Best way to prevent loud buzzing noise in case signal ground is accidently lifted from power amp input (RCA)

[PHD]

Hi

A few years back, I almost killed my Focal Aria when I stepped on the RCA cable connecting my Denon pre-out to my Hypex Ncore power amp.

Because the Denon uses a 2-prong AC while the Hypex amp uses a 3-prong AC, and the interconnects are single-ended, the only galvanic signal ground path is through the RCA cables. So if the RCA connector becomes loose, the signal ground is lifted, generating a loud buzzing noise from the speakers.

The way I see it, there are two possible ways to avoid this issue:

1. Add a grounding post (like one found next to phono inputs) to the Power amp and connect a grounding wire between the Amp chassis and the AVR's chassis using the phono grounding post. This creates an alternative signal ground path which is secured by the grounding posts' screws on both ends. However, this requires modification to the power amps which voids its warranty.

2. Connect a grounding wire from the AC main' earth prong to the AVR's phono grounding posts. Because the power amp is already grounded to search using the included 3-prong power cord, this will also create an alternative signal ground path in case the RCA becomes loose.

Of course, one of the above methods could potentially cause ground loop hum.


The third option, which isn't applicable, is to switch to XLR balanced connection, but these are not supported by the AVR.


Which option do you think is best and safest?


Thanks.

 

[Ruhled]

Route your wires where you can't step on them? These all seem like much worse choices.

 

[wwenze]

Have a pair of RCA cables so that when the ground disconnects from one the other still has it?

 

[PHD]

Have a pair of RCA cables so that when the ground disconnects from one the other still has it?

I only have one RCA input on the power amp. What is the problem with running a separate ground wire from the AVR to the power amp or grounding the AVR using an additional ac cord?

 

[wwenze]

I only have one RCA input on the power amp. What is the problem with running a separate ground wire from the AVR to the power amp or grounding the AVR using an additional ac cord?

Primarily because we don't know how and where the grounds are wired without further testing

- connect a grounding wire between the Amp chassis and the AVR's chassis
In majority of devices the chassis is not connected to the secondary ground. In class 1 equipment the chassis is likely (but not guaranteed) to be connected to mains earth, and in class 2 many chassis are left floating. Connecting such a chassis to secondary earth will break safety regulations.

- Connect a grounding wire from the AC main' earth prong to the AVR's phono grounding posts. Because the power amp is already grounded to search earth using the included 3-prong power cord, this will also create an alternative signal ground path in case the RCA becomes loose.
Power amp is connected to mains earth somewhere. Not necessarily at the secondary ground side and unlikely to be directly connected. (Connection via a capacitor + resistor is more likely)
The phono grounding post is likely to connect to secondary side somewhere, likely (but not guaranteed) secondary ground.

Anyway testing is free, just do whatever that works, there's no right or wrong except when it comes to safety and insurance.

 

[Hayabusa]

Add a paralel input resistor to lower the input impedance of your amp

 

[restorer-john]

So the OP pulled out an RCA cable while the amplifier/s were plugged in and switched on and "nearly" killed his attached speakers.

Nearly? They made a great big buzz and they still work right? And that was a few years ago and they still are working? What's the problem? Unless the OP is incredibly clumsy and trips over/pulls out RCA cables regularly- this is just not an issue.

Turn off your gear whenever you're messing around behind it and route the cables sensibly. Don't mess around with earthing double insulated gear either.

 

[somebodyelse]

I guess this sort of situation is why Neutrik made RCAs that ensure ground makes contact first and breaks contact last.
https://www.neutrik.com/en/neutrik/products/phono-rca-connectors/profi-cable-connectors

 

[PHD]

So the OP pulled out an RCA cable while the amplifier/s were plugged in and switched on and "nearly" killed his attached speakers.

Nearly? They made a great big buzz and they still work right? And that was a few years ago and they still are working? What's the problem? Unless the OP is incredibly clumsy and trips over/pulls out RCA cables regularly- this is just not an issue.

Turn off your gear whenever you're messing around behind it and route the cables sensibly. Don't mess around with earthing double insulated gear either.

This happened to me twice. Once with the Hypex amp which was my fault to accidentally step on the RCA cable with one hand. The other time it happened spontaneously but with my SVS subwoofer. This turn out to be a bad "high quality" subwoofer cable made by SVS.. It just randomly lifted the ground causing loud hum. Yes, in both cases no damage was done but this could have easily happened the the middle of the night waking the entire house. So I feel more comfortable knowing it cannot happen.

And I did a test. Connected the earth pin from the outlet to the Denon chassis. Now I get galvanic continuity between the the signal ground of both the Denon AVR and Hypex power amp even w/o the RCA connection. So the Hypex chassis is physically connected to the signal ground. I guess grounding the AVR is the simplest way to achieve this.

I even made a special AC cord for this purpose. The AVR's ground is now earthed and also connected to the Turntable ground lead. I do not hear any hum and the amp works fine.