Bigguy2017

Sounds like the ground side is not grounded somewhere... Does it have a ground wire between the pots or does it use the plate for grounding ? - tighten all three pots and the jack onto the plate. Get a croc lead and short the jack ground to a vol pot ground - does that pot now go to zero? Jazz Bass WIRING 01D.pdf

Hmmm... weird one... You've tried all the obvious so it must be something else. Things to try; You could have a weak pickup magnet on the E string (you've changed the pickup so probably not this) - tap all the pole pieces with a (steel) allen key - do they all make a similar bang and are they all similarly 'sticky'? Nut. Have a good look at the nut slot for the E string - is the slot cut right and is there a tiny clearance (try a sheet of paper) over the first fret when string is fretted at fret 3? Also check the E bridge saddle. Room. Are all your listening test being done in the position in the same room? Room dimension s can really effect the low end - my living room has a big peak around A which sounds much louder than it really is. Try with another cable, direct to the amp - there can be odd effects if the cable's conductive plastic layer is not stripped back correctly. (clutching at straws here). What bass, what pickup, what strings? It is possible to wire a PBass or stacked jazz pickup out of phase which makes for a weird response.

Get some bigger Genelecs.

Standard M5 Nylon 66 washer is 5.3mm ID 9.5mm OD 1mm thick - so basically correct https://www.flexibleandfasteners.co.uk/Shop/m5-nylon-metric-plastic-washers/ https://www.amazon.co.uk/M5-Nylon-Washer-Washers-Natural/dp/B006XURJH8 These are nearer M5 x 7.5mm, also nylon... https://www.amazon.co.uk/sourcing-map-Nylon-Washers-Screw/dp/B07NRYZG81 https://www.ebay.co.uk/itm/362586035318

Anyone know what size (ID and OD) they need to be? M4? nylon and PTFE washers are available for pennies...

Rubber O rings might work ?

Possibly a bad solder joint on the neck pickup / pot ?

If Deoxit doesn't fix it then replace the pots.

That size is a Neutrik D-Series - panel has a 24mm hole (also known as Universal Format Connector). M3 countersunk - usually 10mm or 15mm long, plus a plain washer, lock washer and a nut (M3 Nyloc can be used). If doing a lot of them get an M3 nut driver/spinner...

If relief is AOK and minimal check the nut slot heights. Get the fret rocker out... any high frets will ruin a low action. If fret rocker shows high frets then a spot or full fret level is indicated.

I sound a little bit conservative.... Columbus Fender Musicman Aria Rickenbacker EB Musicman Fender Fender Fender Fender Fender

From the picture it looks like all four string slots are 1mm towards the E side - way too much wood showing on the G side. It needs a new nut.

Try Home - Marten Cables they can make to length with HO7RN-F Rubber Cable Also https://www.designacable.com/

Meant for an upright acoustic bass?

That is a classic example of 'green goo'. It happens when the plasticiser in the insulation reacts with the copper wire and corrodes it. It's a manufacturing defect in the cable and was (is?) reasonably common in mains (and other) cables of a certain age of manufacture. Google 'green goo in cables' What To Do About Green Goo | No Shock Electrical Only fix is to bin the cable and replace.

No, it isn't. I've fixed so many dirty pots with Deoxit and it is actually formulated for this purpose. Also if the pot's f!*ked anyway what have you got to lose? It's easier than replacing the pot, which may finally be necessary. Over 45 years as a Broadcast Engineer I have never had Deoxit harm a pot - cleaned literally thousands of carbon track pots this way - entire mixing desks. Don't believe ignorant chat on the internet... https://caig.com/cleaning-and-maintaining-pro-audio-gear-deoxit/

Does tapping the knob produce the crackle? Could be the pot itself or it could be a dry solder joint. Give the pot a squirt of Deoxit and a few twists. Resolder the pot's connections on the PCB. Tap around the PCB with a plastic pen or similar, to identify dry solder joints - reflow any suspects... Replace the pot.

lighting stand top plate / tilting top plate ? In lighting circles I've seen similar called a baby plate ... I'm not finding anything small exactly like this - closest are adjustable AV/speaker stands Pyle Pro Swivel/Adjustable Wall/Ceiling Speaker Mounts PSTNDC31 Acesonic NB-901 Speaker Mount Headliner HL31001 Speaker Stand Mounting Plate for TV, Monitor, Projector, or Moving Head A much chunkier thing is a Unicol CP6 tilting ceiling plate, so a small projector ceiling mount might do...

The Polytune also has a DC loopthrough so one PSU plus a single short DC cable will power these neatly.

They never seem to last for long. Switchcraft are better than most. Has anyone tried the Pure Tone ones with four spring contacts?

Yes, looks like there is an open circuit in the pickup - as the two halves are in series it could be in either one. Unsolder / clip the black + white pickup wires and check for continuity - you should see around 8.5K to 10K Ohms. If open circuit unscrew the pickups and have a good visual - check the fine coil wires where they are soldered to the output wires. Check each half for contunuity - expect around 4K to 5K per coil. Carefully reflowing the solder joints on the pickup wires may fix things...