitive systems with a lot of little switching power supplies have a small background buzz from the noise on the AC power. In those cases a second power strip containing some filtering can be fitted, for those noisy little widgets, and plugged into the main power strip, maintaining a small local PE loop. Please don't lift PE grounds where PE is available at the outlet.
All good fortune,
Chris
There is a "cable box" but I have 1 gigabit speed fiber optic (not analog coax) so only cat6 hooks into it with hdmi out and a wall wart. I have a Schitt DAC, the Schitt instructions specifically said to use a cheater if you get a loud 60hz hum, that's a commercial product telling you to use a cheater if needed! Fortunately only two source devices have a 3 prong plug, the Schitt and a Blu ray player. So only two cheaters. It is all on one power strip too.
Sounds like you're doing the best with the hand you're dealt. My house is too old to have any 3-wire outlets, so I have to improvise, but in a public forum, viewed by folks of lots of different experience levels, I feel bound to be extra conservative and safety minded. (Do what I say, not what I do).
Very surprising that those two modern pieces would have Class ! wiring, when everything modern seems to be moving to Class 2 (double insulated, no PE).
All good fortune,
Chris
Very surprising that those two modern pieces would have Class ! wiring, when everything modern seems to be moving to Class 2 (double insulated, no PE).
All good fortune,
Chris
Old house huh. Mine is 1995 so all 3 prongs, but the neutrals are shared all over the place to save on wire costs, not perfect. Old houses can be upgraded to have a proper ground bonding in a new breaker box, then from there all you'd have to do is run 3 wire Romex branch circuits to rooms as-needed over time. Kitchen and baths first, then run one to your audio gear! Good selling point later for the house.
Who said anything about lifting safety grounds?!? Earth grounding all exposed metal is a must.
Ground lifting (i.e breaking the in-equipment tie between the REQUIRED safety ground, which remains tied to Earth ground via the three wire cord, and the signal ground) is only for signal grounds when signal ground reference is provided by another piece of equipment.
Your post is completely correct, and to code. The "Grounding Philosophy" article seems to suggest otherwise, saying that safety grounding (PE) can be safely done through the interconnect cables - this part is not correct, or safe.
All good fortune,
Chris
All good fortune,
Chris
In my setup, audio ground is connected to earth at the chassis, and ground loops (The computer is on the same circuit as most of the audio, but connected to a TV which is connected to another computer on ther other side of the panel) are solved with AD/DA optical connections. Even my preamp has a variable optical out to feed the amps on the other wall. Isolation transformers are hit and miss here. Some equipment can't drive them, other times the isolation transformer adds hum from magnetic coupling of power circuits.
You SHOULD always ground your stuff, but 95% of the audio equipment for sale uses 2 pin power and double insulation.
Here's what I think of when I hear "Death Cap"... Don't use these in an amplifier, either.
"Amanita phalloides (/æməˈnaɪtə fəˈlɔɪdiːz/), commonly known as the death cap, is a deadly poisonous basidiomycete fungus."