Ground loop issues...

Are your stuff all wired to the same power outlet?
If not try that, even your computer (or another source), as ground (by shield wire) is usually carried over to dac.
An insufficient PE (ground wire in mains) conductance can produce hum from pickup of nearby line(s), in this case it's better to get rid of it.

 

I only have two power outlets in my room. One for the TV on one end & the other one at the far end for my PC.
I have a surge protector strip for both of those outlets that I connect my all PC & TV stuff.

I been listening to my audio gear today with the TV/surge protector unplugged from one of the wall outlets. I guess that's not a bad comprise.

 

What are the connections you have in the system? From components to outlets and among the components. It helps to draw all this out so you can identify the 'loop'. Note that it's not surprising an isolation transformer doesn't get rid of a ground loop: that's because both sides are connected to the same ground (see e.g. the schematic here).

 

An isolation transformer will usually fix common mode noise problems - a voltage delta between neutral and ground, which can cause these symptoms. Laser printers, for example, are good at creating common mode voltage. I haven't seen a definitive determination of a ground loop here. So, yeah, he needs to draw this out. Which connected components could be forming a loop? Disconnect one at a time, and go from there.

 

I thought that getting rid of ground loops was just a case of connecting everything to the same socket. Then I googled, and ended up with this horrible hum in my head.

I used to earth all my hifi equipment to the gas pipe (London houses had stuff like that). Without doing so, there was always a tingly feeling on the cases and, if the turntable was in use, a big buzz from the speakers. I don't know if using a gas pipe as an earth is "good practice," but, hey, London is still there.

 

@Thad E Ginathom

Pure gas is actually non-flammable, it's only when you mix it with oxygen (or some other suitable gas) that you can get a reaction. So not as dangerous as you might think. Same thing with pure oxygen really. Fire is the chemical reaction of two or more materials interacting at a molecular level, so if you're only heating one single kind of molecules nothing much will happen. Well - of course if you heat a solid you can make it turn into liquid and then a gas, but if you're heating a pure gas nothing much will happen except that it will get hotter and in a confined space the pressure will rise. If you heat it enough eventually you'll get plasma, but that's not a task for your kitchen stove.

 

Yes an isolation transformer fixes some issues but as far as I understand, it doesn't break the 'loop' since both primary and secondary have their grounds connected.

As a side note: I need a step down transformer for my amp and using an isolation step down transformer as opposed to the usual autoformer essentially eliminated mechanical hum in my amp's power transformer... but that's a different issue (noise or DC offset on the actual line).

 

There's isolation on the AC, and there are the little isolation boxes for the RCA cable connection... The former will help with common mode voltage, the latter - manufacturers claim - will break the loop. I'm not so familiar with the latter, but here's a reasonable (?) write up. I might be tempted to try that Iso-Max box, if I had root caused the issue down to a particular connection.

 

I encountered a really bad ground hum when I connected an integrated amp via RCA to the pre-outs of my AV receiver. I tried re-arraning and plugging/unplugging everything to try and get rid of it but to no avail.

In the end I tried the Ebtech 2 channel Hum eliminator between the two amps and It worked like a charm. Not exactly cheap (£60) but oh, sweet silence.

I'd love to be able to diagnose the problem properly but I didn't know what else to try. In any case, apart from cleaning up the hum it doesn't seem to affect the sound quality in any other way I can tell. The box is set up for 1/4" jacks so I just needed TS adaptors for my RCA cables.

Prior to that I tried two other cheaper isolation boxes and 1 worked to a lesser extent and the other actually made it worse.

 

If you've already confirmed that the system has no noise with just the amp and DAC plugged into the wall, it seems to me that what you might be hearing is noise from the power supplies in the TV and/or computer when they are plugged in. Have you confirmed which of those two devices is causing the noise? When you used a device with an isolation transformer, was everything plugged into it or just the audio stuff? Are you using shielded RCA cables from DAC to amp?

 

are you using a usb dac by chance? unplug the usb cable from your dac and see if the noise goes away. The ground coming from computers can be terribly noisy and can be transferred over the usb ground on the cable to your dac and introduce a lot of noise

(had this issue first hand)

 

The TV is plugged into one socket & the PC into another, when plugging my audio stuff in either sockets, I get the same noise.
I also only plugged the audio stuff into the isolation transformer. In hindsight, I should have tried plugging different combinations into the transformer, but since it didn't
initially work, I sold it off.

The way the noise comes & goes is very strange. At one time, I plugged my equipment in, there was no noise, but when I switched headphones into the amplifier, the noise immediately came back & wouldn't go away.
Sometimes the noise is a loud buzzing sound that is only heard at higher volumes & other times the noise is a low audible crumpling sound that is independent of whatever the volume knob is at.