I've read a number of posts on here regarding this issue, with excellent input in particular by forum member AndrewT.
I'm somewhat confused about how to put it into practice. I've heard a number of different recommendations that are quite different, which concerns me.
Here is a photo of the preamplifier in question:
Link to full resolution image
Please note the boards are not populated/ this is not complete, I just posted the photo for a general reference of this design / sometimes understanding is easier with a visual example.
I'm on US Voltage and the transformer provides 260V & 6.3V AC, after the power supply the B+ is at 285.
So, there are 5 ground locations, numbered here:
#1 is chassis ground
#2 is power supply ground (no symbol just "GND", hidden by the cap)
#3 is the ground at the input of the preamplifier (Symbol is Earth Ground)
#4 is the signal ground - all of the signal grounds have been linked together, but not linked to any other numbered ground points.
#5 is for the ground cable from the tonearm. It is isolated from the chassis.
None of the grounds are currently attached to one another.. Just a little cable has been run.
From what I understand, the most critical for safety is that the incoming Ground from the IEC must be attached directly to chassis permanently, so that's non-negotiable.
Aside from this I've seen a number of different methods of tying the different grounds together with thermistors, diodes, resistors and caps in various configurations. I've seen anything from 10R to 120R suggested at a number of different wattages.
I'd like to minimize the potential for noise getting into the circuit, install a ground lift switch to avoid ground loops and also use best safety practice and I'm a little confused as to how to do so.
Here is where I'm still unclear:
1. Some have suggested also an IEC medical type filter, however with the multitude of various options within that category I'm unsure which is the best solution. Is there a configuration or model # which would be most useful for audio purposes? Could someone make a recommendation?
2. Would using this IEC filter remove the need for an X2 cap across the power switch to avoid power on/off noise?
3. If using an X or Y capacitor from the power supply ground to chassis ground does it need to be rated above 250V as it's after the transformer?
4. My assumption is that the ground lift should ONLY lift #5 Tonearm Ground from #1 Chassis Ground, is this correct?
5. My other assumption is that all of these ground points should be always connected in some way with the exception of the above. Is this also correct?
6. How can I ideally link all of these ground points while also rejecting noise? My assumption from what I've read is an x2 cap of 100nf and resistor of 10-50R 1/4W between Power Supply ground and Chassis Ground, and possibly all of these other ground locations? Since the power supply ground is linked to all of this do I need a higher rating than 250V at each location?
7. It doesn't seem likely that all ground points will need this filter between them.. if this is so, which are most in need of them?
Would appreciate some cut and dry recommendations as everything I have read has been rather general... prob. owing to the vast differences between different designs.
I understand that this is about learning and sometimes more general feedback is given to prompt further research, but since this relates to personal safety if you could please give specific values, types and ratings with any recommendations that would be appreciated.
I'm somewhat confused about how to put it into practice. I've heard a number of different recommendations that are quite different, which concerns me.
Here is a photo of the preamplifier in question:
Link to full resolution image
Please note the boards are not populated/ this is not complete, I just posted the photo for a general reference of this design / sometimes understanding is easier with a visual example.
I'm on US Voltage and the transformer provides 260V & 6.3V AC, after the power supply the B+ is at 285.
So, there are 5 ground locations, numbered here:
#1 is chassis ground
#2 is power supply ground (no symbol just "GND", hidden by the cap)
#3 is the ground at the input of the preamplifier (Symbol is Earth Ground)
#4 is the signal ground - all of the signal grounds have been linked together, but not linked to any other numbered ground points.
#5 is for the ground cable from the tonearm. It is isolated from the chassis.
None of the grounds are currently attached to one another.. Just a little cable has been run.
From what I understand, the most critical for safety is that the incoming Ground from the IEC must be attached directly to chassis permanently, so that's non-negotiable.
Aside from this I've seen a number of different methods of tying the different grounds together with thermistors, diodes, resistors and caps in various configurations. I've seen anything from 10R to 120R suggested at a number of different wattages.
I'd like to minimize the potential for noise getting into the circuit, install a ground lift switch to avoid ground loops and also use best safety practice and I'm a little confused as to how to do so.
Here is where I'm still unclear:
1. Some have suggested also an IEC medical type filter, however with the multitude of various options within that category I'm unsure which is the best solution. Is there a configuration or model # which would be most useful for audio purposes? Could someone make a recommendation?
2. Would using this IEC filter remove the need for an X2 cap across the power switch to avoid power on/off noise?
3. If using an X or Y capacitor from the power supply ground to chassis ground does it need to be rated above 250V as it's after the transformer?
4. My assumption is that the ground lift should ONLY lift #5 Tonearm Ground from #1 Chassis Ground, is this correct?
5. My other assumption is that all of these ground points should be always connected in some way with the exception of the above. Is this also correct?
6. How can I ideally link all of these ground points while also rejecting noise? My assumption from what I've read is an x2 cap of 100nf and resistor of 10-50R 1/4W between Power Supply ground and Chassis Ground, and possibly all of these other ground locations? Since the power supply ground is linked to all of this do I need a higher rating than 250V at each location?
7. It doesn't seem likely that all ground points will need this filter between them.. if this is so, which are most in need of them?
Would appreciate some cut and dry recommendations as everything I have read has been rather general... prob. owing to the vast differences between different designs.
I understand that this is about learning and sometimes more general feedback is given to prompt further research, but since this relates to personal safety if you could please give specific values, types and ratings with any recommendations that would be appreciated.
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Use a common ground point and connect all grounds to it, in a star configuration.
What are those silly red paint tins supposed to do, increase signal noise and bleed-over?
Use capacitors on the board as per the design of the board.
If you want a ground lift system, use a pair of 1n5401 diodes to stop voltage above 0.7v approximately both ways and a 100R with 100nF across them. No need in a well designed system but do what ever if you want.
As you write, earth and first ground should be one and the same on the chassis. Ground 2 can be after the diode RC network.
The reason for IEC IMO filters in equipment is to stop noise from your power supply entering the mains grid network. As it looks like you have a transformer diode arrangement and not SMPSU you don't get any benefit from one apart from aesthetics.
What are those silly red paint tins supposed to do, increase signal noise and bleed-over?
Use capacitors on the board as per the design of the board.
If you want a ground lift system, use a pair of 1n5401 diodes to stop voltage above 0.7v approximately both ways and a 100R with 100nF across them. No need in a well designed system but do what ever if you want.
As you write, earth and first ground should be one and the same on the chassis. Ground 2 can be after the diode RC network.
The reason for IEC IMO filters in equipment is to stop noise from your power supply entering the mains grid network. As it looks like you have a transformer diode arrangement and not SMPSU you don't get any benefit from one apart from aesthetics.
You have a thing called #4 signal ground. This appears to combine the input signal ground and the output signal ground. If so, separate these. The input sockets ground goes to the preamp input ground #3; the output sockets ground goes to the preamp output ground. This latter also connects to PSU ground #2 - assuming that this is at the output of the PSU: the clean end, not the dirty end.
The tonearm ground #5 is more a safety ground than a signal ground so it should go to the chassis, but not at the same point as the IEC safety ground attaches.
Don't put an X2 cap across the power switch. Put it across the transformer primary. If you use a mains filter then this cap may not be needed.
If you use a ground lift then this should go between the signal ground (i.e. preamp output plus PSU ground) and chassis. However, first try putting a piece of wire in. This is safer and you might have low hum. Don't scatter capacitors all over the place. They don't ground anything, they don't 'reject noise'. Much of what you read online about grounding is pure nonsense. Safety comes first - so various forms of ground lift should only be used a last resort. Then the aim is to provide signal reference potentials (as a voltage is always between two points) while at the same time avoiding injecting noise.
The tonearm ground #5 is more a safety ground than a signal ground so it should go to the chassis, but not at the same point as the IEC safety ground attaches.
Don't put an X2 cap across the power switch. Put it across the transformer primary. If you use a mains filter then this cap may not be needed.
If you use a ground lift then this should go between the signal ground (i.e. preamp output plus PSU ground) and chassis. However, first try putting a piece of wire in. This is safer and you might have low hum. Don't scatter capacitors all over the place. They don't ground anything, they don't 'reject noise'. Much of what you read online about grounding is pure nonsense. Safety comes first - so various forms of ground lift should only be used a last resort. Then the aim is to provide signal reference potentials (as a voltage is always between two points) while at the same time avoiding injecting noise.
IEC filter is usually only necessary for EMI compliance, e.g. if your cirucit don't use a microcontroller you do not need an IEC medical (or whatever) filter.
No, the X and Y caps *are* the filter in conjuction with a common mode
coil.
If you use a ready-made filter, the X and Y caps are already integrated into the filter.
X and Y caps comply to safety standards. See wikipedia.
Don't use a groundlift. This are usually hacks to circumvent bad grounding.
If your tonearm is floating, ground lift is useles anyway.
Yes, otherwise these points are not GROUND.
If you use Class I construction, the standard is very clear:
Any touchable part MUST be grounded including connectors.
Why spend so much thought about problems which will not even manifest itself?
I suggest, stop writing, start building 🙂
Reality is much simpler: connect your circuit ground to chassis with a solid
bolt and that is it.
There is no playground here: Connect each metal part with a solid cable to chassis ground. Nothing to discuss here.
In some cases of large installations or very bad ground layout you could gain a few dB im Noise, but with Vinyl (and mostly with CD too) the SNR is so bad, that this is not audible.
Udo
These things definitely are worth thinking about, as more than exactly one device with signal ground tied to PE in any setup using unbalanced interconnects = guaranteed trouble.
This case is a bit tricky because having high voltages really suggest Class I. Obviously there's always the brute-force (if expensive) way of solving it, going transformer-coupled on all the ins and outs (well, save for the phono input including tonearm ground).
Plan B would be floating the entire amplifier circuitry, requiring Class II level precautions around the primary side, insulated standoffs, plastic knobs and so on (capacitive coupling in the transformer should also be low enough not to cause substantial leakage currents, but in the 20-30 VA vicinity or below as commonly found in preamps, this is usually the case even in toroidals). Output coupling caps should also be able to sustain maximum supply voltage.
So there's two separate problems to solve here really, (a) find a good grounding scheme for the audio signal, and (b) reconcile grounding and earthing concerns.
This case is a bit tricky because having high voltages really suggest Class I. Obviously there's always the brute-force (if expensive) way of solving it, going transformer-coupled on all the ins and outs (well, save for the phono input including tonearm ground).
Plan B would be floating the entire amplifier circuitry, requiring Class II level precautions around the primary side, insulated standoffs, plastic knobs and so on (capacitive coupling in the transformer should also be low enough not to cause substantial leakage currents, but in the 20-30 VA vicinity or below as commonly found in preamps, this is usually the case even in toroidals). Output coupling caps should also be able to sustain maximum supply voltage.
So there's two separate problems to solve here really, (a) find a good grounding scheme for the audio signal, and (b) reconcile grounding and earthing concerns.
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