Earth Loop Hum

555CD/552/300

I have a hum on all inputs which my dealer informs me is due to an earth problem.  Unplugging the interconnect between the 555CD and 552 resolves the problem but means I can't play music obviously .  To be fair, my dealer has tried really hard to fix it but without joy.  So far we have tried the following:

Different interconnects (several!)

Running a long extension cable from different electrical sockets.

An electrician with HiFi experience checking the supply.

Substituting the CD player (including PS).

Substituting the preamp (including PS).

Yet another interconnect, this time with earthing crocodile clips at the source end.

Really frustrating.  My dealer is going to escalate as high as possible at Naim but thought I'd raise in case anybody has helpful thoughts.

 

Bryce

Original Post

PCD makes a very good point. The other thing i'm not clear about is whether the 300 has been substituted during the investigation - if it hasn't then i have a couple of easy things you can try yourself that may help you track down the issue. 

From what you describe i'm wondering if you have an unintentional second signal ground to chassis ground occurring due to a wiring fault somewhere. If you disconnect all the components from the mains and each other, use a DVM on its continuity setting and do the following.

With the CD555 connected to its 555PS and not plugged into the mains. Measure between mains plug Earth and the outer ring on one of the signal output RCA's - you should have continuity as this is where signal ground and mains ground is connected in a Naim system.

With the 552 connected to its 552PS and not plugged into the mains, measure between mains plug earth and one of the RCA input connectors outer rings - there should be no continuity. 

With the 300 connected to its 300PS and not plugged into the mains, measure between mains plug earth and the -ve socket on one of the XLR inputs - there should be no continuity. 

Remember when doing these checks, apart from the Burndy cables connecting the PS units to the head units, do not have any other interconnects between the 555 / 552 / 300 head units. 

James

 

 

 

Several diagnostic questions:

  1. Do you plug any auxiliary components into your system? If yes - this is the most likely culprit.

  2. Are are you plugging all the NAIMs into one, earthed mains? Different mains rings / circuits may have different voltage (minute differences) which will in turn manifest themselves as hum.

  3. Are all mains cables properly earthed?

  4. Does the system hum when it's on but no sources are connected? As I understand the system hums when CD555 is connected so this question will narrow down where the problem occurs. If the answer is NO, than the culprit is CD555 and it's wiring.

 

Correct me if I'm wrong, but do the CD555 and the NAC552 not require power supplies?

If so then you haven't fully described your system.

That suggests that there may also be other components connected that you also haven't mentioned.

If you haven't described your system accurately, how do you expect us to attempt diagnosis or throw any useful light on the situation?

Huge posted:

Correct me if I'm wrong, but do the CD555 and the NAC552 not require power supplies?

If so then you haven't fully described your system.

That suggests that there may also be other components connected that you also haven't mentioned.

If you haven't described your system accurately, how do you expect us to attempt diagnosis or throw any useful light on the situation?

Bryce mentions substitution of the PS for both 555 and 552 in his original post and i'm assuming it's just those 3 components (including PS's) mentioned....

Thank you gentleman, much appreciated.

James N - have not tried substituting the 300.  And what's a DVM?  I'm guessing a voltage meter?

Adam:

1.  Rega TT and Arcam 850 (I use my loudspeakers as Front L and R channels in my home cinema setup.  The Arcam passes through those two channels to the Naim system).

2.  The Naim equipment is all into one earthed mains.  The Arcam is on a different circuit but we did the experiment using a long extension cable of putting it on the same circuit and the problem persisted.

3.  They're Chord Sarum Super Aray power leads so for the money I've paid they should be properly earthed which isn't the same as saying they are of course.

4.  The hum goes the minute the CD555 and 552 are disconnected.  When connected the hum is present on CD and AV input.  I don't think it is on Phono input.

Huge - sorry, 555PS and 552PS.  Both have been swapped to see if the hum is eliminated without success.

Most likely the Arcam is also earthing the signal 0V creating an earth loop with the CD555/555PS.

The signal earthing in the Arcam needs to be set to floating.

They should most definitely NOT be connected to different earth circuits.

Bryce Curdy posted:

 

Adam:

1.  Rega TT and Arcam 850 (I use my loudspeakers as Front L and R channels in my home cinema setup.  The Arcam passes through those two channels to the Naim system).

2.  The Naim equipment is all into one earthed mains.  The Arcam is on a different circuit but we did the experiment using a long extension cable of putting it on the same circuit and the problem persisted.

 

Bingo - that's why I've asked question no 1

A very common problem and I'm surprised your dealer did not pick up on that (mind you - mine did not spot it either in my setup - Yamaha Aventage 5000 into 252).

As Huge wrote you have a perfect ground loop for several reasons: Arcam is not earthed (the 3rd pin on the mains is not connected); you are powering your Naim and Arcam from different mains circuits.
Even if they were on the same circuit, you'd still most likely get an earth loop.

Solution:
An isolating transformer (stereo version) costing a princely sum of GBP 10 or so connected between your Arcam output and your NAC 552 input. It will break the galvanic connection between the Arcam and NAC but will maintain the signal's purity. Search for 'stereo islation transformer'.  
This should cure the problem.

Adam

 

Very common problem.  I added a CD5X to my AV-connected Naim system and got the hum -- so I blamed the CD5X for my issue.  

Per my dealer's recommendation, I tried disconnecting CATV at the point it enters my home, which eliminated the hum, as predicted.  Solution was to add the isolater between my Denon amp and Naim preamp, just as Adam suggests.

Nick

Very grateful but don't want to get my hopes up.  In terms of confirming the above unplugging the interconnects from the Arcam 850 from the 552 should eliminate the hum when on CD source?  I thought we had done that but I've lost track.  And assuming it does just add the isolation transformer.

Bryce - the thing with an earthing issue like this is to start with a simple configuration - ie just 555CD as source and then add the other sources back in to see when the hum comes back. It sounds likely to be the Arcam so if it is then add the isolation transformer as Adam suggested. 

First step - 555/252/300 only nothing else (TT, Arcam) connected. Any hum ?

Unplugging everything with the exception of the CD555 makes the problem dramatically worse.  The hum with the volume at 8 o'clock is now the same as it was with the volume dial at full.

The TT is connected to a StageLine.

i have Sky Q Silver, Oppo 203 UHD, Amazon Fire TV and Apple TV connected to the Arcam.  It outputs to a 7.1.4 Atmos system with the Front L and R passed through to the 552.

The Cinema Room was made by knocking two bedrooms together.  The Hi-Fi equipment is in one 'room' together with the Sub and TV.  The Home Cinema stuff is in the other.

Each 'room' has a Control4 network controller with IR blasters for the stuff that cannot be operated via home network.

Hmm - if you still have hum with only the 555 connected to the 552 then it looks like we can discount the AV system and TT causing the problem and just concentrate on the 3 components (555/552/300) and their power supplies. 

Did the dealer use the same Burndy cables each time or try different ones ?

As the 300 is the only thing that has not been substituted for another component i'd recommend substituting that with another Naim amp to be sure it's not the problem here. 

One more thing Bryce - when did the hum start ? I take it this has not always happened so what did you change when the hum problem started ?

James

Bryce Curdy posted:

Unplugging everything with the exception of the CD555 makes the problem dramatically worse.  The hum with the volume at 8 o'clock is now the same as it was with the volume dial at full.

The TT is connected to a StageLine.

i have Sky Q Silver, Oppo 203 UHD, Amazon Fire TV and Apple TV connected to the Arcam.  It outputs to a 7.1.4 Atmos system with the Front L and R passed through to the 552.

The Cinema Room was made by knocking two bedrooms together.  The Hi-Fi equipment is in one 'room' together with the Sub and TV.  The Home Cinema stuff is in the other.

Each 'room' has a Control4 network controller with IR blasters for the stuff that cannot be operated via home network.

Something does not add up - sorry, but what you wrote is completely counterintuitive...

Let's establish some basic facts:

Case 1: CD555 + NAC 552 + NAP 300 (and their power supplies) = horrible hum

Case 2: CD555 + NAC 552 + NAP 300 + Arcam connected to NAC 552 = less hum, but still annoying

Did I understand your reply correctly?

I've been accused at least once of not telling everything.  I forgot to mention that the Arcam 850 connects to a 4 channel Arcam power amp to feed the Atmos channels and that I have a Lumagen Radiance Pro between the four video inputs and the Arcam 850.

James N:

Not sure about burndy, need to check.

Agree about 300.

Your last question has a slightly complicated answer.  I noticed the problem after I moved house at the end of last year at which time the AV input on the 552 was changed to a balanced one.  Previously for AV I set the volume on the 552 to 9 o'clock and for CD and phono would only ever go up to about 10 o'clock.  Now the hum on the balanced AV input is obvious and if I experiment and turn the volume up higher on the CD input it becomes obvious but is absent/minimal at my usual 9 o'clock volume level and is absent at any volume on the phono input.  Hope that makes sense but I may have had the problem but not realised it for years.

Adam, you understood me perfectly.  Counterintuitive is an understatement but that's what's happening.

 

 

Bryce - i'm not sure what the balanced conversion on the AV input involved - was this a modification done by Naim or is it just a custom made cable ?

Again you say the hum is there when no other source components are connected to the 552 so this rules out the AV setup creating an earth loop. 

From what you describe regarding the hum, it sounds like it's more background in nature (rather than a loud buzz. How do you have your components arranged (i.e. power supplies kept away from the head units) ?

James

Bryce

Naim does NOT have balanced connections. 
Your Arcam does not have balanced outputs either.

But... that's not the problem 

This statement is a problem:

Previously for AV I set the volume on the 552 to 9 o'clock and for CD and phono would only ever go up to about 10 o'clock.

With an AV Bypas set correctly there is no way you can control the volume on your NAC 552. It's impossible by design.
The volume control duties are assigned to your ARCAM in this setup. Front Left and Front Right go directly (via NAC 552) to your NAP.

Bryce - can you photograph the back of your Arcam?
I need to see the connection you have used to feed the signal from Arcam to your NAC.
Also please post a photo of your input on NAP where it's connected.
Have you enabled the AV Bypass feature on your DIN input 4 or 5?

Adam

 

I've probably not explained myself properly.  At my old home if I was watching an AV source I would set the 552 volume at 9 o'clock.  If I wanted to increase the volume on all channels of what was then a 5.1 system I would increase the volume on my AV processor, and if I wanted to adjust the volume on front L and R channels independently I could use the 552 volume control.   Now for AV the volume setting on the 552 is preset (no light on volume control)  and I can only adjust the volume for all channels using the Arcam AV processor.

Adam - I think you misunderstood or more likely I did not explain things well.  I didn't have an AV bypass in my old house which meant the hum could have been there all along but I never noticed because it wasn't obvious on AV input at 9 o'clock and I never turned the volume up high enough on any input.

Bryce Curdy posted:

Adam - probably/possibly - but surely if I still have hum (more hum) with AV disconnected then I have another problem entirely unrelated and exclusive to my Naim boxes???

Adam makes a valid point that the AV system could still cause problems (when it is connected) and the simple solution to this is adding the isolation transformer. This is a separate problem which doesn't explain why you still have a hum problem when you only have your 555/552/300 running with nothing else connected. 

So...

Get those Burndy cables checked

Get your dealer to substitute another Naim amp in place of the 300 

Refer your dealer to post 4 which may help him. 

Any chance of posting a picture of your setup - I'd just like to see the placement of the items in relation to each other and anything else you may have in your rack. 

James

 

Bryce Curdy posted:

Adam - probably/possibly - but surely if I still have hum (more hum) with AV disconnected then I have another problem entirely unrelated and exclusive to my Naim boxes???

If there is still hum with nothing whatsoever connected to the 552 other than the CD player, then the issue has to be with the Naim boxes. That needs to be resolved first. Then add the AV amp and if there is a new hum that then needs to be fixed. 

I've been away for the holiday weekend and have my dealer coming out again later.  Fingers crossed.

If he's not successful I'd been asked to attach photos.  I can see the Insert/edit image icon above but no idea what I'm supposed to do next.  What do I put in as Source?

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