@bernardo_furtado Welcome to the BassBuzz forum!
When you have time, join us on the Introduce Yourself thread.
This is a lot of information and it’s going to take a little while to unpack all of it since there are a number of different things going on with your gear. I’ll try to address what I can and hopefully others will chime in and fill out some of the details that I miss. I’ll take some of the easy stuff first and then get into some of the more complex issues.
I know you were kidding around but I want to be clear that the modern Squier basses are considered a really good deal in their price range. Any use of the word ‘cheap’ was probably meant more along the lines of ‘inexpensive’ rather than ‘poorly made’. Lot’s of people on BassBuzz really enjoy their Squier basses.
I tried the Audio Technica ATH-M50x with my Fender amp and didn’t have this issue but I wasn’t having the grounding problems you’re having.
The main difference between the Audio Technica headphones and your other headphones are the Audio Technica’s are designed to give a flat response where the others are designed to make listening to music better. What this ends up doing is making any sound problems more pronounced. My best guess is that is what’s going on here.
Josh generally recommends using whatever headphones give you the best listening experience. As long as they have good bass response, then that’s all you need. Given the cost of these in Brazil and the fact you already have headphones you like, might not be a bad idea to send them back. That’s a call that only you make.
Pickups work like antennas and pick up all the environmental electromagnetic interference and that creates hum and buzz. Humbucking pickups are designed to negate this.
Jazz bass pickups (and all single coil pickups) when used by themselves, as in your example, don’t have this hum canceling effect. However, when you use the pickups together, it does create a hum cancelling effect. That’s why you see those changes when adjusting the pickups.
Having said all of that, the buzz and hum still shouldn’t be what you are describing.
If I understand all this correctly, this should only happen if the bridge is not connected to the ground. Maybe @terb @howard @Korrigan or one of the many others that know this stuff better than me can chime in to confirm.
Hold off on worrying about this until you get to the end though.
Yes, definitely getting some EMI. This gets back to the ground connection to the bridge. It’s impossible to tell how much of a problem the EMI really is if your ground isn’t connected all the way through.
Since the buzz is on the high end when you increase the high end it’s going to increase the loudness of the buzz. The overdrive on the Fender is more pronounced on the high end. That’s why you would hear more with the overdrive on.
This is where it all gets even more complicated. Specifically the part where the amp still buzzes with no cable plugged in. The makes me think the amp is what’s giving you the biggest problem as opposed to a possible problem with the ground connection to the bridge.
If the amp is picking up the interference causing the buzz then touching the strings won’t matter since the buzz is being introduced in the amp and not the bass.
The first thing I would try is moving the amp to different outlets in different rooms to see where you get the least amount of interference. Also try turning off other electrical devices to see if they are having an effect on the amp. Once you figure out what’s causing interference there, then you can move on to looking at what might or might not be happening with the bass.
I hope some of that helps and let us know how troubleshooting goes. I’m curious to see what you find.