How dangerous is lifting the ground on a source component?

[tmtomh]

My current signal chain is not ideal but for now it's what I have: source component (Oppo UDP-205) into graphic EQ, into power amp (Purifi-based unit). I have recently been hearing some low-level hum through the speakers when I go near them and no music is playing. (And no, I have no idea why the hum has appeared or else increased in level recently.)

I am using unbalanced interconnects because the EQ unit does not have balanced inputs or outputs. I have reasons for having the EQ in the chain, and while I am not permanently attached to this setup, I'd rather not get into that right now - I understand that moving to balanced interconnects could solve this problem in the long term.

But here is my question: After unplugging things, switching things around in different receptacles, swapping AC cords, power strips etc, and fiddling with lights and dimmers around the house, I have narrowed down the source of the hum to the Oppo in the following way:

• Amp turned on, other components off, RCA cables disconnected from the amp = no more hum. So it's not coming from the power amp. It must be one of the two upstream components.
• Amp on, other components off, RCA cables connected from amp to EQ, but disconnected from Oppo to EQ = no more hum. So it's not the EQ (or at least it's not the EQ interacting with the amp).
• Amp on, other components off, RCA cables connected to all components, but Oppo power cord unplugged from wall = no more hum. As soon as I plug the Oppo back in, the hum returns.
• And finally, amp on, other components off, RCA cables all connected, Oppo plugged into AC BUT the Oppo's ground lifted (via a heavy-duty extension cord with a three-prong receptacle for the Oppo's cord but only a two-prong plug going into the wall socket) = no more hum. The setup is literally just as quiet with the ground lifted as it is if I unplug the Oppo from AC entirely.

So while I freely admit I do not fully understand how hum can be caused through the interactions among components, this process of elimination seems to show that when I lift the ground of the Oppo, the problem goes away.

For this reason, I have a Hum-X on order. Even though it does not lift ground (and therefore is safer), it apparently achieves the same result if the problem is a ground loop (and not EMI, for example). Only time will tell of course - I'll have to try it out and see.

In the meantime, I am wondering if it is actually unsafe to operate the Oppo with a lifted ground. I would not even consider, even as a temporary measure, lifting the ground on a power amplifier. But I am wondering about lifting the ground on a 2V line-level source component (which I am using for audio only - there is no TV hooked up to it or even in the room). Is it just as dangerous because we're still talking about mains power going through the unit's internal transformers? I would definitely want to prioritize safety, and it's a simple matter to wait a few days for the Hum-X to arrive and then try it. I'm just curious about the real-world implications of using a source component with a lifted ground.

Thanks for any advice or guidance folks can provide - and again, I understand that moving to a setup with balanced interconnects would likely be a better long-term solution here.

 

[JSmith]

Is it just as dangerous because we're still talking about mains power going through the unit's internal transformers?

I would suggest so yes... my thoughts are never lift ground in any electrical product. It's just unsafe in general and may even be illegal in some parts.



JSmith

 

[wwenze]

Lifting the ground on *anything* has the same danger. Don't care whether it is a power amp or a DAC with a tiny transformer, because it is the primary side voltage that kills you, not the secondary side.

 

[tmtomh]

Thank you for your super-quick replies. That's what I thought. Much appreciated!

And in the hopes of establishing that I'm not a complete idiot, I'd like to clarify that I only tried the ground-lifting arrangement for a few moments and never turned on or even touched the Oppo while it was plugged in that way.

 

[brimble]

I have a related question. I've recently bought a second-hand TEAC A-H500i amplifier, which hasn't arrived yet, and I'm very surprised to see this in the owner's manual:

Could this amplifier really not be earthed?

 

[sergeauckland]

I have a related question. I've recently bought a second-hand TEAC A-H500i amplifier, which hasn't arrived yet, and I'm very surprised to see this in the owner's manual:

View attachment 166308

Could this amplifier really not be earthed?

Yes, if it's double insulated. It should have the appropriate symbol on the back, of two squares, one inside the other.

S

 

[solderdude]

I have a related question. I've recently bought a second-hand TEAC A-H500i amplifier, which hasn't arrived yet, and I'm very surprised to see this in the owner's manual:

View attachment 166308

Could this amplifier really not be earthed?

Manual says it is not. And yes, the rear shows the double insulated sign.
However, the enclosure is metal and for double insulated the demand is there should be no metal parts that you can touch.

The metal enclosure can be grounded via a screw but that is intended for Phono inputs.

A possibility is that the mains cable goes directly into the transformer in a way that ensures mains voltages cannot come into contact with the metal enclosure. In this case it is important that the metal enclosure is NOT making contact with the common (audio ground) either otherwise the metal enclosure can still have a voltage on it coming from connected gear.

 

[escksu]

ITs perfectly fine to run equipment without ground and not all equipment have ground (some are 2pin only).

However, if yours has one, I do not recommend lifting it, esp. if the casing is metal. The whole idea of grounding is to provide a low resistance path for the power to flow so you will not be electrocuted. If any mishap happens and you are touching the equipment, you risk being electrocuted. It can kill and the victim may not be you.

There are gears that can resolve your ground loop issue (both commercial and DIY) and I recommend them instead of lifting the ground.

 

[escksu]

I have a related question. I've recently bought a second-hand TEAC A-H500i amplifier, which hasn't arrived yet, and I'm very surprised to see this in the owner's manual:

View attachment 166308

Could this amplifier really not be earthed?

Not all amps have earth wire. ITs relatively common for amps to have just 2 pin. IF you livei n Europe, type C would be among the most common. IF in US, type A.

Plug & socket types

www.worldstandards.eu

 

[Doodski]

it is important that the metal enclosure is NOT making contact with the common (audio ground) either otherwise the metal enclosure can still have a voltage on it coming from connected gear.

If there is a ground issue it is possible the devices can source ground from each other through the connections other than the power connections? I have seen this often when high current DC powered devices are connected and one has a bad or poor ground. The unit with the bad ground sources the ground from other components through the RCA or other connections and then the PCB traces are melted and go open and the system ceases to operate.

 

[rkbates]

Sort of like buying a Lamborghini - if you need to ask the price you can't afford it. It you need to ask the question, you shouldn't be disconnecting earths.

 

[escksu]

IF you are keen to DIY, you can make one of these. They are also available commercially.

Project files: Little helpers – Ground Loop Breaker

One more little helper for you guys :) Once again, not exactly a major effort with this one, but I hope it is still useful. What is it? It’s a Ground Loop Breaker as described in this article by Ro…

theslowdiyer.wordpress.com

Using a bridge rectifier to break ground loops

Using a bridge rectifier to break ground loops

www.diystompboxes.com

 

[Blumlein 88]

Them that suffered the worst from a lifted ground ain't around to say are they?

 

[sergeauckland]

If you are genuinely suffering from a hum loop, and a lot of so-called hum or ground or earth loops are nothing of the sort, then by far the best way is to use a double-wound audio transformer in the audio cabling between the item causing the hum and the rest of the system. A pair of good quality transformers will cost something around £100, but they will work properly, and not affect sound quality. There are cheap ones available, and they may work well enough, and will prove the point that it's really a hum loop before spending on a good quality unit if the audio quality of the cheap one is inadequate.

I've used mine to get me out of trouble several times.

S

 

[solderdude]

If there is a ground issue it is possible the devices can source ground from each other through the connections other than the power connections? I have seen this often when high current DC powered devices are connected and one has a bad or poor ground. The unit with the bad ground sources the ground from other components through the RCA or other connections and then the PCB traces are melted and go open and the system ceases to operate.

Yes, that crossed my mind and wrote it (but deleted it from the draft). For that the enclosure must be connected to the audio ground inside the amp.
In that case the manufacturer would have to rely on safety ground reaching the amp via RCA connections. That would be an irresponsible thing to do. What if none of the connected devices would have safety ground connected to audio ground ?

 

[JSmith]

Them that suffered the worst from a lifted ground ain't around to say are they?

Indeed...

Leslie Harvey - Wikipedia

en.wikipedia.org

Harvey was a co-founder of Stone the Crows in late 1969. It was while on stage with Stone the Crows at Swansea Top Rank in 1972, that he was electrocuted after touching a microphone that was not earthed while the fingers of his other hand were holding the strings of his guitar. It has been incorrectly stated that the incident happened "on a rainy day with puddles on the stage"; however, Swansea Top Rank was an indoor venue and therefore this was not possible. A roadie attempted to unplug the guitar, but was unsuccessful. Harvey died from his injuries, aged 27.

Further, ground lifts do not conform to Audio Engineering Society standard AES48;

https://www.aes.org/tmpFiles/aessc/20211118/aes48-2019-i.pdf

JSmith

 

[Doodski]

For that the enclosure must be connected to the audio ground inside the amp.
In that case the manufacturer would have to rely on safety ground reaching the amp via RCA connections. That would be an irresponsible thing to do.

I have used the chassis as a ground reference on many amps/receivers etc. It worked great as a reference; the chassis was common to the RCAs and other ground planes in the devices. I have experienced amps that when connected to speakers hum loud without a RCA connected and then when connecting another component through the RCA the hum stopped. So they sourced a ground through the RCA.

What if none of the connected devices would have safety ground connected to audio ground ?

Then the issue should not occur.

 

[solderdude]

This is more of a safety ground issue (from my P.O.V.) not so much if it works in practice.
In practice it will work fine.
Only in the very unlikely event that in said power amp a full short exists between 'live' and the metal enclosure and one would have to rely on safety ground to be connected via other connected gear using RCA shields and the safety ground pin of one of the other connected devices it could be dangerous. Chances might be very, very slim if that were taken into consideration designing the amp.

In general, for mains fed devices that have metal parts one can touch these parts should be connected to safety ground.

Ground lift, depending on how this is technically done, depends on multiple (well more than 1) devices being connected and being grounded through the connected devices.

Ground lift may be dangerous in certain (fault) situations but can be beneficial in certain practical implementations in the field.
Ground lift switches should be used with knowledge of what it does. Sadly... in general the knowledge is not there.

 

[wwenze]

Lots of audio amplifiers and AVRs have metal chassis yet are considered double-insulated or use the C18 connector btw. Maybe even the one you're using right now.

It is completely feasible. Proof of concept: Throw an extension strip into a computer chassis. AC voltage, in a metal chassis. Yet completely safe.

As an interesting yet related note, some computer chassis like NR200 that has the PSU mounted in the front of the chassis will use a normal-looking AC cable to run from the back of the chassis to the front where it terminates with a C13 connector. Same concept, made use of some technicalities, but as a result still completely safe. (Do not under any circumstance use DIY-ed cables for this, I have seen some people do that.)



Secondary ground is generally not dangerous to touch or expose. (Ignoring the fact that they can and often do float to mains voltage / 2, but that topic is for another day.) In the first place, what is the "absolute voltage" of secondary ground to begin with? Zero? Not really. It's irrelevant, since it is behind an isolation transformer. Connecting secondary ground to such a chassis is therefore generally safe, because both are by themselves safe. But do not under any scenario connect a secondary side ground to a chassis that is connected to mains earth, as that modification actually has the potential to kill you.

 

[brimble]

Not all amps have earth wire. ITs relatively common for amps to have just 2 pin. IF you livei n Europe, type C would be among the most common. IF in US, type A.

Plug & socket types

www.worldstandards.eu

Great. Thank you! I think it might be illegal here in Australia, but if it's safe then I won't worry.