Is there such a thing as a stand alone tone control?

[Sonny]

I'm not talking about a GE, I don't like those. I mean a box with treble and bass control that goes between source and amp?

 

[spiny norman]

I'm not talking about a GE, I don't like those. I mean a box with treble and bass control that goes between source and amp?

Well, there was this, but you may have to hunt around a bit to find a secondhand one.