Thank you everyone for the input!
We worked pretty hard to try ensure that the loud hum (100-120hz) and a bit of high frequency fizz was coming from the power and wasn't a source issue. This is for a pretty low-fi active studio monitor system that is taking signal directly from an SMSL M8 DAC with linear power supply. The house power is completely atrocious, but for now (and with no tubes in the mix yet) we have gotten it to a livable level
Turns out the Presonus 5" active monitors have a case of bad case of gain-itis - the line level from the SMSL DAC was hot enough that using the default gain (it is a rotary adjustment on the monitor) it was amplifying some signal noise (the fizz) and the ~100hz noise from the power supply, and the local country music station. By dropping the gain setting on the monitors to nearly off - when you back the dial all the way back it goes from low to off - and using a much higher source setting (at the digital level) we were able to improve the signal to noise ratio. Combining this with a Pyle 10 outlet, 2U sequential power /voltage stabilizer/ line filter that we had on hand seems to be enough.
Still a bit of hum when there is no music playing out of one channel (the amp is not the best quality for sure in those, but for under $200/per what do you want?) and he is a happy camper.
What does this mean? Was this thread for naught? NO!
Once we build the tube setup, we are going to have to address the power quality issues. I'm thinking medical grade outlets on a dedicated circuit, home brew IS Trans, center tapped for balanced power as an option, with something like a PS unit for outlet control and additional filtering ahead of the BeePree (on order) , DAC and SS amp. Once we have a better handle on the power draw for the system, expect me to be back kneeling at the BH alter
I am a pretty smart guy - I spend most of my day being a trusted expert at work, and people pay me to be trusted expert in my consulting business. I come here, and I am instantly reminded how phenomenal the talent, intelligence and experience the Bottlehead Community has collectively in its ranks. It is humbling and I am incredibly thankful for how generous everyone is with their time and knowledge. I am happy to take the title of permanent Newb