Adding frequency control to fixed 4-band EQ?

[Taylor Livingston]

I'm interested in adding some frequency control to my Univox amp. Here's the schematic:

http://www.schematicx.com/view-schematic/univox-u-1011-amplifier-schematic/

Ideally, I'd like for bass, mid, and treble to each have a frequency sweep knob (for some reason I don't see the treble control in the schematic - either my eyes are getting bad rather early, or it's missing from the schem). I don't know if that would be as simple as replacing some resistors with pots, or if it would be more complex than that. I would be ok with freq. switches if continuous control would be too complex.

Any suggestions on how to do this?

 

[BassmanPaul]

Treble control is the pot above the Bass control. To do what you ask you are going to have to go active I should think. You just don't have enough hardware. You gan try changing the cap values but there is only do much that you can do with a passive tone stack.

Paul