Q. Are the MA28 and MA31 interchangeable, and can I use a turntable with the MA28?
Answer:
The MA28 was for adding a CD player to a Tuner input whilst also retaining the Tuner. It attenuates the CD output, so it won't overload the tuner input which is typically 300 mV sensitivity. If you also use this to connect a record player to a line level input on an amp, you won't hear anything. Conversely, if you use this to connect a record player and a CD player to the phono input on an amp the record player will be OK, but the CD player will be very distorted, and have too much bass and no treble, just before the phono stage goes pop because it has been overloaded.
The MA31 was for adding a CD player to the phono input of a boom box, or music centre which only had turntable input sockets while also retaining the turntable. It attenuates and EQs the CD player, so it looks like a moving magnet turntable output to the amp. If you use this on a normal line level input, you won’t hear anything.