Is the SUT working OK Oliver?
Is the SUT working OK Oliver?
It is impossible for anything digital to sound analogue, because it isn't analogue!
Location: KY - Scotland
Posts: 5,470
I'm Mike.
SUTs can be very quiet indeed - I'm sure the problem with yours can be sorted, you just have to be methodical about tackling it. I recommend using a pair of shorting plugs, or a pair of shorting plugs and shorting sockets if you're going to be really thorough. Here's the procedure:
1) Disconnect the SUT from the mm phonostage and put a pair of shorting plugs into the phonostage. The noise should be very low - just a bit of hiss when cranked up.
2) Put a pair of interconnects into the phonostage's input sockets and a pair of shorting sockets into the other end of the interconnects. The noise should still be very low. Try it with the two shorting sockets kept separate and also with the two shorting sockets touching each other. If it's silent with the sockets separate but hums when they touch, it's because touching them together has created an earth loop between the left/right earths. Some phonostages will hum when a loop is created this way, some won't. Whether or not it matters depends on whether or not the SUT creates the same loop. Some SUTs will, some won't.
3) Remove the shorting sockets and connect the SUT's outputs to the phonostage. Put the shorting plugs into the SUT's input sockets. There should be very little noise - no more than the phonostage alone. You should find that the orientation of the SUT and its proximity to other equipment's main transformers will affect the level of audible hum. Move the SUT around and listen to how the hum changes. The place on your equipment rack where you intend the SUT to reside may not be the best location for it. Find a place which gives the lowest hum. Sometimes just having the SUT on its side can reduce hum dramatically.
4) Connect the turntable to the SUT. If the SUT was quiet before but it now hums, the problem is with the turntable rather than the SUT. The turntable's ground wire should be connected to the phonostage's ground terminal. An extra ground wire between the phonostage's ground terminal and the SUT's ground terminal (if it has one) may or may not be required. Try it both ways to find out.
The above procedure should sort out any problems. Be aware that shielded cable between the SUT and phonostage is essential for low noise. Some esoteric cables aren't shielded and will cause problems.