I have been trying to find out why you would want to supply an amplifier with a ground lift achieved by a 100R resistor in series from chassis (earthed) to circuit 0v?
My power amp has this and my preamp does not. So of course the preferred return will be via the preamp input leads ground rather than the 100R to the chassis and earth on the power amp mains plug?
I have successfully reduced a bit of hum on my preamp and also had an unexpected increase in sound quality trying a low impedance earth connection like this article suggests - basically taking the circuit earth through a separate low impedance connection. (2 plugs on one amp)
http://tech.juaneda.com/en/articles/Ground_and_safety_earth.pdf.
I was going to try the same approach on the power amp, and discovered the 100R lift and wanted to understand why you would do this, and does it need to be part of a system approach, meaning you would want to do the same with the preamp if the 'lift' was for some reason preferred?
Thanks,
My power amp has this and my preamp does not. So of course the preferred return will be via the preamp input leads ground rather than the 100R to the chassis and earth on the power amp mains plug?
I have successfully reduced a bit of hum on my preamp and also had an unexpected increase in sound quality trying a low impedance earth connection like this article suggests - basically taking the circuit earth through a separate low impedance connection. (2 plugs on one amp)
http://tech.juaneda.com/en/articles/Ground_and_safety_earth.pdf.
I was going to try the same approach on the power amp, and discovered the 100R lift and wanted to understand why you would do this, and does it need to be part of a system approach, meaning you would want to do the same with the preamp if the 'lift' was for some reason preferred?
Thanks,
To prevent ground loops
As you pointed out, the amp is grounded through the preamp. Thus no ground loop. Improving the grounding of the preamp should improve the hum. Taking out the 100R resistor is likely to create hum as you will be creating a ground loop.
As you pointed out, the amp is grounded through the preamp. Thus no ground loop. Improving the grounding of the preamp should improve the hum. Taking out the 100R resistor is likely to create hum as you will be creating a ground loop.
Be aware that if you've separated signal ground from safety ground by 100R, you have defeated the safety ground. It works by tripping the house breaker. Please don't do things like this without some basic safety considerations. Safety is not about you - it's about family, friends, pets.
YOS,
Chris
YOS,
Chris
Easy: somebody designed something that passes both dirty currents (like charging first filter cap pulses) and an input (or line level output) signal through a ground loop. Why? Because do not understand that wires, even thick wires, have resistance and currents cause voltage drops on them.
Solution? Either discard that boutique amp or preamp, or try to eliminate the consequence of the wiring error "lifting" a ground. Bogus, yes, but works. However, such gear would never pass UL certification, so in order to mitigate the problem, such "lifting" resistors are shunted by reverse parallel diodes.
"Ground loops" are innocent. Guilty are people who do not understand how they contaminate ground loops.
Solution? Either discard that boutique amp or preamp, or try to eliminate the consequence of the wiring error "lifting" a ground. Bogus, yes, but works. However, such gear would never pass UL certification, so in order to mitigate the problem, such "lifting" resistors are shunted by reverse parallel diodes.
"Ground loops" are innocent. Guilty are people who do not understand how they contaminate ground loops.
Just to correct here, in the interests of safety and for future reference, this is untrue.
If protective earth is connected to the chassis, the fault loop still exists for when an active conductor comes in contact with the chassis (and therefore people), assuming the fault loop impedance is low enough (all considerations external to the amplifier and specific to the installation) then the circuit breaker will disconnect the supply.
Referencing of signal common to mains earth is completely irrelevant for safety purposes, ie. stacked and floating supplies do this all the time.
SM
"If protective earth is connected to the chassis, the fault loop still exists for when an active conductor comes in contact with the chassis (and therefore people), assuming the fault loop impedance is low enough (all considerations external to the amplifier and specific to the installation) then the circuit breaker will disconnect the supply."
By "active conductor" here you must mean either line or neutral in the primary circuit, because everything on the secondary side is at least 100R from chassis. To be able to throw a home sized breaker, this is too much R. If the ground lifted device were isolated, and not connected to anything else with safety grounds, you'd have a stronger point, but that can't be assumed.
As Wavebourn has said, the safe solution is the 35A bridge doubled-doubled diode. And even this is scary.
YOS,
Chris
By "active conductor" here you must mean either line or neutral in the primary circuit, because everything on the secondary side is at least 100R from chassis. To be able to throw a home sized breaker, this is too much R. If the ground lifted device were isolated, and not connected to anything else with safety grounds, you'd have a stronger point, but that can't be assumed.
As Wavebourn has said, the safe solution is the 35A bridge doubled-doubled diode. And even this is scary.
YOS,
Chris
Last edited:
Thanks everyone,
So my take on this is the safety earth operates as normal from the chassis to earth and will operate conventionally as it is unimpeded.
The circuit ground in the power amp is lifted by 100R from the chassis earth of the power amp, BUT the chassis earth of the preamp is NOT lifted so the easiest path to earth (lowest resistance) is via the phono leads earth back into the preamp.
I have 3 options in my opinion, all of which are safe I think
1. Leave alone - the majority of the return for the Power Amp is via the Preamp due to the 100R
2. Lift the Preamp in a similar manner - But I still don't know WHY I would benefit, the lift is a standard approach for this amplifier manufacturer for both pre and power amps (high end tube)
3. Remove the 100R it creates a 2nd pathway and has the potential to create a subsidiary loop.
Thoughts
So my take on this is the safety earth operates as normal from the chassis to earth and will operate conventionally as it is unimpeded.
The circuit ground in the power amp is lifted by 100R from the chassis earth of the power amp, BUT the chassis earth of the preamp is NOT lifted so the easiest path to earth (lowest resistance) is via the phono leads earth back into the preamp.
I have 3 options in my opinion, all of which are safe I think
1. Leave alone - the majority of the return for the Power Amp is via the Preamp due to the 100R
2. Lift the Preamp in a similar manner - But I still don't know WHY I would benefit, the lift is a standard approach for this amplifier manufacturer for both pre and power amps (high end tube)
3. Remove the 100R it creates a 2nd pathway and has the potential to create a subsidiary loop.
Thoughts
If that's your take from my comments, then I've failed to explain the situation adequately and you're dangerously mistaken.
YOS,
Chris
YOS,
Chris
Hi Chris, I understand your concerns about this solution for seperating circuit ground from safety earth. Is the only solution that you would condone the removal of the ground lift resistor?
There are times where there should be a single version of the truth since there are lots of opinions about how this should be done. Maybe there should be a sticky thread covering grounding?
Having looked at lots of consumer 60's amplifiers, they generally adopt a 'ground plane' approach, with multiple grounding points. The tube bases had 4 ground lugs, for example, and a grounded centre 'shield'. Is this just a flawed solution that will never defeat the noise in our modern power supplies?
Cheers, Richard
There are times where there should be a single version of the truth since there are lots of opinions about how this should be done. Maybe there should be a sticky thread covering grounding?
Having looked at lots of consumer 60's amplifiers, they generally adopt a 'ground plane' approach, with multiple grounding points. The tube bases had 4 ground lugs, for example, and a grounded centre 'shield'. Is this just a flawed solution that will never defeat the noise in our modern power supplies?
Cheers, Richard
ooops well I have obviously misunderstood.
The earth lift on the Power amp is as supplied and not my work or modification. The preamp is connected as supplied to earth, the only modification I have done to the preamp is to ADD an additional earth line to take some noise out of the signal circuit, which seemed to work.
Normally the 100R would not be in place I assume in an amplifier without a lift, and would simply be a conductor of low resistance.
If you have a double insulated product that has not an integrated chassis earth the signal ground is taken from the connected devices, so my simplistic logic was if the Earth is still to chassis on the Power amp the safety is still in place, and so how the signal ground is configured is no longer part of the same safety story?
Thanks again, and agreed I don't want to do anything unsafe.
Confirming: If mains earth is connected unimpeded to conductive chassis = no problem. In other words, conductive chassis must be connected to mains earth.
SM
Last edited:
Chassis is at 0 volts.
Transformer primaries should be fused locally (at the chassis).
We need to make distinction between ground (mains earth) and signal common (which can be floated).
SM
Ok - this makes sense - thanks.
So the question I am still struggling to answer is what would be the benefit of lifting the Signal Common? Why is this an advantageous approach, and presumably this would only work in real terms if all components connected were similarly lifted.
100R 'lift' would presumably increase the Signal common voltage......until it was connected to a preamp without any lift.....
Just confused as to Why .....this is done to be a preferred approach
Got a schematic?
Only lifts voltage if there is current flowing.
AKSA amplifier used to (still do?) the same thing.
Something to do with noise but I never found need to do it, think about where the current flows, you can isolate signal return from mains earth this way (depending on other connected equipment).
If it doesnt need to be stacked or floating, tie signal common to mains earth at the lowest ripple point (yeah, I know.. its 0V right?.. ), try the final filter cap, or last shunt element (in case of regulated supply) - and not CT of the secondary (if you use one), something to do with the return path of current charging pulses, smoother waters at the end of the supply (apparently).
SM
Only lifts voltage if there is current flowing.
AKSA amplifier used to (still do?) the same thing.
Something to do with noise but I never found need to do it, think about where the current flows, you can isolate signal return from mains earth this way (depending on other connected equipment).
If it doesnt need to be stacked or floating, tie signal common to mains earth at the lowest ripple point (yeah, I know.. its 0V right?.. ), try the final filter cap, or last shunt element (in case of regulated supply) - and not CT of the secondary (if you use one), something to do with the return path of current charging pulses, smoother waters at the end of the supply (apparently).
SM
Last edited:
Sorry no schematic, it's a 211 amplifier that is a one-off build 20 years ago from an amplifier builder/brand who it seems still uses this lift approach.
I am tempted to find the 100R disconnect and then run a low impedance Signal Ground to another wall socket as per my preamp where it helped.
This covers everything just about - http://www.valvewizard.co.uk/Grounding.pdf . Inna nutshell a resistor from your ground bus to your chassis reduces any high current that may be flowing through said gnd bus to chassis.
Andy.
Andy.
Connect signal common to mains earth at the end of the B supply negative (and no where else, which includes the wall socket).
Picture zero volts, picture you in a boat.. the return current is 'most calm', where?.. waterfall, or outlet to sea? ;-)
Now add 10R 🙂
SM
Last edited:
To take your second part first: yes! there's a need for a good resource for mains wiring safety for DIYers. There's lots of well intended but wrong advice on the Great Interweb.
On your third point: signal grounds are a horse of a whole different religion than safety grounds, and they often conflict. Noise on signal grounds is easily defeated by simply not believing in "grounds". No such critter exists, unless you're falling off a ladder.
And on your main topic: there were several approaches to this issue taken over the years. In olden times, when men were men, and lives were cheap, 2 wire power cords (now called Class 0) relied on everything touchable being insulated. Later Class 1 added a safety ground to "earth". Newest is Class 2, double insulated, so that no single point of failure can cause injury. This is great from an audio system perspective because it causes no safety earth ground loop.
For DIYaudio, normally a system can be arranged so that all of its safety grounded parts can be plugged into the same power strip. Ideally, everything into the same strip, and if an outlander like a TV or antenna cable must be accomidated, its shield (presumed to be properly earthed before entering a building) is bonded to this strip's safety earth. (This is normally done inside power strips with f-connectors).
This local power strip/safety ground junction localizes safety ground loops enough for essentially all cases. For the rare cases where it's not sufficient, separation of signal from safety grounds is needed, or the system needs rethinking. In no case can safety be secondary. Rant mode off.
Chris
Indeed. Why all the strurm und drang about separating signal "ground" from safety "ground"? If there weren't a safety issue, why would they ever have been connected in the first place? Pretty fair question, I'd say.
All safety issues derive from you(r loved one) not being a bird on a wire. You(r loved one) has to contact something faulted to dangerous voltage (from earth) and also something nominally earthed. Safe practice requires always assuming the second part.
Best practice for DIY and for restoration of antiques is to try to meet Class 1 standards, with line and neutral floating, fusing and switching in the "line", nothing in the neutral, and safety earth to chassis with a dedicated bolt.
Now to the signal "ground": signal should (ideally) travel over a close pair of conductors and over no other paths. When signal "grounds" are significantly connected to safety "grounds" several paths appear, in parallel. For example, preamp A is connected with RCAphono cables to power amplifier B, and both have Class 1 safety grounds and their signal grounds connect to safety ground. You can see that each signal channel has one "hot" inter-chassis connection and three return ("ground") connections - the two interconnect returns plus safety ground.
IOW, far from the one-and-only-one ideal. But, how big of an issue is it? Consider that if there were no safety grounds (or they were safely isolated from signal) each signal channel will still have one "hot" conductor and two returns. Still far from ideal, but almost the universal case. So, keep everything together, one power strip, maybe look at differential inputs down the road.
All good fortune,
Chris
Last edited:
