So it looks like there is a 50Hz hum which goes away when nothing is connected to the amp, but the strong 100Hz remains, and raises the others (150Hz, 200Hz, 250Hz, 350Hz etc).
I have ruled out a faulty amp as I have had issues with the following amps as well (Cambridge Audio A5, Nuforce STA120, Parasound Z-Amp and a MiniDSP 2x4HD). The only amp it does not show up as much on is my Decware Zen SET.
All these amps I have shown the same issues so I belive that its down to ‘dirty’ mains, the Decware does not show it up as I’ve been told as its very low gain (2wpc) with the very sensitive speakers it will not show the noise as much?
They are all being powered through the Wychwood mains conditioner.
They do indeed go between the source and the amp. But at this level they’re not very special. The primary market is for in-car systems which TBH aren’t hi-fi. You may well find that you lose bass with these and that more subtle colouring can go on further up the frequency spectrum. More annoyingly the internal magnetics, such as they are, aren’t well shielded so the damn things can, if they’re placed too close to other equipment, pick up hash and hum from the mains transformers ! I have one and I use it for fault diagnosis i.e. giving me info about where the problem arises. But I wouldn’t use one as the solution.
Somewhat better are branded pro-audio products e.g. those from OEP or the basic Neutrik stuff.
i) that the odd harmonics - 50Hz, 150Hz, 250Hz etc vary with the connectedness or otherwise of the inputs. This is what you would expect of ground loop noise, which almost always contains 50Hz plus odd harmonics, although it can have some even harmonic contributions too.
ii) that the even harmonics (100Hz, 200Hz, 300Hz …) don’t depend on whether anything’s connected to the inputs. This indicates either amp noise or noise from some completely external source. 100Hz is characteristic of rectified mains i.e. what you get from power supplies. Biggish amps have biggish power supplies. Rega don’t seem to specify how much hum should come from the Elicit. I’ve looked around for a review of it which includes some hum measurements but I couldn’t find one. Of course actually getting off one’s bum and measuring stuff went out of fashion years ago (pace Stereophile and also Paul Miller in HiFi News) and instead reviews now consist largely of telling you how taut and/or etched and/or blancmange-like the sound from the amp is. Fuck me .
So let’s do some rough sums. I find that with bog standard, say 89dB/Wm 8ohm speakers, hum at about 1.4mV RMS is just audible and at 2.8mV RMS is distinctly audible (100Hz is more audible than 50Hz and higher harmonics can make it a good deal more audible still). 2.8mV is 60dB below 1 watt output, so 80db below 100 watts, which your amp is. Your speakers are 10dB more sensitive than bog standard ones, so if the hum was 90dB below 100W it would still be audible.
Back in the day 90dB down would have been regarded as very decent performance from an amp. But what about now ? The nearest I can come to judging it is with Stereophile’s review of the Rega Brio - a 50W/ch integrated. The nitty gritty is in the paragraph just above fig 3 here https://www.stereophile.com/content/rega-research-brio-integrated-amplifier-measurements. Restricting the measurement bandwidth to the audio range (22Hz-22kHz) they measured overall noise at about 70dB below 1W, which would be 90dB below 100W (I know the amp can’t do 100W, but that’s just an arbitrary reference level, so it doesn’t matter). If all the noise was 100Hz hum then with your speakers I reckon you’d be able to hear it. But, at least with the Brio, maybe it isn’t all 100Hz hum ? Fig 3 should tell us. What it shows is that in fact there is a good deal of mains frequency related noise (the fundamental is at 60Hz in the US, of course). It’s not the whole story, but it’s clearly there (further complicated by the fact that I think that Fig 3 has been A-weighted, which artificially suppresses the low frequency peaks, in which case they would be bigger in real life than in the pic - by 16-17db at 120Hz and 27db at 60Hz).
Long story short - it’s possible that the Elicit just does hum a bit. If you want to stop by with it next time you’re passing I’ll get the HP3561A down and we can measure it. It (the measurement) would take about 5 minutes.