Simple question about earthing power supplies for audio circuits. - Page 1
Forum section: electronics / beginners

author: tiltit
author_rank: Regular Contributor
timestamp: December 04, 2016, 03:26:42 pm
content: Hi, I am currently building a linear power supply for a desktop cmoy headphone amp I would like to build.I understand that if the case for my project is metallic it must be earthed, but I am not sure if I should earth GND as well.Should I do that, or can there be any unforeseen problems like a audible ground loop with that?Thanks.

author: Simon
author_rank: Unknown
timestamp: December 04, 2016, 03:48:39 pm
content: It should not make much difference either way.

author: tiltit
author_rank: Regular Contributor
timestamp: December 04, 2016, 03:51:36 pm
content: Ok, thanks.I can get on with the layout now.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2016, 04:16:23 pm
content: Actually it can cause major problems with hum on line level signals. The easy answer is to 'float' the input socket grounds, apart from a resistor of about 100K to discharge static to ground (and isolate them from the case) then use either a differential amplifier (+ ESD clamping diodes to the rails), or a coupling transformer to provide a ground referenced signal to the rest of the circuit. That also makes it easy to support balanced line inputs.

author: tiltit
author_rank: Regular Contributor
timestamp: December 04, 2016, 04:56:34 pm
content: QuoteNow this is getting more complicated. For now I will leave the power supply ground disconnected from from earth.I will deal with the amp later. here is the schematic.https://tangentsoft.net/audio/cmoy/misc/cmoy-tangent-sch.pdfI am really not used to dealing with mains on a pcb.I've attached the schematics and layout of my power supply. Can anyone let me know if it is safe or not?It will be home etched. Probably tonight.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2016, 05:05:09 pm
content: Because its a headphone amp, its *NOT* safe unless the transformer has an earthed inter-winding shield, or is a split bobbin type with at least 5KV isolation between primary and secondary or the secondary is earthed, or you transformer isolate the headphone socket.

author: snarkysparky
author_rank: Frequent Contributor
timestamp: December 04, 2016, 05:12:24 pm
content: land the power line ground onto the case for safety. Isolate the input grounds from the case. Dat'z my vote

author: tiltit
author_rank: Regular Contributor
timestamp: December 04, 2016, 05:25:41 pm
content: I knew it! whatever I do is wrong.This is The transformer I am using.http://cdn-reichelt.de/documents/datenblatt/C500/RKPT%23TAL.pdfUnfortunately the document is in German and mine isn't all that great. But I figured out: Class A insulation at 105 degrees Celsius. They also mention in the applications note, professional audio appliances. And the transformer is potted.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2016, 05:55:02 pm
content: There's a considerable difference between what's acceptable for a general purpose pro or consumer AV item and one that has a headphone socket. Many headphones do NOT have reinforced insulation, and they are used in continuous skin contact with the head so the risk of electrocution is much much higher, especially as their insulation may be compromised by sweat. In addition to the need for adequate reinforced insulation, you should follow the two faults principle - the output should remain safe if any single component fails. Grounding the secondary side also provides protection against faults in the signal source.