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SHD - Ground Loop Hum 7 months 3 weeks ago #52360

  • daermonn
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Hi folks,

Just received my SHD, very excited to replace my old DAC + preamp (Schiit Gungnir + Parasound P3) with something more functional.

Unfortunately, I plugged it in and am now getting what sounds like a fairly loud ground loop hum when I turn on the power amp (Conrad Johnson MF200). Turning the volume up or down on the SHD does not affect how loud the ground loop hum is.

Right now my system is connected like: laptop (unplugged) --usb--> SHD --rca--> MF200 -> speakers.

The connections between old components are still there, but neither the power amp nor the SHD are connected in any way, and everything besides the SHD and MF200 are unplugged from the wall and should be totally out of circuit.

Any idea what could be causing this? I tried fiddling around with what I could think of but nothing changed it. I've run into glh problems before, but nothing in a long time. Pretty bummed, was looking forward to getting started with the Dirac tuning.

Thanks!

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Last edit: by daermonn.

SHD - Ground Loop Hum 7 months 3 weeks ago #52367

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If the power plugs in your country are symmetric (like in germany) it sometimes helps to turn them around in the socket..

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SHD - Ground Loop Hum 7 months 3 weeks ago #52370

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Thanks! In the US, so all asymmetrical 3 prong plugs.

After listening to it again for a while, I'm not convinced it's actually a ground loop... I've always had a slight buzz/hum out of my left tweeter due to amp noise floor/caps starting to go; it sounds like the same buzz is now coming out of the right tweeter as well.

It wasn't doing this - only the left tweeter - prior to swapping in the SHD, so not sure why this would trigger it.

So yeah, it might just be my amp going bad... Might try using a ground lift plug to see if that helps, if it doesn't seem dangerous.

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SHD - Ground Loop Hum 7 months 3 weeks ago #52374

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Okay -- it's definitely a ground hum issue! I lifted the amp plug with a 3-prong to 2-prong cheater and the buzz went away -- system is MUCH quieter, and the SHD sound fantastic. So not an issue with the amp like I suspected it might be.

Any idea why the SHD is causing this grounding issue where my old preamp/DAC setup wasn't? I believe the previous preamp was ungrounded, but it looks like the SHD is...

What's the best way to solve this grounding issue? I have reluctantly used a cheater to lift the amp before, but I don't really like it for safety reasons. I will eventually be getting a pair of NC400 monoblocks with balanced connections, which should help -- but is there a best solution in the interim? Would it be better to lift the SHD instead of the amp?

Thanks!

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SHD - Ground Loop Hum 7 months 3 weeks ago #52382

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Changing where you plug in the two components can make a difference. As you say, I wouldn't remove the earth connection from either piece of equipment for safety reasons. Also, in the very unlikely event that a subsequent fault then lead to a house fire you'd probably find you had invalidated your insurance too.

Does your power amp have any different (lower) gain settings, or or do you happen to have any inline attenuators? I'm not sure, but I think it's possible that either could help by improving the SNR.

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SHD - Ground Loop Hum 7 months 2 weeks ago #52471

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Nope, my amp doesn't have any gain, nor do I have inline attenuators. Everything is plugged into the same Belkin power supply unit, underneath my audio stand. Is it worth trying to switch one component to a different circuit or something?

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SHD - Ground Loop Hum 7 months 2 weeks ago #52477

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Ground loop hum is caused by low frequency electromagnetic radiation being received by the loop area.
There are 3 ways to solve it.
1. Minimise the radiation, if there is no radiation for the loop to receive there will be no hum. If possible turn off every other powered device nearby and see if the hum stops. Turn things back on one by one and hopefully find the tramsitter. If the hum never stops your amplifier is possibly the transmitter.
2. Minimise the loop area. This is typically achieved by having the two devices connected to the same circuit with their mains cables running together to the two devices close together. A very short signal connection between the devices should then result in a minimal loop area.
3. Break the loop. This is easy with a balanced signal connection but not possible with an unbalanced signal connection. In the latter case assuming the signal ground and device earth are one and the same it is possible to lift the earth on one device but this has safety implications. Lifting is not the same as removing and the safe way to lift an earth is to introduce sufficient impedance to attenuate loop hum whilst still providing a sufficiently low impedance earth for a safety current path. I do not encourage anybody to do this unless they understand the theory and risks and I will not provide any further advice on that, IT CAN BE DANGEROUS if not done properly. Consult an expert if you need to go that route, introducing balanced connections is far easier and safer.

The good news is that low frequency electromagnetic radiation doesn't travel far, that's why radios use hugely higher frequencies. The bad news is that methods 1 and 2 can help but often don't completely solve the problem. Method 3 is the only complete solution which is why balanced connections are typical in harsh environments.

I have a fully unbalanced system here with a hifi, 3 mixers and a large number of synths connected to a stupidly large number of sockets albeit all on the same electrical circuit. I don't get any hum despite having multiple ground loops over huge areas, presumably because there is no significant low frequency electromagnetic radiation into these loops. I'm lucky.

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Last edit: by entripy.

SHD - Ground Loop Hum 7 months 2 weeks ago #52486

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Yes, as far as ground loops go, luck has a lot to do with it.

TV's have been problematic for me. So in my main listening area, I will never have a TV. In my TV room, I finally solved a ground loop problem by getting one of these:
www.ebay.com/itm/361990052321

This is a very useful link for understanding ground loops, much of which has already been summarized by @entripy:
www.jensen-transformers.com/?s=ground+loop

Jensen products are not inexpensive, but they work, are backed by well researched science and are very well made.

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Last edit: by rodrigaj.

SHD - Ground Loop Hum 7 months 1 week ago #52611

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Is the SHD and amp plugged into the same outlet?

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SHD - Ground Loop Hum 7 months 1 week ago #52640

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I had exactly the same situation and my TV is forming the loop with SHD, but not with my other devices..
I am currently floating the TV ground pin.
Wonder whether SHD has design issue or just pure unlucky

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SHD - Ground Loop Hum 7 months 1 week ago #52642

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No design issue, ground loops are common so you're just unlucky to hear hum.

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SHD - Ground Loop Hum 7 months 6 days ago #52716

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I just managed to solve my ground loop issue - not sure if your situation is similar, but posting in case it helps.

Just got my SHD today, hooked everything up, turned the system on, and... aaaaaack! What is that terrible whistling sound coming through my speakers when nothing is playing?!? Volume up and down made no difference.

Turned out it's my amp's fault.

I have a McIntosh MC-152. I had my Sonos Connect feeding it through the RCA input. I had my SHD feeding it through the balanced input. The amp has a little switch to select which input to use so I had it set on balanced... you can probably see where this is going...

It appears that my amps design didn't completely isolate the 2 inputs, so while I thought I had disengaged the RCA input, I had actually created a ground loop.

Solution - unplugged the RCA cables... all fixed! No more ground loop.

As a side note, MiniDSP needs to hurry up with the official Roon cert. Because it's unsupported, I can't use by SHD with Roon, so now my Sonos is feeding the SHD with Roon through toslink... not exactly what I was hoping to use the SHD for (wanted to use the onboard streamer), but at least the SHD DAC seems to *decimate* the Sonos DAC. Next up is to pit the SHD Dirac 3 against my home made convolution filter...

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Last edit: by eisenb11.

SHD - Ground Loop Hum 4 months 1 week ago #54681

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The SHD may not have the best noise filters implemented. My receiver and SHD were both connected to the same subwoofer via RCA which resulted in a ground loop hum only coming through the SHD - even when the receiver was off (standby). No issues when the SHD was in standby and the receiver was playing. So the receiver was doing a much better job at rejecting the same noise.

After spending many fruitless hours messing with replugging components into different outlets and cheater plugs, I finally got a “Ground Loop Isolator (GLI-200)” from Amazon, and connected it between the SHD and the subwoofer. Problem Solved!

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SHD - Ground Loop Hum 4 months 1 week ago #54702

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Firstly, there is no such thing as a filter for ground loop hum, so whether the SHD or some other item has better or worse impossible filters makes no sense. No device can reject ground loop hum. It can lift the reference away from ground or avoid using ground as a reference with a balanced system but it can't reject noise on any formed loop.

Secondly, I would actually draw completely the opposite conclusion to yourself. Since the issue went away when the SHD was in standby it suggests the SHD may be being as helpful as it can be by disconnecting the signal reference from ground in standby. When the receiver is in standby it doesn't bother doing anything so the hum continues.

However, I am pleased you managed to isolate your loop to solve your problem. Ground loops are often difficult to reason about because they loop through multiple devices.

Its also always worth remembering that the issue depends on three separate factors. It requires electromagnetic radiation into the loop area of a ground loop. A ground loop alone does not cause hum. I have over 70 ground loops in this room and have no hum. If the loop area is small it massively reduces hum. I have six 8 way unbalanced looms bound together and running near the mains supply to minimise the loop area for all 70+ loops. Additionally I am in roofspace far away from any significant electromagnetic radiation.

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SHD - Ground Loop Hum 4 months 1 week ago #54705

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I think you misunderstood my comments and were quick to jump to conclusions, so let me clarify.

In my setup, the SHD and Processor (I’ll call it AVR) are connected to separate inputs on the subwoofer. They are also connected to the power amp through an RCA switch.
The AVR never had any hum (from the speakers), regardless of the SHD existence or powered on state. However, the SHD introduced significant hum/noise into the speakers when the AVR was simply connected to the subwoofer (I did not test with the AVR unplugged from mains)

My conclusion was that the processor was able to filter the noise and prevent it from entering the speaker outputs (either through isolation or active filtering), while the SHD couldn’t.

See this link where Amir discusses noise filtering circuits in audio equipment. Although he is referring to mains noise - so slightly different.
audiosciencereview.com/forum/index.php?t...audio-devices.21057/

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