Nait 5 ground loop hum buzz … thing

doctordjbrown

Please forgive YET ANOTHER posting about ground-loops. This forum seems to be both the most friendly and have the most sensible postings, and is therefore the place to lay my head in shame … I can't work it out. What is going on? Any help gratefully received.

1) I have a Nait 5 plugged into a 13A double socket.

2) I attach my BW360s and turn it on. Beautiful silence. No hum. However high the volume. Not even a hiss.

3) I attach a good quality 5-pin DIN plug, terminating in a 3.5mm jack to the CD input and place my finger over the end of the jack. Unsurprisingly I get a bit of a ground-loop hum. I AM the ground loop and the source. The buzz gets worse the higher I turn the volume.

4) I put the jack into a little Bluetooth device that I bought in the USA (Amazon.com: Auvio Bluetooth Music Receiver: Electronics - which is powered through a little 12V two-lead (live/neutral, no earth) little transformer. This is connected to the mains socket right next to the Nait. NO BUZZ. Brilliant, beautiful music through bluetooth. Nice. I can listen to anything my iPad can deliver. This is now the ONLY way I can listen to anything on the amp because if ...

5) I remove the jack from the bluetooth thingy and replace this source with pretty much any piece of, albeit fairly low-end, equipment (my internet TV, an apple Aiport Express … and so-on) ALL of which have only TWO leads (live/neutral, no earth) … then the amp buzzes like a wasp on heat … OK, i know wasps don't have oestrus but you get the idea. A LOUD 50Hz buzz - which is loud even when the volume is turned to ZERO and doesn't vary when you turn the volume. This is louder than the buzz I get by touching my finger to the end of the jack.​
This problem has been going on since I moved to the country a couple of years ago - I had no such problems in the city (no idea if this is relevant, but I should mention it).

Things I have tried:

1) Taking the Amp to a NAIM dealer, who plugged it in, played a bit of cello music and declared it in perfect working order

2) De-Earthing the Nait (just briefly you understand, as a test)

3) Exchanging Live and Neutral in the Nait's mains lead (hey, it was worth a try)

4) Changing every lead, piece of equipment and connector (the Nait and the speakers remain)

5) Moving HOUSE (for other reasons, of course, but in case you asked).

6) Adding a ground-loop isolator into the mix (although it was only a cheap one).

6) Surfing, googling and generally trawling every site on the internet for suggested solutions - finding this very helpful: Minimising Hum - and this too: Naim nait 5i and sonos zp90 humming problems | AVForums
​I suspect that this is about having a non-balanced input … I can't understand how it works with the little bluetooth device and then so differently with other equipment.

Any insights gratefully received.

Thanks again for reading this far.

Mark.Yudkin

Could you repeat the experiment using the "internet TV, apple Aiport Express … and so-on", but with absolutely nothing plugged into the internet TV, Aiport Express, etc. Then repeat with only the power cord connected to the internet TV, Aiport Express, etc and plugged into the same wall socket as the Nait. What happens in these two signal-free (and therefore useless) cases wrt hum?

doctordjbrown

Mark. Sorry for the delay in replying.  Thank you again for taking the time to help me with this ...

I tried doing what you suggested with the airport express, as follows:

Nait: ON
Speakers: plugged-in
Nothing else attached to amplifier (Blissful silence)
Attach 3.5mm - 5-pinDIN cable to Nait (No hum)
Unplug Airport express
Attach 3.5mm jack to Airport Express (No hum)
Plug Airport Express into (switched-off) wall socket next to amp (No hum)
Turn Airport Express on at the wall ... big-ol Humdinger of a HUM.

So … to answer your question, the AE only causes the hum when it's in the wall AND it's receiving power.

PS: Since posting my original question, I've ordered this: ART DTI Dual Transformer & Ground Loop Isolator at Juno Records

DJ

Mark.Yudkin

Weird. The Airport Express is not grounded through the power and there is no connection other than the NAIT. Moreover you said you'd tried "De-Earthing the Nait (just briefly you understand, as a test)". I just don't see how this can be a ground loop hum. Please post back when you've tried out the ART DTI transformer.

doctordjbrown

Hello again - and thanks for taking the time with this. It's not entirely clear what's going on - although the hum is exactly the right frequency (it has that characteristic 50Hz feel to it).

I've tried the DTI transformer and … no improvement at all. No change in symptoms whatsoever.

What is more bizarre is that if I have now discovered that when the bluetooth adapter connected is to the amp input, but NOT plugged into mains, all is fine until I switch-on the Airport Express at the mains (but NOT connect it to the amp) - at that point I now get the hum, not as loud as if directly connected - but still very audible. If I move the bluetooth leads away from the AE then it decreases.

To clarify, simply switching-on the AE at the wall is enough to induce a hum in the lead, even though the AE is not connected to the amp.

Which brings me to a point where I wonder if I have a problem of NO EARTH connection, rather than a loop. In Naim nait 5i and sonos zp90 humming problems | AVForums, which I have just re-read, Gumboot says:

Have I simply got a FLOATING earth? If so, what's the safest and most efficient way of testing this theory?

Thanks again for any input!

DJ

noiseboy72

You can try taking an earth cable between an unused input socket earth and a mains earth and see if it helps.

Now, is it a hum (100Hz) or a buzz (50Hz)? This is important, as hum loops generally create 50Hz, while power supply faults - like faulty capacitors create hums  - due to partial rectification through the input bridge rectifier and are usually quite low level.

doctordjbrown

Oooh. Excellent question - I hadn't considered the difference between a buzz and a hum. Having listened more carefully I think it's both. There is a very low buzz AND a hum, which is likely twice the frequency since I hadn't recognised it previously as a harmonic. I recorded the noise (I'm glad no one was watching me) but sadly wan't permitted to upload an MP3.

Once again, thank you for joining in my pre-christmas puzzle. I will find a way to earth one of the inputs and let you know. I'm not sure what the rest of the household are going to think if I attach one of the amp's audio inputs to a wall socket … and I suspect that Maplin are unlikely to stock a lead with a 5-pin DIN on one end and a 13A plug on the other …

noiseboy72

Try a length of thin wire, plugged into the earth pin on the din, run under the case to the earthing point...

Might be a bit neater than a 13A - Din (Although I do have a 13A to BNC, for earthing video D/As on the end of long Cat5 runs!!!)

Mark.Yudkin

I think we can safely conclude that you do not have a ground loop. Also a buzz is not a hum at 50Hz (60Hz in US sources), by definition buzz in audio "consists of a mixture of high-order harmonics of 50/60Hz" - Noisbeoy is confusing his noises... Anyway take a look at http://www.jensen-transformers.com/an/an004.pdf, although I rather think it doesn't describe your problem.

As a first stab, can you take the Apple Express into the shop for testing / replacement - I'm tipping a faulty power supply?

doctordjbrown

It may seem an age since I posted my frustrations just before Christmas. And it is. The clocks go forward today. Spring is sprung and ... life is sweet and, most thankfully, blissfully free of both buzz and hum.

For those that have a Nait-5, it may be worth noting that the inputs are not earthed. Attaching unearthed equipment simply leaves the input dangling, ready to pick-up every passing eddy current and induction voltage that may be in the air.

Taking a length of wire from the chassis to the middle pin of an unused DIN socket silenced the nonsense. I have, for the last couple of months, been enjoying my music once again.

Thanks to NoiseBoy, Mark.Yudin and especially to GUMBOOT (in the other thread) for your help and support. Sorry for the delay in confirming this was solved.

DJ