Jazz Wiring Advice?

[Matthew_84]

So, I have all weekend (will take my time) to do various jobs on my fretless jazz. One of the tasks is to shield the cavities and change the pots and jack. The cavities have been painted with shielding paint, and there are wires that run from each pickup cavity back to the control cavitiy that are grounded, but the bass still hums a lot, especially with my hands off of the strings, bridge, or control plate. I know there will always be a 60hz hum with the pups at different volumes, but this seems a little excessive. I am hoping to improve it slightly. I have never done any wire soldering (have done plumbing), but I do have a basic understanding of electricity and am decent with troubleshooting low voltage circuits.

Here's what my current cavity looks like:

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The chrome cover plate is basically acting as the conduit transfering the pickups, pots, cavities, and bridge grounds to the ground on the jack. I'm still a little surprised how much hum is present though, and how much dissipates when I touch the strings. It's probably not really all that bad. My house's wiring is horrendous, which exaperates it, but I would like it to be quiter, if possible.

I plan on putting copper shielding tape in all of the cavities, and in the wire routes between cavities, soldering the joints together, and ensuring there is 0 ohms between every point, then wiring the bass up as follows:

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Would this make any improvement at all, or not? Could it potentially make matters worse?

Thanks,

Matt

 

[Matthew_84]

Sorry, but I need to bump this. I shielded the cavities with copper tape, and there was about 0 Ohms anywhere I checked. I couldn't run the copper tape through the wire routes, so I just re-ran the wires that were in the cavities in the existing drawing and terminated them in the central ground location. I then wired as shown in my proposed drawing, except that I removed the conduit running from the jack ground, as I realized it was redundant.

I have read that it's best to have one path to ground, and that's what I set out to achieve here. There is no difference when I touch the strings or not, which is amazing, but the 60 cycle hum seems to be louder now, which I didn't realize could happen. Is there anything I should do differently?

 

[Skatman]

Your ground needs to follow the the signal path, Im drunk and this isn't the cleanest but check your grounds and make sure you're using the right wires, 2 conductor in the right places

 

[Matthew_84]

Thanks Skatman. I've checked everything, and even added more solder to the joint where all the grounds meet before they're screwed to the copper in the control cavity. All of the solder joints look good, and when the plate is screwed on, I get 0 ohms from the plate to the bridge.

I don't really get what could be wrong. The resistance in the shielding has been greatly reduced. I did remove the stock Squier pots and "2A503J" tone cap, and put in CTS pots and a .047 cap. Not sure, if that would cuase this though. The tone is much better though, clearer, and maybe a bit higher... I guess causing more highs/hum to come through. But there's quite a lot more hum then before. I don't know.

 

[96tbird]

Single coils are going to hum; thats life. My basses hum and are quiet when I touch them. Grounded is grounded, period. Don't listen to goofy ground fables for a passive setup. Shield the cavities and maybe shielded wire can help beyond that, only humbuckers help.

 

[Im a sock]

Check out the Jazz Shielding sticky at the top of this forum (go to the last page of it for a PDF with the pictures on it). I followed this procedure last weekend and my bass is dead silent - it's an SX Jazz with SD Quarter Pounders - as long as both pups are dimed, it's completely quiet.

 

[Matthew_84]

Yeah, I have read through it, not all of it, but half a dozen pages or so, including the .pdf. I think I did a good job, it is completely silent with both pickups fully open, even with my hands off the bass. I do know that single coils will hum when they're not even, it just seems to be louder now, but I'm not sure if there's anything in how I re-wired it that caused it, or if it's just the new pots and tone cap that do sound quite different that's causing it.

 

[frits51]

Dont' know if anybody will see this so long after the original post.

I have an MIJ Jazz that I modified with an S1 switch (push-pull switch on the volume pot for series/parallel switching). Also added a Bourns blend pot. Vol-Blend-Tone.

Bass is very quiet, even when soloing one of the single coil (originals) pickups. Tiny bit of noise, but not a problem at all.

About the grounding - I grounded each component with its own dedicated wire, then soldered the ends of those wires together. How many ground wires?

Pickup, pickup, volume pot case, blend pot case, tone pot case, tone capacitor and bridge = seven wires, all brought together and soldered. The 'star' configuration.

Some on these forums have said it's impossible to have a ground loop in a bass, so 'star' grounding is not needed. That's not my major point. I would rather have a common copper ground path for each component rather than relying on a steel pot case to provide a low-resistance path. In guitars, we're talking very low voltages. Any resistance that voltage encounters will possibly have an effect. Looking at your pic, I see the tone cap grounded only to the tone pot case. Can't tell, but there may be other such groundings.

 

[MetroBass]

I just swapped out pickups in my Squier CV Jazz with Fender CS 60s and replaced the Alpha pots with CTS pots and I don't have any hum. I also carried the ground from the input jack to all the pots like their diagram says. No shielding or grounding other than that which comes with a Squier (which is nada). (I didn't bother using the supplied pickup shields that were included in the kit either)

You may have another source or may have induced it yourself with the misc. grounding and shielding. It may sound stupid but I'd go back to basics and remove all the shielding and assemble the electronics in the simplest fashion possible. Sometimes our over thinking things gets us into a quandary we can't get out of. Also, you may want to make sure the ground from the bridge back to the electronics is sound.

The Squier has to be far less superior than a MIA and from purchase to my current mods no hum. FWIW: I used the Fender diagram for the '75 American Vintage Jazz Bass.

 

[walterw]

I think I did a good job, it is completely silent with both pickups fully open, even with my hands off the bass.

then you won!

that's what shielding does for you, reduces the extra buzz when you let go of the strings.

it won't help with regular single coil hum at all.

maybe you're now just hearing a bigger difference between the quietest state and the same noisy state.

(the bridge is still grounded, right?)