Having experienced some remarkable results in tuning TD-160 motor (see here) we were quite curious about the effect of tuning the capacitor for a Papst motor. We also wanted to know whether decoupling the Papst motor with the springs used for the E 50 motor, would improve the Papst.
The Papst can be a very quiet motor, provided that the phases of the motor are properly tuned. The standard 470 nF capacitor used by Thorens is a far from optimal value. Deviations from the suggested 500nF (by Papst)  induces quite an amount of electromagnetic vibrations when used in the Papst. Now this value is not sacrosanct. Each individual motor has its own individual properties and the capacitance required varies accordingly. The graphs below show the improvements when this is done properly. As you can see there is a combination of capacitors in order to obtain the 530nF that was required for this specific motor.

 

papst tuned capacitor   papst spring mod
Papst wired with correct capacitance       Papst suspended in decoupling springs

 

 

The graph below show the noise spectrum of the TD-124 with a Papst motor with a standard 470nF capacitor and mounted with standard decoupling rubbers

standard cap and rubbers

The square indicates the motor's 100 Hz electromagnetic vibration. Here it is found at -67dB, measured on the chassis with a Bruel & Kjaer accelerometer.

 

 

Below you see hat happens when the capacitor is tuned to the exact right value. Here the motor is still suspended in decoupling rubbers.

tuned capacitor and rubbers

The 100Hz vibration is now measured at -75dB

 

 

The last graph shows the Papst motor properly tuned and suspended in springs.

cap and springs

The 100Hz has dropped yet another 5 dB. This results in an overall improvement of 13 dB!   Now listen to that!