...A Y Splitter (presumably) is simply copper wire joining all of the connectors in it. Hence, if you use a Y splitter between the L and R on the amiga to gain a mono audio signal for your modulator, anything else connected to your amiga stereo audio output will see both the L and R signal as being identical as they are now shorted together via the Y connector - Ie, they now also appear as mono.
I suggest you make a small splitter box that takes the audio from the amiga output and passes it through unaltered to two sockets on the case (This feeds your monitor), and that also contains a resistor from both of the L and R signals, joined at the centre, where the centre of the two resistors then goes to a third socket on the case and feeds the modulator as a mono audio signal.
The resistors could be anything from 1k to 10k, just try different values and see what works best with your monitor -Just make sure that they are both the same value as each other. Oh, and dont forget to connect all of the grounds/connector outers together.
This way you should have a mono output for your modulator and a stereo output for your monitor.
Hodgkinson.
