My HPamp casing is coming along and I have to make arrangements to ground it with the 0 of the double supply.
I have 2 VHF transmitters nearby , cellphone tower at 800 m and nearby wifi to keep out.
It will be connected to my computer , but the ground of the signal is not the same as the metal outside of the computer case. I don't want to accidentally touch the HP casing against the computer's. Also it will be used on the bed with static electricity , and touching the HP casing is then touching the computer's audio output which I think is bridged. Of course I could spray paint or lacquer the aluminium casing , but that is not easy to do well and
after all the work I put in , I don't want to ruin it soaking it in solvent to get it off again.
So here's my question : Will grounding be affected if I connect it not directly to the 0 , the ground of the supply , but via a 10K to 100K resistor or even a 1M resistor ?
Also do openings for LED's , nylon bolts to connect the LM3x7 to the aluminum case for cooling or even a small plexiglass window for viewing the status LED's inside , affect the shielding much ?
I have 2 VHF transmitters nearby , cellphone tower at 800 m and nearby wifi to keep out.
It will be connected to my computer , but the ground of the signal is not the same as the metal outside of the computer case. I don't want to accidentally touch the HP casing against the computer's. Also it will be used on the bed with static electricity , and touching the HP casing is then touching the computer's audio output which I think is bridged. Of course I could spray paint or lacquer the aluminium casing , but that is not easy to do well and
after all the work I put in , I don't want to ruin it soaking it in solvent to get it off again.
So here's my question : Will grounding be affected if I connect it not directly to the 0 , the ground of the supply , but via a 10K to 100K resistor or even a 1M resistor ?
Also do openings for LED's , nylon bolts to connect the LM3x7 to the aluminum case for cooling or even a small plexiglass window for viewing the status LED's inside , affect the shielding much ?
10K will already severely affect the shielding: it will annihilate completely the RF protection, and significantly reduce the LF shielding effect.
For LF, you should stay well below 1K, depending on the exact circumstances, and it should be paralleled with a 10nF to 100nF capacitor for the RF.
The effect of the openings depends on their size and proximity with sensitive sections of the circuit.
You should not have to worry about a 3mm hole, but a window could be problematic.
Regarding RF, what counts is the perimeter of the opening: it should be significantly smaller than the shortest wavelength to be blocked
For LF, you should stay well below 1K, depending on the exact circumstances, and it should be paralleled with a 10nF to 100nF capacitor for the RF.
The effect of the openings depends on their size and proximity with sensitive sections of the circuit.
You should not have to worry about a 3mm hole, but a window could be problematic.
Regarding RF, what counts is the perimeter of the opening: it should be significantly smaller than the shortest wavelength to be blocked
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Thanks Elvee !
Staying below 1k , doesn't give me enough protection. Only a 100nF for RF (without the resistor) would be enough ?
LF is not much of a problem , the 50 Hz of the transformer is also in de casing.
Or maybe the dreaded spray paint with no little window.
Thanks.
Staying below 1k , doesn't give me enough protection. Only a 100nF for RF (without the resistor) would be enough ?
LF is not much of a problem , the 50 Hz of the transformer is also in de casing.
Or maybe the dreaded spray paint with no little window.
Thanks.
What type of mains power input socket you have on your HP amplifier? If the mains cable is not detachable, does it have a PE (protective earth) wire?
Protection against what?
A 100nF has a non-negligible conductance at audio frequencies, and allows the build-up of static charges if not shunted by a resistor
Non detachable mains cable encased in epoxy . No protective earth . It is not needed and I don't even have earthing in the wall outlets.
Protection against touching the computer casing with the HPamp.
1k is not goog enough for 2000 V ESD when touching the bare aluminium case.
Your computer is an IEC Class I appliance, meaning the case is connected to the protective earth. The HP amplifier is a Class II appliance, that is double insulated, and should no be earthed. The signal grounds of the two devices can be connected together, the interconnecting cable will provide signal ground continuity frome the computer (where the GND is connected to the protective earth) to the HP amp (where the GND is connected to the PSU 0, but isolated from the case). Touching the computer casing is safe, because it is earthed. Touching the HP casing is also safe, because it is double insulated. If the casing of the HP amp gets in contact with the casing of the computer, nothing happens. There is no ground loop or dangerous voltage. I think there is nothing to worry about, you are overthinking it.
Using a class I device in non-earthed conditions is a problem in itself.
If ESD frightens you, the solution is to use leakage resistors, not connected to PE since you don't have one, but to the mains. They need to have a safety rating equivalent to Y capacitors, but I don't know the exact terminology. I just know that they exist: they typically have a very elongated form-factor, to prevent an arc from jumping directly from one end to the other
If ESD frightens you, the solution is to use leakage resistors, not connected to PE since you don't have one, but to the mains. They need to have a safety rating equivalent to Y capacitors, but I don't know the exact terminology. I just know that they exist: they typically have a very elongated form-factor, to prevent an arc from jumping directly from one end to the other
I measured again , there where the paint of my 15 year old computer has worn off , indeed the ground of USB , firewire and audio are on the exposed casing and on the PE , which is not connected by me . This last one was a surprise , but I checked because Elvee hinted at this.
Normally you don't touch that on the computer (when there is no bare metal) , but now connecting the case of the HPamp , the inner ground of the computer , will always be touched when touching the HPamp. That's why I asked about putting a resistor between the case and the 0.
But that's a no go.
Icsaszar makes a good point though that if the power wire touches the casing , not only a shock but will destroy my computer.
The way I build , it is not exactly a Class II appliance ...
Normally you don't touch that on the computer (when there is no bare metal) , but now connecting the case of the HPamp , the inner ground of the computer , will always be touched when touching the HPamp. That's why I asked about putting a resistor between the case and the 0.
But that's a no go.
Icsaszar makes a good point though that if the power wire touches the casing , not only a shock but will destroy my computer.
The way I build , it is not exactly a Class II appliance ...
If the case of the computer is not earthed, you might feel a tickle when touching it. It can sit at half mains voltage, but it is not dangerous. This is because the mains input X capacitors that normally shunt HF noise to the PE, form a voltage divider between line-case-neutral when the case is not connected to the PE. Definitely not good for audio 