What is the different between guitar and bass preamp?

[nguitar12]

Just wonder what is the different between guitar and bass preamp?
How can I modify this guitar preamp for my bass?

[anotherjim]

Well, there is of course a long history of guitar and bass amps being liked for either duty. Probably the biggest difference is the speaker cab required for dedicated use of one instrument or the other.

For the circuit shown, a high gain setting for the Level control will cause loss of bottom end (the high pass filter in U1b with the 470nF and only 4k7 with Level control at minimum resistance. I would replace the 470nF with a 1uF electro cap, but it's negative wire will then connect to ground instead of Vref.  The rest (ignoring the tone stack) will be fine even with a bass with a low B string.

There is a logical approach that bass guitar tone stacks should simply be shifted down an octave (halve the Fc), but IMO that is a matter of taste and bass style, and you might only lower the Bass control to the extra bottom end. Should be able to model this in the Duncan Tone stack calculator, but maybe a start is to raise the 47n for the bass control to 68n or 100n. Again, IMO, you would best breadboard it and listen to it with the intended amp & cab and intended volume levels. The mid shift options in the circuit might get you where you want without altering anything else.