ZP80 ground loop issue and solutions

Been a while but my ZP hum issues were solved by changing the polarity of all my connected equipments plugs one at a time, if it still hums but at a lower level after a change, conti je the process after noting the component.

Once all have  been tried either the problem isn't the polarity or there are two problem components. Go back and try changing just the noisy ones and see if it helps.

Hum transformers aren't horrible if you get the right ones for your connection and good quality.

Optical out on the ZP to the new kit would be best.

Cheers, I’ve done some of that but scratching the surface, it wasn’t making it better the hum is still there. Tried changing every cable connected, on wifi, different mains ring and physical separation. I’m veering towards buying up some ZP100s. Plenty on ebay for <£50. Don’t need the amp but from what I can see the standby current is only 3W more than the ZP80. Don’t like the bulk and weight but these will be secreted in a service cupboard and nobody will see them.

Disappointed because I really thought the earthing would work. Unless, of course, there’s a better earth point inside the ZP80 - I haven’t opened up to look or guess - maybe the plate you see through the underside is for shielding and not electrical ground?

ZP80’s often introduce hum. My suggestion is inserting isolation transformers in the signal path. If you dig around there will be offers of very cheap “ground loop eliminators”. These are just capacitors that will reduce bass somewhat and not be completely effective at eliminating the hum. Ground isolation transformers are lifelines for pros that manage large systems in studios.

If there is a cable box in the system, sometimes disconnecting the coax to the street will reduce or eliminate the hum. Regardless, make sure that the coax shield is properly connected to your house electrical ground. In addition to reducing or eliminating the hum this is also for personal safety and reduced risk of lightning damage.

Plenty of opened up ZP pictures out there, never looked at mine.

Only reliable cure I found was getting the mains polarity swapped around to make everything happy.

I’m semi concerned about the whole ‘secreted in a service cupboard’ comment. My previous (and old) experience with ZP80s suggested they ran warm, and needed a lot of air cooling. Secreted away wasn’t what I expected to be good for them. 

No coax in the system. Why I’m asking about the in-line transformers as I know they will do ‘a job’ as opposed to the cheapo 60Hz high pass filter types but are the transformers any good or is there still frequency or dynamic loss? Prices vary from £25 to £100s so to be cheaper than simply replacing the ZP80s with ZP100s it will have to be the low end and I’m nervous to buy and find I made the wrong choice versus the certainty that a ZP100 will fix my problem.

Otherwise my ZP80s have been in a service cupboard for 20years and are still going strong! As are my ZP100s. There’s always adequate airflow. 

It never helped my case but I’m interested what the science is behind why ‘swapping the polarity’ might work for some?

At least in the US, one side of the power connection ls somewhat referenced to ground, possibly at the transformer out on the pole, but it carries current. Therefore this “ground” potential varies with current draw due to voltage drop in the wiring. Meanwhile, the ground lug on the outlet shouldn’t be carrying much current and should be attached to a ground rod driven into the local soil as power enters the house. There is almost always a small potential difference between the two “grounds”. This difference will likely be different at each outlet and vary with the load. Many power plugs are keyed such that the connected equipment knows which power wire is closer to “ground”. Plus, the audio equipment “ground” might be hard connected to the outlet’s building ground terminal.

In order to reduce RF interference in both directions the audio device’s internal chassis ground is tied to a power conductor “ground” with a capacitor. But, unless the power plug is keyed, it’s 50/50 you are using the best connection for the “ground”. It’s a big mess. This “ground” reference usually finds its way to the shield connection in the audio system. As you interconnect the audio devices, their shields are connected. If there is a potential difference between the shield connections there will be current flow in the audio coax shield. The resulting current generated magnetic field induces hum into the signal wire that should have been protected from external interference by the shield. And, there can be issues internal to either component because each unit assumes that its shield connection is at “zero”. In a gaggle of components using un-keyed power plugs, there may be an arrangement of plug orientations that will reduce hum, but there is no guarantee.

The use of isolation transformers eliminates this audio mess.

The ZP80 is unusually susceptible to ground loops.

Only suggestion for isolators is to read reviews and specs.

An additional issue with US power is we have two power legs with 240 volts between them and a neutral that is 120 volts from either power leg. Plus in some newer homes there is a ground connector. Having 120 volt appliances using one power leg and the neutral leg can induce a bit of noise in it.

Also if your gear is using both hot legs there is the possibility of 240 volt induced hum, out of phase though so it is either much worse or self canceling depending on the specific situation.

Newer electrical equipment has polarized connectors, hoping to minimize issues, and preventing the plug flipping, not always effective though.

Jensen transformers has a wide variety of isolators used by many pros.

Cheers, retailers indicating the jensen home theatre isolators are discontinued! Nonetheless, prices $130-270? I saw a pre-owned audiophile range one on ebay for >£300! Reviewers indicating no discernible sound degradation. That might be the way I need to go in future as those Cyrus amps do seem more prone.

I’m still thinking buy a couple of ZP100s off ebay instead? I’m hoping they outlast me. Realistically, Sonos S1 does all I need  but will likely fall over at some point. With any similar replacement it is going to have the same issues of double insulation and likely USB power so I’ll think about it for a couple of days. I could still jump on a WiiM just for the sheer hilarity of trying it. However, I think it is a significant consumer issue going forward.