An Op Amp can be wired as a buffer to the preamp and will have a very high input impedance if done correctly.
We shouldn't overstate this, however. 50k to 100k is good.
HIGH Impedance, such as most electric guitar and bass pickups and instruments, some (usually lower priced) Microphones (some can be low impedance, check the specs), most effects boxes, most preamps and instrument "processors" (stomp boxes), some of which may have both low and high impedance output jacks. "High" is probably the most common input impedance value in our musical input world, and the generic term "high impedance" is used quite often.
High Impedance devices are most often (but not only) found plugged into high impedance ¼ inch phone jack inputs in instrument amplifiers, PA boards, effects boxes, preamplifiers, etc. Input impedance values vary, but some typical values are 44K, 220K, 60K (usually active) and 800K, 100K (typically passive). It's ok to plug high impedance instruments and devices into ultrahigh impedance (1MegOhm and higher) inputs.