I have an interesting issue. I have three amps - Stax SRM-353x, Jotunheim R, and the THX 789 - for different types of headphones. I would like to have all three plugged in to my DAC at all times, so I don't have to switch the cables around when listening to different headphones.
So I bought four XLR splitter cables and wired everything up. Since the amp inputs are high-impedance, I figured this would work, and it mostly does. Except, when I'm listening to either the Stax or the Jotunheim and the THX is off, the sound coming from the Stax or Jotunheim is severely distorted. I have to unplug the splitter cable from the THX to make it listenable.
However, I discovered that if I turn the THX on, even if I'm not actually listening to it, the signal recovers and sounds normal again. With the THX on, the other amps sound the same whether or not the THX is connected. Only if the THX is connected and off does it drag down the signal.
Weirdly, only the THX seems to do this. I can listen to the THX while the Stax and Jotunheim are connected and off, and it sounds fine. Likewise, neither the Stax nor the Jotunheim seem to mind the other being connected. But if I listen to one of those two while the THX is connected and off, it sounds horrible.
Anyone know what's different about the THX circuit that makes it do this? I'm thinking maybe an ESD protection diode on the input.
I guess I'll have to get one of those XLR switch boxes, unless someone knows of a better way to fix this.