I’m getting a hiss with my Directstream DAC and certain tube amps. It sounds like white noise, very steady, a bit lower pitch than whtie noise.
The strangest thing is that the noise is not there with no music playing, it starts when I play music and then it stop about 1 second after I hit pause. So the DAC must be muting itself with no digital input or something.
But I don’t know why it’s there with some tube amps and others are dead quiet with it. I’m suspicious it’s always there and certain gain stages make it more audible which also kind of haunts me that I’m alays hearing this digital white noise hash. Also interestingly, one amp that makes the hiss uses.6SN7 tubes and some brands bring it out more than others… I’m guessing slight differences in gain but again not sure.
Some troubleshooting…
It’s not there at all with the DAC plugged straight into an amp that makes the hiss.
But it is there when the DS is plugged into an RCA switcher and then to the amp. And I figured there was something wrong with the switcher so I got one on amazon and it’s the same! The first switcher was custom made for me by a talented friend, and had all separate grounds and the best parts possible - elma switchers and OCC copper hoookup wire, this new one is well who knows it’s from amazon. But the switcher doesn’t seem to be the issue itself since it’s there on both switchers.
But it has to be the DS somehow connected to an RCA switcher because it completely went away connected directly to an amp that brings out this hiss. and the Chord TT2 didn’t make this hiss with the same setup but I can’t listen to the TT2 after hearing the DS mkii. 
Any ideas? It’s driving me nuts. I can’t listen to half my setups.
thank you!
edit: sorry i forgot to mention my chain
Streamer: Pi2Design Mercury V3 (not likely to be the culprit because I’ve tried 2 separate units unless there’s an incompatitibility issue)
Tidal/Qobuz → UPNP → Jplay on iphone 13 mini → Mercury streamer → I2s → DS mkii → switcher → amps
These are all headphone amps or efficient speaker amps used for headphones, I only use headphones right now.