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Yet another weird ground loop issue, and I thought I had left these stupid things behind

suttondesign

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So my bedside setup had been a Mac mini, topping dx3, and a little topping headphone amp, all running unbalanced. but I started getting a low-level hum that disappeared if I touched a case or unplugged the Mac mini. I ruled out the USB connection. The Mac mini was a 2012.

In the course of troubleshooting, the old Mac mini got much worse! Really loud buzzing. So I threw that shit away and got a new, dinky Mac mini. Pretty cool.

Low-level hum persists. So I pull out a Topping DX7 combo DAC/amp that had been mothballed owing intermittent weird screeching in the signal. No more hum. Since it's defective, I'm using it until my new Topping DX5 combo unit arrives. No idea what to do with the DX7 -- obviously I can't sell it to anyone.

Over the years, I've had these problems crop up, and I usually just ditch a setup and replace stuff until things work again. But I suppose the DX5 will break in a year or two, and I'll be back to square one. Sigh.
 
Barely know these components, but does the Mac mini connect to the Topping via USB?
 
I've had mains leakage go from my PC through USB to the DAC, then up the earphone cable, exciting the driver in the process, and finally returning through my body into earth somewhere.

Shit was bizarre.

If I took off my socks the mains hum would get worse.

If my feet touched the brick wall instead of my wood floor, it would get worse still.

If my hand touched the DAC's metal housing, the hum would disappear, likely because the leakage current now took the shorter path through my arm instead of following the earphone cable and reaching the driver.

What fixed it for me was the addition of a USB isolator.

Would recommend looking into those yourself if mains leakage is something that you struggle with, and using Optical is not an option.

If using Optical is an option, I'd recommend you do that.

You can add Optical out to your Mac via a Hifime UT23 or Cubilux SPDIF Converter.
 
So my bedside setup had been a Mac mini, topping dx3, and a little topping headphone amp, all running unbalanced. but I started getting a low-level hum that disappeared if I touched a case or unplugged the Mac mini. I ruled out the USB connection. The Mac mini was a 2012.

In the course of troubleshooting, the old Mac mini got much worse! Really loud buzzing. So I threw that shit away and got a new, dinky Mac mini. Pretty cool.

Low-level hum persists. So I pull out a Topping DX7 combo DAC/amp that had been mothballed owing intermittent weird screeching in the signal. No more hum. Since it's defective, I'm using it until my new Topping DX5 combo unit arrives. No idea what to do with the DX7 -- obviously I can't sell it to anyone.

Over the years, I've had these problems crop up, and I usually just ditch a setup and replace stuff until things work again. But I suppose the DX5 will break in a year or two, and I'll be back to square one. Sigh.
Since the hum disappears when you touch the case it suggests there is no actual earth connection in the system at all. The small leakage current is then grounding through you. Most likely you can get rid of the hum by connecting a ground wire to an unused RCA somewhere, and connecting the other end to the earth connection of a mains socket. If you try this make 100% sure you connect to ground, and not live or neutral. The latter two would almost certainly end very badly. :D
 
Since the hum disappears when you touch the case it suggests there is no actual earth connection in the system at all. The small leakage current is then grounding through you. Most likely you can get rid of the hum by connecting a ground wire to an unused RCA somewhere, and connecting the other end to the earth connection of a mains socket. If you try this make 100% sure you connect to ground, and not live or neutral. The latter two would almost certainly end very badly. :D
Oh, that's interesting. Do you mean literally a plain piece of solid copper 12-gauge from an rca jack to the third prong of a plug I get at a hardware store and then plug into an outlet?
 
I've had mains leakage go from my PC through USB to the DAC, then up the earphone cable, exciting the driver in the process, and finally returning through my body into earth somewhere.

Shit was bizarre.

If I took off my socks the mains hum would get worse.

If my feet touched the brick wall instead of my wood floor, it would get worse still.

If my hand touched the DAC's metal housing, the hum would disappear, likely because the leakage current now took the shorter path through my arm instead of following the earphone cable and reaching the driver.

What fixed it for me was the addition of a USB isolator.

Would recommend looking into those yourself if mains leakage is something that you struggle with, and using Optical is not an option.

If using Optical is an option, I'd recommend you do that.

You can add Optical out to your Mac via a Hifime UT23 or Cubilux SPDIF Converter.
I tried the optical connection, and that didn't solve it. I did consider the USB isolator, but it was a less certain path since my problem persisted even with optical. My new Mac mini does not have an optical connector, but I want to look at those options you just mentioned.
 
You can try switching the sampling rate and then switching back.
 
Do you mean literally a plain piece of solid copper 12-gauge from an rca jack to the third prong of a plug I get at a hardware store and then plug into an outlet?
12 gauge seems way oversized even. Something akin to a typical turntable ground wire ought to do just fine.
 
check your electrical system, starting with the plug or power strip if the earth ground is wel connected. In worst case your the grounding of the electric system in your house does not work like intended (I had that in a rental house long ago), but the chance is bigger that it's a broken power strip or wall plug, where the ground connection is broken. It happens more than people think, and in most cases you won't notice it untill there is a big problem. With audio systems you hear it as the ground hum comes into your signal because it does not find another way out.
 
Oh, that's interesting. Do you mean literally a plain piece of solid copper 12-gauge from an rca jack to the third prong of a plug I get at a hardware store and then plug into an outlet?

Pretty much - but from the ring of the RCA (Not pin). 12 gauge not needed. See here for my implementation
 
Pretty much - but from the ring of the RCA (Not pin). 12 gauge not needed. See here for my implementation

It occurs to me that it would be fairly easy to add a 10mm grounded stud or even 4mm banana socket to the front of a UK mains faceplate and avoid the need to waste a mains socket. If the pattress is metal and has been correctly grounded, then you could probably ground off one of the screws holding the faceplate on (perhaps screwing straight through the centre of a 10mm stud). I'm guessing that Part P might have something to say about this and wouldn't approve.

*edit* Ha! I knew i'd find some audiowoowoo if I looked long enough... £264!

 
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then you could probably ground off one of the screws holding the faceplate on
Even with plastic faceplates (metal ones in the home are not common) the screw normally goes into an earthed metal back box. (Where the socket is in a brick/plaster wall - Plasterboard (Dry) walls will often have plastic back boxes)

Ha! I knew i'd find some audiowoowoo if I looked long enough
Yep - an absolutely bog standard double socket with a hole drilled through the faceplate and a banana plug plus some screen printing added. Nice little earner if you can sell any.
 
Even with plastic faceplates (metal ones in the home are not common) the screw normally goes into an earthed metal back box. (Where the socket is in a brick/plaster wall - Plasterboard (Dry) walls will often have plastic back boxes)

I said 'metal pattress'. Pattresses can be surface mounted or recessed. Recessed ones are also known as 'back boxes' :)

In any case, I think the screw holes in the faceplate have to be earthed these days, so it wouldn't matter if the back box was plastic as long as the screw still made good contact with the metal part of the hole.

I might have a go at making a faceplate, sockets are in short supply in my study, there are only 2 doubles and they all have multiway adapters or a UPS (with multiple outputs) plugged into them.

I see that it's common to include a 1meg Ohm resistor in-line for ESD protection equipment to ensure low current flow through earth should something become accidentally live. Since i'll be using the bonding point primarily for this purpose, I think I should include a resistor as well.


Yep - an absolutely bog standard double socket with a hole drilled through the faceplate and a banana plug plus some screen printing added. Nice little earner if you can sell any.

I'd have to fake the Rhodium plating with a silver pen :)
 
My thoughts on all this:
a] the needed ground/earth connection is to the Safety Ground/Protective Earth system, not Planet Earth.
b] in US, if you have 3 pin wall receptacles, check them (all you can find) with a little 3 LED tester.
c] many 2 pin computers, dump power supply noise onto their metal chassis. Then the noise travels thru your interconnects back to the Safety Ground/Protective Earth. Making what is often called 'ground loop' noise.
d] it is a good idea to have all the exposed metal chassis's at the same potential.
e] first do one or more components have a 3 pin connection to a good 3 pin wall outlet? (will get back to this later)
f] plug all the components into the same outlet strip/distribution box.
g] you can dumper any 2 pin components to a connected 3 pin component with a 12 to 16 AWG wire.
at needed to be attached to bare metal (remove paint or anodizing)
attaching near the input or output connectors is best.
or you can attach it to the shell/ring of a chassis mounted RCA connector, but not a RCA connector with a plastic insulator ring.
h] don't do any of this to a all plastic case component, the has a double insulated 'square within a square' safety symbol.
 
check your electrical system, starting with the plug or power strip if the earth ground is wel connected. In worst case your the grounding of the electric system in your house does not work like intended (I had that in a rental house long ago), but the chance is bigger that it's a broken power strip or wall plug, where the ground connection is broken. It happens more than people think, and in most cases you won't notice it untill there is a big problem. With audio systems you hear it as the ground hum comes into your signal because it does not find another way out.
it’s a new house, so this could very well be the issue. i will pull the outlet and check. the house has a huge new ground rod.
 
The ground rod has little to to with the situation.
* * * * * * * * * * * * * *
the Neutral and Safety Ground/Protective Earth do have continuity to Planet Earth, but that's about it.
 
So my bedside setup had been a Mac mini, topping dx3, and a little topping headphone amp, all running unbalanced. but I started getting a low-level hum that disappeared if I touched a case or unplugged the Mac mini. I ruled out the USB connection. The Mac mini was a 2012.

In the course of troubleshooting, the old Mac mini got much worse! Really loud buzzing. So I threw that shit away and got a new, dinky Mac mini. Pretty cool.

Low-level hum persists. So I pull out a Topping DX7 combo DAC/amp that had been mothballed owing intermittent weird screeching in the signal. No more hum. Since it's defective, I'm using it until my new Topping DX5 combo unit arrives. No idea what to do with the DX7 -- obviously I can't sell it to anyone.

Over the years, I've had these problems crop up, and I usually just ditch a setup and replace stuff until things work again. But I suppose the DX5 will break in a year or two, and I'll be back to square one. Sigh.
Up to and including 2014 Mac Minis, you can also connect your devices via the optical port.
If the problem still persists, a USB isolator is unlikely to help.
You could unplug all other devices and lamps in the room and check whether the humming is still there.
 
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