I can't seem to find any detailed information regarding the empegs RCA outputs. I remember someone saying it had a 4V output signal but I need details like the ohm and kili-ohms.

I was speaking with a service person at an alpine dealer and explained my 'cassette hiss' between the empeg & alpine and he wanted to know what these values were. He said it's possible that these two devices don't "like" each other.

More likely that you have the output gain of the empeg too low to the line in on the Alpine, and you are hearing the noise in the Alpine's amp if you have to turn it up to high volume to hear the empeg properly.

He should not need to know about line impedance if he is using a line out-line in connection between the two units.