Hi all this is my first post so please be gentle. Apologies in advance for any etiquette misdemeanours. I come to electronics through an interest in audio. I’ve been at it for a few years and am perhaps not a beginner but I am inexperienced and an amateur.
I want to better understand the use and safety considerations of DIY isolated / floating class 1 PSU’s, particularly in respect of audio. To be clear a conductive chassis that houses mains leads (active and neutral) are always directly bonded mechanically and electrically to PE. This question relates only to referencing the 0V rail of on the isolated side of a trx to PE.
I’ve been reading and learning about grounding topologies for DIY class 1 linear PSU’s, the circuits they power as used in audio (i.e amps, active xovers, DAC’s etc) and the associated noise that can result. It has become clear that the majority of advice found on forums and websites is that a DIY class 1 isolated / floating PSU’s should not be used i.e. the 0v rail should always be referenced to Protective Earth (PE). A reason is that of safety: should a trx fault occur where mains voltage passes across to the secondary side, the user has a greater chance of protection because fault currents could flow to PE and might trip a protection device.
Examples of this:
1. Audio Component Grounding and Interconnection by Dave Davenport on diyaudio -
https://www.diyaudio.com/archive/articles/186018-what-gain-structure-next-thread.html2. Ground Loops -
https://hifisonix.com/ground-loops/3. Grounding - https:
//www.valvewizard.co.uk/Grounding.pdfAnother reason given in forum threads is that the use of isolated, floating supplies is problematic for reasons other than safety. Unfortunately these “other (technical?) reasons” are not elaborated upon.
However, there are a small number of people who say that isolated, floating PSU’s are perfectly safe in the audio context and even preferred from a safety perspective. One such person was an old electronics engineer I had a conversation with many years ago who took the position (as I understood it) that once mains voltage had been isolated, it should be left floating / isolated unless there was a reason against this. His reasoning was that an isolated, floating PSU provided a smaller surface area from which electric shock could be obtained, i.e. a risk only existed between 0v rail and the +/-. He argued that referencing to PE increased the surface area that an electric shock could come from, i.e. a person touching the +/- rail and any PE connected (conductive) surface could be shocked. His view was that it could not be relied upon that RCD’s would always be present (an example might be an older home that still relied on CB or fuses). Unfortunately we did not discuss the topic of trx failure and mains appearing on the previously isolated side.
Knowing that lab bench PSU’s (DIY and otherwise) are usually class 1 isolated / floating devices and don’t seem to generate passionate safety arguments I am left confused as to why a floating/isolated PSU in the audio context would be unsafe or be problematic for technical reasons.
Having now come to understand the arguments for always referencing DIY class 1 audio PSU’s to PE and following the grounding topologies in the links shown above to avoid noise, I wish to more fully understand the arguments for why. Vague references to safety and even vaguer references to “other reasons” doesn’t help form a complete understanding of the topic. My goal here is to understand the topic from all sides, enhancing my overall electronics knowledge.
My questions are:
1) What are the safety concerns in using a floating / isolated class 1 PSU and can they be overcome?
2) What are the non-safety “technical reasons” that would make using isolated / floating PSU’s problematic in an audio context?
3) Are those that are using isolated / floating PSU’s in audio exposing themselves and others to unacceptable safety risks as the weight of opinion as per the links above would suggest?
Many thanks to all.