Solved 16khz treble spike in bass guitar pot.

[CoolName]

Hi. Anyone care to offer a theory as to what's going on here with my bass? Treble control on bass all the way off in one picture. Treble all the way on in the other pic. There's a 16khz spike when the treble is on. The more treble you add on the bass the bigger the spike gets.

Fender P-Bass about 5 years old.

Thanks

 

[mcascone]

Doesn't that make sense? The treble frequencies should be cut when it's down, and normal/boosted when it's up.

 

[gabo]

Does it make a difference when you move the bass around, turn it different directions? Could be that it's picking up some interference from something, wifi, microwaves, radio station, etc. If it is, when you turn the bass different directions it should change a bit.

Also, is there a difference when your fingers are on the strings? How about if you touch the bridge plate? The strings and plate should be grounded and it's not uncommon for it to make more noise when you're not touching it. If it doesn't change either way, then the ground wire might have broken or gotten disconnected. There is also a capacitor on the tone control.

It's probably not coming from the POT, more likely that it's coming from the pickups and the POT is just reducing it when it's down.

There is nothing complicated about a P bass wiring, so open it up and see what's going on. You should be able to verify the connections. It's Relatively easy and cheap to replace the CAP and POT. Wiring diagrams for it are easy to find via your favorite search engine.

If the pickups work, they are probably good. Pickups are really simple and robust as they are just wire wound around a magnet, if they make sound they are probably good.

good luck!

 

[lokeyfly]

Hi CoolName,
First, are you hearing the spike? Or only questioning what's visible? You never mentioned if this was audible.

There are what could be a few causes, but let's consider 16khz, few people above the age of 35 yrs old can even hear. With that, you still want to kill any residual spike-like frequencies on your bass with a LPF (low pass filter). So a good cutoff frequency where you're still getting good punch, slap, harmonics etc. would be around 4k. That's being VERY considerate to just about any attainable sound from your bass. More like 2 kHz of LPF cuttoff would be more practical.

As to why that 16 kHertz spike is occuring could be a subtle transient, perhaps a leaky capacitor, maybe fretting buzz, or some issue with the coil winding. Maybe a non potted pickup, acting like a microphone and picking up some neighboring RF around your location (causing a spike). Maybe light fader which causes a buzz on that circuit in your house which is only a 60 cycle hum, but perhaps causing some spike. Poor shielding from the guitar, chord or connection might be a contributing culprit. Spikes are never a good thing, but that's why I ask if you can hear it?

While you're using filter cutoff, don't forget to set your HPF to around 60 to 80 hz as well.

 

[SwitchBack]

Weird frequency spectrum anyway with that buildup towards 20kHz, which looks like HF noise or foldback. Something not right with the preamp/recording interface? What was the recording format (sample rate and bit depth)?

 

[Craig Anderton]

I vote for the electromagnetic interference theory. Pickups are called pickups for a reason - they pick up a lot of stuff.