Nac 52 boards

The forum FAQ tells all....

https://forums.naimaudio.com/to...phono-boards---which

Guenter - This is from the original manual around 1992 - not sure if other boards were introduced subsequently.

INPUT AND OUTPUT SPECIFICATIONS

Input 1 options:
NA 522 for moving magnet cartridges                                   . . 2mV/47K Ohms
NA 523S for low output moving coil cartridges                    .. 100µV/470 Ohms   
NA 523K for Karma/Troika type cartridges                           ..100µV/560 Ohms
NA 523E for medium output moving coil cartridges           . .350µV/560 Ohms
NA 526 for line input (fixed)                                                     . . 75mV/100K Ohms
NA 528 for line input (variable sensitivity)                            ... 25 - 350mV/47K Ohms

lnput 2, 3, 4, 5 & 6 (standard - as supplied)                        ..75mV/100K Ohms

Input 5 & 6 options:
NA 528 (variable)                                                                     ... 25 - 350mV/47K Ohms
NA 526 (fixed)                                                                         ... 75mV/100K Ohms

Output 4, 5 & 6 (standard - as supplied)                           ..... 75mV/600 Ohms

Output 5 & 6 options:
NA 528 (variable)                                                                    ... 25 - 350mV/600 Ohms
NA 526 (fixed)                                                                         .. . 75mV/100K Ohms

lnput sensitivities are referenced to 0.775 volts output with the volume at maximum. The inputs will accept input levels 100 times the rated sensitivity before clipping (40db overload margin)

Paqe 14

Hope that helps 
Sam

PS.  I see Richard beat me to it...

Guenter, you should contact Naim customer services by e-mail who should be able to supply a copy of the NAC52 manual in pdf format.