As a guitarist, very familiar with the various types of noise that can wreak havoc with electric guitars, I've been mystified at how infrequently guitar amplifier inputs have employed differential stages. Of course low impedance microphone inputs have done so for a long time, specifically to reject as much common mode noise as possible, especially given the typical use of long cables. Now I understand that most magnetic pickups used in guitars have comparatively higher outputs then microphones. But these guitar pickups generally perform best when connected to high impedance inputs, which always works against noise immunity, and their amplifiers need to cover a very wide dynamic range. Of course many guitars employ dual coil "humbucking" pickups, which help null out both electric and magnetic field induced noise. But all such approaches change the sound, and many players favor the tonal quality of simple single coil pickups.
So my question here is simply whether the failure to transition to balanced differential inputs for guitars is due to some disadvantage I'm not taking into account, or if its simply a matter of how difficult it is to change the "status quo" with anything related to audio and psycho-acoustics. I've made many home brewed amplifiers over time, and have re-wired enough guitars to consider all kinds of experimental changes. And of course a differnial input can still function with an old fashioned single conductor coax cable. But I'd still like to hear from others on this. If differential inputs have drawbacks I'm not considering, it wouldn't be the first time I thought I had a better way to do things, and was later proven dead wrong.
Best Answer
If the guitar pick-up were all that were in a guitar body then it would make sense to wire it differentially back to the differential input amplifier. That's where the story ends because to make the volume pot(s), tone pot(s) and pup-switching balanced needs much more complication.
So, what about a standard guitar feeding a balanced input? No big benefit. To be balanced you need: -
So, there is no benefit wiring an unbalanced signal and impedance (wrt ground) to a balanced input. In fact you are likely to cause common-mode problems on the input because of all the capacitamce to ground through the body when intermittently touching the strings.