Lee_M
Well-known member
Hey guys,
I just picked up an old BBC attenuator module and there was a strange LC filter board fitted inside the module, but not actually electronically connected to anything. The board is labelled with the same BBC code number as the module it was fitted into (AT2/7A), so it seems fair to assume that it's an original part and was designed to be connected to the 600Ω balanced attenuators that make up the rest of the module, but I haven't managed to find any information about it online.
I've drawn up a schematic (see attached image), L2 and L5 are currently unidentified values (the other inductors have hand-written labels on them) so I'd need to desolder them to take measurements. They look identical to the other inductors, so I'd expect them to be in the same ballpark as 1.14mH.
Can anyone tell me what exactly it's doing? It seems to be some sort of balanced notch filter, but C7 and C8 look like they're doing something else.
Cheers!
I just picked up an old BBC attenuator module and there was a strange LC filter board fitted inside the module, but not actually electronically connected to anything. The board is labelled with the same BBC code number as the module it was fitted into (AT2/7A), so it seems fair to assume that it's an original part and was designed to be connected to the 600Ω balanced attenuators that make up the rest of the module, but I haven't managed to find any information about it online.
I've drawn up a schematic (see attached image), L2 and L5 are currently unidentified values (the other inductors have hand-written labels on them) so I'd need to desolder them to take measurements. They look identical to the other inductors, so I'd expect them to be in the same ballpark as 1.14mH.
Can anyone tell me what exactly it's doing? It seems to be some sort of balanced notch filter, but C7 and C8 look like they're doing something else.
Cheers!