Randall Preamp problem

[Organtis]

So I have this Randall th75  and a trusted friend told me the only issue is the input Jack broke. Well I wired a Ned one up and I get connectivity but there is a huge loss of low frequencies as well a loss of volume overall and it is very staticy.

I'm leaning to a bad op amp or bad capacitor. There are no tubes either. What do you think I should be looking for?

Here is a video
https://youtu.be/woOkw_q9t24

[GibsonGM]

You'll have to take it step by step...can you get hold of a schematic?   I agree, this is much more than an input jack - but also, much less than something horrible, lol. 

I think you're on the right track - I would get the schema, and think about audio probing.  It could be as simple as a bad pot, or more, like a bad cap or network.