Just some questions on in-lines

[kb9wyz]

hmm; maybe there was a bad ground or improper shielding going on, and that got corrected in the process of installing the preamp.

a preamp is gonna boost everything (including noise) when turned up; that's why they're usually paired with hum-cancelling pickups.

You know, you're probably right. I tried to think about how else one could eliminate noise with a preamp, but my best solution came up flat. This does seem like the most likely thing because when I installed the preamp, I also redid the ground.

I thought maybe there could have been an extremely narrow notch filter in the preamp at first, but B1 is so close to 60Hz that the filter would have to have it's -3dB at +/- 0.5Hz with a rolloff that defies physics.

So thanks all for pointing out my WILD misconception and correcting it. Much appreciated.

 

[walterw]

my understanding is that even that theoretical notch at 60Hz wouldn't do it, because the hum isn't just a pure sine wave. all the harmonics (120Hz, etc.) would have to be knocked out, too.

 

[line6man]

my understanding is that even that theoretical notch at 60Hz wouldn't do it, because the hum isn't just a pure sine wave. all the harmonics (120Hz, etc.) would have to be knocked out, too.

Most of the energy is in the 60Hz fundamental, but a lot of it is in the harmonics. FWIW, 120Hz is a common hum frequency on things which are powered by DC that was full-wave rectified from 60Hz AC, as the ripple occurs at 2* the input frequency. Basses are generally powered by batteries, which are free of ripple, so theoretically, there could be less energy at the 120Hz point, but 120Hz is still the loudest harmonic above the 60Hz fundamental.
At the end of the day, the harmonics are too loud for a simple 60Hz notch filter to knock out the hum. You need to go up to the fourth or fifth order harmonic to get rid of 60Hz hum, and even then, it's of questionable effect.