@TheSnafu and others.
I'm located in Finland, and bought a 230v Freya (and a Vidar) from the Dutch importer, schiit-europe.com. It took quite a while for first Freya to come into stock in early summer, and I waited for the Vidar for a couple of months more. Other related gear is listed in my profile, but the speakers are 91dB Tannoy XT 8F's. (I was wondering about getting two Vidars.., but read on.)
Basically I bought the unit for my first foray into tubes, and to get into tube rolling, but I've been trying to tackle a noise problem. I've got a ~50hz (transformer/tube?) hum which doesn't change with the volume control/mute relay on.
The passive mode and JFET's are completely silent, although with your ear directly by the speakers' driver, you can hear the noise floor rise with JFET even so slightly. With tubes, the noise floor rises quite audibly, but the hiss isn't heard from the listening position - the hum is.
The thing is, all the tubes I've acquired (dozens of pairs from various vendors), including the stock tubes has this issue, and all of them with varying degrees of the before mentioned hum. Some (matched) pairs are almost undetectable (but they are producing the hum - when you switch the modes you do notice, especially in a corner of the room where the frequency is naturally amplified), and some are quite vehemently producing this hum.
This hum is continuous 50hz hum, (I did a tone generator test). It isn't buzz, it isn't random tube artifacts appearing and disappearing, it isn't crackle, and it's not hiss. The hum doesn't change with touching Freya's chassis, holding it tighter to the surface it's resting on (tested various surfaces and places), nor does it change if I lift/tap the chassis or tubes (microphonic tubes convey clanks, thuds and thumps etc. to the speakers), and no weight above Freya's chassis help with the hum either. I've tested various electric sockets, and various ground combinations. I've even tested various socket savers. This has led to a conclusion that tube dampeners won't help with my issue.
I lent an isolation transformer for this weekend, only connecting the Freya into Vidar (with RCA to work in stereo mode) and obviously the speakers with cables, if I could tackle the problem but to no avail. I tested the isolation transformer in between the units and before them, with different ground combinations. No help. (Perhaps I could bring down the hum a slight notch when grounding the extension cord after the isolation transformer as the grid after the transformer isn't grounded.)
I can produce a ground loop with Freya (touching the chassis raises the same hum), as I can lift the ground easily. (Take note
@Koobre , if that's your only problem, you're in luck I guess?)
The only thing still to test is which I can think of is a Jensen isolator (
@cskippy mentioned Radial Engineerings DI-box) in between Freya and Vidar? Any other suggestions?
I haven't reached Sonority or Schiit yet; and it's a miracle I've found time to even do some minor testing in the past couple of days. On a sick leave due a flu, but otherwise the year has had to offer a death in the family, water damage in our normal flat (we've been living in another flat during the renovation since Midsummer, just got the OK this week to move back), 1- and 3-year olds running around in the house and SO starting to study again. I feel a bit overwhelmed. The 14 -day return periods have long since gone, but I guess warranty is still an option.
TL;DR is this even tube hum, does it exist, and if so, should I hear it with my speakers?
Could either Freyas or Vidars transformers be the source of problems, where either the isolator, or even a line attenuator might help?
