Stereo input transformer EMT pickups
TSD 15 ... XSD 15 --> STX 21 --> preamplifier (phono)
Pay attention to the correct earth connection at STX 21.
To avoid earth loops the earth connections should be led to a central point, which means the principle of a starlike earth connection.
The preamplifier is the central point. From this point the earth cable shall go to the mass connection of the STX 21 and the tonearm.
If the turntable has an additional mass connection, it also has to be connected with the earth of the preamplifier. You should connect the turntable and the preamplifier only if there is no connection between tonearm and turntable.
Like every transformer the STX 21 is sensitive against magnetic fields. To avoid hum in the audio signal, keep STX 21 away from producers of magnetic fields like power transformers, power cables, television sets, power amplifiers etc.