San diego Sound..Preamp?

[ultima]

I just aquired a mic preamp that i know nothing about and im hoping someone here has heard about it.

The only labelling i can find is this sticker on the back saying San Diego Sound Inc.

This thing seems pretty old This thing is old as far as i can tell.

I dont have a picture.....

The mic input on the back is five pins?

Six RCA connectors on the back and one of them is an input as far as i can tell...(no labelling)
two of them seem to be outputs with Hi and Lo output?

This thing has a very nice filter section ( only thing i have manged to try out) where you can set it to AP/LP/BP/Hp and has filter cutof and Q...this filter can scream!!

Then there´s Gain and next to that is Max.Output

Then we have a Vu meter thats switchable between I/O.

What im very interestd in knowing about is the next section...

Two knobs marked Horizontal gain and Vertical gain??

What is that ...something to do with sum&difference ?

Anyone heard of this thing?

Thanks