Almost everything was rated at 500mv back then

It's amazing we could actually get stuff to work

 

I received a message from someone on another forum who said this:

"The HU actually puts out 3V with impedence output of 4 Ohms only. Lowest
impedence HU ever built. One of the last head units with a discrete power supply. No tuner. An external tuner was optional. The optical is a bit sensitive to vibration. So, securely mounting the HU is
critical. MSRP in 1991 $900.00"

Interesting.